diff --git a/bruno/neon-sprawl-server/npc-behavior-catalog/Health after npc behavior catalog load.bru b/bruno/neon-sprawl-server/npc-behavior-catalog/Health after npc behavior catalog load.bru
new file mode 100644
index 0000000..17bd525
--- /dev/null
+++ b/bruno/neon-sprawl-server/npc-behavior-catalog/Health after npc behavior catalog load.bru	
@@ -0,0 +1,25 @@
+meta {
+  name: GET health (npc behavior catalog boot NEO-88)
+  type: http
+  seq: 1
+}
+
+get {
+  url: {{baseUrl}}/health
+  body: none
+  auth: none
+}
+
+docs {
+  NEO-88 loads content/npc-behaviors/*_npc_behaviors.json at startup (fail-fast). No NPC behavior HTTP API in this story — use this request to confirm the host started after catalog validation.
+}
+
+tests {
+  test("status 200", function () {
+    expect(res.getStatus()).to.equal(200);
+  });
+
+  test("service identity", function () {
+    expect(res.getBody().service).to.equal("NeonSprawl.Server");
+  });
+}
diff --git a/bruno/neon-sprawl-server/npc-behavior-catalog/folder.bru b/bruno/neon-sprawl-server/npc-behavior-catalog/folder.bru
new file mode 100644
index 0000000..74951ca
--- /dev/null
+++ b/bruno/neon-sprawl-server/npc-behavior-catalog/folder.bru
@@ -0,0 +1,3 @@
+meta {
+  name: npc-behavior-catalog
+}
diff --git a/server/NeonSprawl.Server.Tests/Game/Interaction/SalvageActivityDeniedRegistryWebApplicationFactory.cs b/server/NeonSprawl.Server.Tests/Game/Interaction/SalvageActivityDeniedRegistryWebApplicationFactory.cs
index c1f96b7..7a1ae90 100644
--- a/server/NeonSprawl.Server.Tests/Game/Interaction/SalvageActivityDeniedRegistryWebApplicationFactory.cs
+++ b/server/NeonSprawl.Server.Tests/Game/Interaction/SalvageActivityDeniedRegistryWebApplicationFactory.cs
@@ -11,6 +11,7 @@ using NeonSprawl.Server.Game.Crafting;
 using NeonSprawl.Server.Game.Gathering;
 using NeonSprawl.Server.Game.Items;
 using NeonSprawl.Server.Game.Mastery;
+using NeonSprawl.Server.Game.Npc;
 using NeonSprawl.Server.Game.PositionState;
 using NeonSprawl.Server.Game.Skills;
 using Npgsql;
@@ -45,12 +46,16 @@ public sealed class SalvageActivityDeniedRegistryWebApplicationFactory : WebAppl
         var abilitiesDir = AbilityCatalogPathResolution.TryDiscoverAbilitiesDirectory(AppContext.BaseDirectory)
             ?? throw new InvalidOperationException(
                 "Could not discover repo content/abilities from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
+        var npcBehaviorsDir = NpcBehaviorCatalogPathResolution.TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory)
+            ?? throw new InvalidOperationException(
+                "Could not discover repo content/npc-behaviors from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
         builder.UseSetting("Content:SkillsDirectory", skillsDir);
         builder.UseSetting("Content:MasteryDirectory", masteryDir);
         builder.UseSetting("Content:ItemsDirectory", itemsDir);
         builder.UseSetting("Content:ResourceNodesDirectory", resourceNodesDir);
         builder.UseSetting("Content:RecipesDirectory", recipesDir);
         builder.UseSetting("Content:AbilitiesDirectory", abilitiesDir);
+        builder.UseSetting("Content:NpcBehaviorsDirectory", npcBehaviorsDir);
         builder.UseSetting("Game:EnableMasteryFixtureApi", "true");
 
         builder.ConfigureTestServices(services =>
diff --git a/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorCatalogTestPaths.cs b/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorCatalogTestPaths.cs
new file mode 100644
index 0000000..0b41c6b
--- /dev/null
+++ b/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorCatalogTestPaths.cs
@@ -0,0 +1,17 @@
+using NeonSprawl.Server.Game.Npc;
+
+namespace NeonSprawl.Server.Tests.Game.Npc;
+
+internal static class NpcBehaviorCatalogTestPaths
+{
+    internal static string DiscoverRepoNpcBehaviorsDirectory() =>
+        NpcBehaviorCatalogPathResolution.TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory)
+        ?? throw new InvalidOperationException(
+            "Could not discover repo content/npc-behaviors from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
+
+    internal static string DiscoverRepoNpcBehaviorDefSchemaPath() =>
+        NpcBehaviorCatalogPathResolution.ResolveNpcBehaviorDefSchemaPath(
+            DiscoverRepoNpcBehaviorsDirectory(),
+            configuredSchemaPath: null,
+            contentRootPath: string.Empty);
+}
diff --git a/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorDefinitionCatalogLoaderTests.cs b/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorDefinitionCatalogLoaderTests.cs
new file mode 100644
index 0000000..b595075
--- /dev/null
+++ b/server/NeonSprawl.Server.Tests/Game/Npc/NpcBehaviorDefinitionCatalogLoaderTests.cs
@@ -0,0 +1,379 @@
+using System.Net;
+using System.Text;
+using System.Text.Json.Nodes;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using NeonSprawl.Server.Game.Npc;
+using NeonSprawl.Server.Tests;
+using Xunit;
+
+namespace NeonSprawl.Server.Tests.Game.Npc;
+
+public class NpcBehaviorDefinitionCatalogLoaderTests
+{
+    private const string ValidPrototypeCatalogJson =
+        """
+        {
+          "schemaVersion": 1,
+          "npcBehaviors": [
+            {
+              "id": "prototype_melee_pressure",
+              "displayName": "Melee Pressure",
+              "archetypeKind": "melee_pressure",
+              "maxHp": 100,
+              "aggroRadius": 8.0,
+              "leashRadius": 16.0,
+              "telegraphWindupSeconds": 1.5,
+              "attackDamage": 15,
+              "attackCooldownSeconds": 3.0
+            },
+            {
+              "id": "prototype_ranged_control",
+              "displayName": "Ranged Control",
+              "archetypeKind": "ranged_control",
+              "maxHp": 80,
+              "aggroRadius": 10.0,
+              "leashRadius": 20.0,
+              "telegraphWindupSeconds": 2.0,
+              "attackDamage": 12,
+              "attackCooldownSeconds": 4.0
+            },
+            {
+              "id": "prototype_elite_mini_boss",
+              "displayName": "Elite Mini-Boss",
+              "archetypeKind": "elite_mini_boss",
+              "maxHp": 200,
+              "aggroRadius": 8.0,
+              "leashRadius": 18.0,
+              "telegraphWindupSeconds": 2.5,
+              "attackDamage": 25,
+              "attackCooldownSeconds": 5.0
+            }
+          ]
+        }
+        """;
+
+    private static (string Root, string NpcBehaviorsDir, string SchemaPath) CreateTempContentLayout()
+    {
+        var root = Directory.CreateTempSubdirectory("neon-sprawl-npcbehaviorcat-");
+        var npcBehaviorsDir = Path.Combine(root.FullName, "content", "npc-behaviors");
+        var schemaDir = Path.Combine(root.FullName, "content", "schemas");
+        Directory.CreateDirectory(npcBehaviorsDir);
+        Directory.CreateDirectory(schemaDir);
+        var schemaPath = Path.Combine(schemaDir, "npc-behavior-def.schema.json");
+        File.Copy(NpcBehaviorCatalogTestPaths.DiscoverRepoNpcBehaviorDefSchemaPath(), schemaPath, overwrite: true);
+        return (root.FullName, npcBehaviorsDir, schemaPath);
+    }
+
+    private static void WriteCatalog(string npcBehaviorsDir, string catalogJson) =>
+        File.WriteAllText(Path.Combine(npcBehaviorsDir, "prototype_npc_behaviors.json"), catalogJson, Encoding.UTF8);
+
+    private static JsonObject GetBehaviorRow(JsonObject catalogRoot, string behaviorId)
+    {
+        var npcBehaviors = catalogRoot["npcBehaviors"] as JsonArray
+                           ?? throw new InvalidOperationException("expected npcBehaviors array");
+        foreach (var node in npcBehaviors)
+        {
+            if (node is JsonObject row && row["id"]?.GetValue<string>() == behaviorId)
+                return row;
+        }
+
+        throw new InvalidOperationException($"npc behavior id not found: {behaviorId}");
+    }
+
+    private static NpcBehaviorDefinitionCatalog LoadCatalog(string npcBehaviorsDir, string schemaPath) =>
+        NpcBehaviorDefinitionCatalogLoader.Load(npcBehaviorsDir, schemaPath, NullLogger.Instance);
+
+    [Fact]
+    public void Load_ShouldSucceed_WhenCatalogMatchesPrototypeContract()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        WriteCatalog(npcBehaviorsDir, ValidPrototypeCatalogJson);
+        // Act
+        var catalog = LoadCatalog(npcBehaviorsDir, schemaPath);
+        // Assert
+        Assert.Equal(3, catalog.DistinctBehaviorCount);
+        Assert.Equal(1, catalog.CatalogJsonFileCount);
+        Assert.True(catalog.TryGetBehavior("prototype_melee_pressure", out var melee));
+        Assert.NotNull(melee);
+        Assert.Equal("melee_pressure", melee!.ArchetypeKind);
+        Assert.Equal(100, melee.MaxHp);
+        Assert.Equal(8.0, melee.AggroRadius);
+        Assert.Equal(16.0, melee.LeashRadius);
+        Assert.Equal(15, melee.AttackDamage);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenNpcBehaviorsIsNotArray()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        File.WriteAllText(
+            Path.Combine(npcBehaviorsDir, "bad_npc_behaviors.json"),
+            """{"schemaVersion": 1, "npcBehaviors": "nope"}""",
+            Encoding.UTF8);
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("bad_npc_behaviors.json", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains("expected top-level 'npcBehaviors' array", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenSchemaVersionIsNotOne()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        File.WriteAllText(
+            Path.Combine(npcBehaviorsDir, "bad_npc_behaviors.json"),
+            """{"schemaVersion": 2, "npcBehaviors": []}""",
+            Encoding.UTF8);
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("expected schemaVersion 1", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenDuplicateBehaviorIdAcrossFiles()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        WriteCatalog(npcBehaviorsDir, ValidPrototypeCatalogJson);
+        File.WriteAllText(
+            Path.Combine(npcBehaviorsDir, "extra_npc_behaviors.json"),
+            """
+            {
+              "schemaVersion": 1,
+              "npcBehaviors": [
+                {
+                  "id": "prototype_melee_pressure",
+                  "displayName": "Duplicate Melee",
+                  "archetypeKind": "melee_pressure",
+                  "maxHp": 1,
+                  "aggroRadius": 1.0,
+                  "leashRadius": 2.0,
+                  "telegraphWindupSeconds": 1.0,
+                  "attackDamage": 1,
+                  "attackCooldownSeconds": 1.0
+                }
+              ]
+            }
+            """,
+            Encoding.UTF8);
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("duplicate npc behavior id 'prototype_melee_pressure'", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenE5M2GateFailsWithMissingId()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        var root = JsonNode.Parse(ValidPrototypeCatalogJson) as JsonObject
+                   ?? throw new InvalidOperationException("expected object root");
+        var npcBehaviors = root["npcBehaviors"] as JsonArray
+                           ?? throw new InvalidOperationException("expected npcBehaviors array");
+        npcBehaviors.RemoveAt(npcBehaviors.Count - 1);
+        WriteCatalog(npcBehaviorsDir, root.ToJsonString());
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("prototype E5M2 expects exactly npc behavior ids", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenE5M2GateFailsWithExtraId()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        var root = JsonNode.Parse(ValidPrototypeCatalogJson) as JsonObject
+                   ?? throw new InvalidOperationException("expected object root");
+        GetBehaviorRow(root, "prototype_elite_mini_boss")["id"] = "prototype_extra";
+        WriteCatalog(npcBehaviorsDir, root.ToJsonString());
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("prototype E5M2 expects exactly npc behavior ids", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains("prototype_extra", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenLeashRadiusIsNotGreaterThanAggroRadius()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        var root = JsonNode.Parse(ValidPrototypeCatalogJson) as JsonObject
+                   ?? throw new InvalidOperationException("expected object root");
+        GetBehaviorRow(root, "prototype_melee_pressure")["leashRadius"] = 8.0;
+        WriteCatalog(npcBehaviorsDir, root.ToJsonString());
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("leashRadius 8 must be > aggroRadius 8", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenAggroRadiusIsZero()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        var root = JsonNode.Parse(ValidPrototypeCatalogJson) as JsonObject
+                   ?? throw new InvalidOperationException("expected object root");
+        GetBehaviorRow(root, "prototype_melee_pressure")["aggroRadius"] = 0;
+        WriteCatalog(npcBehaviorsDir, root.ToJsonString());
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("NPC behavior catalog validation failed", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains("aggroRadius", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenMaxHpIsZero()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        var root = JsonNode.Parse(ValidPrototypeCatalogJson) as JsonObject
+                   ?? throw new InvalidOperationException("expected object root");
+        GetBehaviorRow(root, "prototype_melee_pressure")["maxHp"] = 0;
+        WriteCatalog(npcBehaviorsDir, root.ToJsonString());
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("NPC behavior catalog validation failed", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains("maxHp", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenDisplayNameIsEmpty()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        var root = JsonNode.Parse(ValidPrototypeCatalogJson) as JsonObject
+                   ?? throw new InvalidOperationException("expected object root");
+        GetBehaviorRow(root, "prototype_melee_pressure")["displayName"] = "";
+        WriteCatalog(npcBehaviorsDir, root.ToJsonString());
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("NPC behavior catalog validation failed", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains("displayName", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenNoNpcBehaviorCatalogFiles()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("no *_npc_behaviors.json files", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenJsonIsInvalid()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, schemaPath) = CreateTempContentLayout();
+        File.WriteAllText(
+            Path.Combine(npcBehaviorsDir, "bad_npc_behaviors.json"),
+            "{not json",
+            Encoding.UTF8);
+        // Act
+        var ex = Record.Exception(() => LoadCatalog(npcBehaviorsDir, schemaPath));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("bad_npc_behaviors.json", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains("invalid JSON", ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenNpcBehaviorsDirectoryMissing()
+    {
+        // Arrange
+        var missingDir = Path.Combine(Path.GetTempPath(), "neon-sprawl-no-npc-behaviors-" + Guid.NewGuid().ToString("n"));
+        var schemaPath = NpcBehaviorCatalogTestPaths.DiscoverRepoNpcBehaviorDefSchemaPath();
+        // Act
+        var ex = Record.Exception(() =>
+            NpcBehaviorDefinitionCatalogLoader.Load(missingDir, schemaPath, NullLogger.Instance));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("missing directory", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains(missingDir, ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Load_ShouldThrow_WhenSchemaFileMissing()
+    {
+        // Arrange
+        var (_, npcBehaviorsDir, _) = CreateTempContentLayout();
+        var missingSchema = Path.Combine(npcBehaviorsDir, "missing-npc-behavior-def.schema.json");
+        // Act
+        var ex = Record.Exception(() =>
+            NpcBehaviorDefinitionCatalogLoader.Load(npcBehaviorsDir, missingSchema, NullLogger.Instance));
+        // Assert
+        var ioe = Assert.IsType<InvalidOperationException>(ex);
+        Assert.Contains("missing schema file", ioe.Message, StringComparison.Ordinal);
+        Assert.Contains(missingSchema, ioe.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public async Task Host_ShouldResolveCatalogFromDi_WhenStartupSucceeds()
+    {
+        // Arrange
+        await using var factory = new InMemoryWebApplicationFactory();
+        using var client = factory.CreateClient();
+        // Act
+        var response = await client.GetAsync("/health");
+        // Assert
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        var catalog = factory.Services.GetRequiredService<NpcBehaviorDefinitionCatalog>();
+        Assert.Equal(3, catalog.DistinctBehaviorCount);
+        Assert.True(catalog.TryGetBehavior("prototype_elite_mini_boss", out var elite));
+        Assert.Equal(200, elite!.MaxHp);
+        Assert.Equal(25, elite.AttackDamage);
+        Assert.Equal(5.0, elite.AttackCooldownSeconds);
+    }
+
+    [Fact]
+    public void Host_ShouldFailStartup_WhenCatalogDirectoryInvalid()
+    {
+        // Arrange
+        var badDir = Path.Combine(Path.GetTempPath(), "neon-sprawl-empty-npc-behaviors-" + Guid.NewGuid().ToString("n"));
+        Directory.CreateDirectory(badDir);
+        try
+        {
+            // Act
+            var ex = Record.Exception(() =>
+            {
+                using var factory = new WebApplicationFactory<Program>().WithWebHostBuilder(b =>
+                    b.UseSetting("Content:NpcBehaviorsDirectory", badDir));
+                factory.CreateClient();
+            });
+            // Assert
+            Assert.NotNull(ex);
+            Assert.Contains("NPC behavior catalog validation failed", ex.ToString(), StringComparison.Ordinal);
+        }
+        finally
+        {
+            if (Directory.Exists(badDir))
+                Directory.Delete(badDir);
+        }
+    }
+}
diff --git a/server/NeonSprawl.Server.Tests/Game/PositionState/PostgresWebApplicationFactory.cs b/server/NeonSprawl.Server.Tests/Game/PositionState/PostgresWebApplicationFactory.cs
index dd6072b..f52eeb0 100644
--- a/server/NeonSprawl.Server.Tests/Game/PositionState/PostgresWebApplicationFactory.cs
+++ b/server/NeonSprawl.Server.Tests/Game/PositionState/PostgresWebApplicationFactory.cs
@@ -6,6 +6,7 @@ using NeonSprawl.Server.Game.Crafting;
 using NeonSprawl.Server.Game.Gathering;
 using NeonSprawl.Server.Game.Items;
 using NeonSprawl.Server.Game.Mastery;
+using NeonSprawl.Server.Game.Npc;
 using NeonSprawl.Server.Game.Skills;
 
 namespace NeonSprawl.Server.Tests.Game.PositionState;
@@ -43,12 +44,16 @@ public sealed class PostgresWebApplicationFactory : WebApplicationFactory<Progra
         var abilitiesDir = AbilityCatalogPathResolution.TryDiscoverAbilitiesDirectory(AppContext.BaseDirectory)
             ?? throw new InvalidOperationException(
                 "Could not discover repo content/abilities from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
+        var npcBehaviorsDir = NpcBehaviorCatalogPathResolution.TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory)
+            ?? throw new InvalidOperationException(
+                "Could not discover repo content/npc-behaviors from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
         builder.UseSetting("Content:SkillsDirectory", skillsDir);
         builder.UseSetting("Content:MasteryDirectory", masteryDir);
         builder.UseSetting("Content:ItemsDirectory", itemsDir);
         builder.UseSetting("Content:ResourceNodesDirectory", resourceNodesDir);
         builder.UseSetting("Content:RecipesDirectory", recipesDir);
         builder.UseSetting("Content:AbilitiesDirectory", abilitiesDir);
+        builder.UseSetting("Content:NpcBehaviorsDirectory", npcBehaviorsDir);
 
         builder.ConfigureAppConfiguration((_, config) =>
         {
diff --git a/server/NeonSprawl.Server.Tests/Game/Skills/MissionRewardDeniedRegistryWebApplicationFactory.cs b/server/NeonSprawl.Server.Tests/Game/Skills/MissionRewardDeniedRegistryWebApplicationFactory.cs
index fb336d1..b4bcd82 100644
--- a/server/NeonSprawl.Server.Tests/Game/Skills/MissionRewardDeniedRegistryWebApplicationFactory.cs
+++ b/server/NeonSprawl.Server.Tests/Game/Skills/MissionRewardDeniedRegistryWebApplicationFactory.cs
@@ -9,6 +9,7 @@ using NeonSprawl.Server.Game.AbilityInput;
 using NeonSprawl.Server.Game.Combat;
 using NeonSprawl.Server.Game.Crafting;
 using NeonSprawl.Server.Game.Mastery;
+using NeonSprawl.Server.Game.Npc;
 using NeonSprawl.Server.Game.PositionState;
 using NeonSprawl.Server.Game.Skills;
 using Npgsql;
@@ -37,10 +38,14 @@ public sealed class MissionRewardDeniedRegistryWebApplicationFactory : WebApplic
         var abilitiesDir = AbilityCatalogPathResolution.TryDiscoverAbilitiesDirectory(AppContext.BaseDirectory)
             ?? throw new InvalidOperationException(
                 "Could not discover repo content/abilities from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
+        var npcBehaviorsDir = NpcBehaviorCatalogPathResolution.TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory)
+            ?? throw new InvalidOperationException(
+                "Could not discover repo content/npc-behaviors from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
         builder.UseSetting("Content:SkillsDirectory", skillsDir);
         builder.UseSetting("Content:MasteryDirectory", masteryDir);
         builder.UseSetting("Content:RecipesDirectory", recipesDir);
         builder.UseSetting("Content:AbilitiesDirectory", abilitiesDir);
+        builder.UseSetting("Content:NpcBehaviorsDirectory", npcBehaviorsDir);
 
         builder.ConfigureTestServices(services =>
         {
diff --git a/server/NeonSprawl.Server.Tests/Game/Skills/RefineActivityDeniedRegistryWebApplicationFactory.cs b/server/NeonSprawl.Server.Tests/Game/Skills/RefineActivityDeniedRegistryWebApplicationFactory.cs
index b0b9a23..5d46c3e 100644
--- a/server/NeonSprawl.Server.Tests/Game/Skills/RefineActivityDeniedRegistryWebApplicationFactory.cs
+++ b/server/NeonSprawl.Server.Tests/Game/Skills/RefineActivityDeniedRegistryWebApplicationFactory.cs
@@ -9,6 +9,7 @@ using NeonSprawl.Server.Game.AbilityInput;
 using NeonSprawl.Server.Game.Combat;
 using NeonSprawl.Server.Game.Crafting;
 using NeonSprawl.Server.Game.Mastery;
+using NeonSprawl.Server.Game.Npc;
 using NeonSprawl.Server.Game.PositionState;
 using NeonSprawl.Server.Game.Skills;
 using Npgsql;
@@ -37,10 +38,14 @@ public sealed class RefineActivityDeniedRegistryWebApplicationFactory : WebAppli
         var abilitiesDir = AbilityCatalogPathResolution.TryDiscoverAbilitiesDirectory(AppContext.BaseDirectory)
             ?? throw new InvalidOperationException(
                 "Could not discover repo content/abilities from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
+        var npcBehaviorsDir = NpcBehaviorCatalogPathResolution.TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory)
+            ?? throw new InvalidOperationException(
+                "Could not discover repo content/npc-behaviors from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
         builder.UseSetting("Content:SkillsDirectory", skillsDir);
         builder.UseSetting("Content:MasteryDirectory", masteryDir);
         builder.UseSetting("Content:RecipesDirectory", recipesDir);
         builder.UseSetting("Content:AbilitiesDirectory", abilitiesDir);
+        builder.UseSetting("Content:NpcBehaviorsDirectory", npcBehaviorsDir);
 
         builder.ConfigureTestServices(services =>
         {
diff --git a/server/NeonSprawl.Server.Tests/InMemoryWebApplicationFactory.cs b/server/NeonSprawl.Server.Tests/InMemoryWebApplicationFactory.cs
index 65b2821..52b36c9 100644
--- a/server/NeonSprawl.Server.Tests/InMemoryWebApplicationFactory.cs
+++ b/server/NeonSprawl.Server.Tests/InMemoryWebApplicationFactory.cs
@@ -12,6 +12,7 @@ using NeonSprawl.Server.Game.Gigs;
 using NeonSprawl.Server.Game.Items;
 using NeonSprawl.Server.Game.PositionState;
 using NeonSprawl.Server.Game.Mastery;
+using NeonSprawl.Server.Game.Npc;
 using NeonSprawl.Server.Game.Skills;
 using Npgsql;
 
@@ -47,12 +48,16 @@ public sealed class InMemoryWebApplicationFactory : WebApplicationFactory<Progra
         var abilitiesDir = AbilityCatalogPathResolution.TryDiscoverAbilitiesDirectory(AppContext.BaseDirectory)
             ?? throw new InvalidOperationException(
                 "Could not discover repo content/abilities from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
+        var npcBehaviorsDir = NpcBehaviorCatalogPathResolution.TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory)
+            ?? throw new InvalidOperationException(
+                "Could not discover repo content/npc-behaviors from AppContext.BaseDirectory; run tests from the neon-sprawl clone.");
         builder.UseSetting("Content:SkillsDirectory", skillsDir);
         builder.UseSetting("Content:MasteryDirectory", masteryDir);
         builder.UseSetting("Content:ItemsDirectory", itemsDir);
         builder.UseSetting("Content:ResourceNodesDirectory", resourceNodesDir);
         builder.UseSetting("Content:RecipesDirectory", recipesDir);
         builder.UseSetting("Content:AbilitiesDirectory", abilitiesDir);
+        builder.UseSetting("Content:NpcBehaviorsDirectory", npcBehaviorsDir);
         builder.UseSetting("Game:EnableMasteryFixtureApi", "true");
 
         builder.ConfigureTestServices(services =>
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogPathResolution.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogPathResolution.cs
new file mode 100644
index 0000000..15e59fe
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogPathResolution.cs
@@ -0,0 +1,60 @@
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>Resolves NPC behavior catalog paths for local dev, tests, and container layouts (NEO-88).</summary>
+public static class NpcBehaviorCatalogPathResolution
+{
+    /// <summary>Walks <paramref name="startDirectory"/> and parents for an existing <c>content/npc-behaviors</c> directory.</summary>
+    public static string? TryDiscoverNpcBehaviorsDirectory(string startDirectory)
+    {
+        for (var dir = new DirectoryInfo(startDirectory); dir is not null; dir = dir.Parent)
+        {
+            var candidate = Path.Combine(dir.FullName, "content", "npc-behaviors");
+            if (Directory.Exists(candidate))
+                return Path.GetFullPath(candidate);
+        }
+
+        return null;
+    }
+
+    /// <summary>
+    /// Resolves the npc-behaviors catalog directory.
+    /// Empty <paramref name="configuredNpcBehaviorsDirectory"/> triggers discovery from <see cref="AppContext.BaseDirectory"/>.
+    /// </summary>
+    public static string ResolveNpcBehaviorsDirectory(string? configuredNpcBehaviorsDirectory, string contentRootPath)
+    {
+        if (string.IsNullOrWhiteSpace(configuredNpcBehaviorsDirectory))
+        {
+            var discovered = TryDiscoverNpcBehaviorsDirectory(AppContext.BaseDirectory);
+            if (discovered is not null)
+                return discovered;
+
+            throw new InvalidOperationException(
+                "Content:NpcBehaviorsDirectory is not set and auto-discovery failed (no ancestor of AppContext.BaseDirectory contains 'content/npc-behaviors'). " +
+                "Set Content:NpcBehaviorsDirectory in configuration or environment (e.g. Content__NpcBehaviorsDirectory).");
+        }
+
+        var trimmed = configuredNpcBehaviorsDirectory.Trim();
+        if (Path.IsPathRooted(trimmed))
+            return Path.GetFullPath(trimmed);
+
+        return Path.GetFullPath(Path.Combine(contentRootPath, trimmed));
+    }
+
+    /// <summary>Resolves JSON Schema path for a single NPC behavior row (Draft 2020-12).</summary>
+    public static string ResolveNpcBehaviorDefSchemaPath(
+        string npcBehaviorsDirectory,
+        string? configuredSchemaPath,
+        string contentRootPath)
+    {
+        if (!string.IsNullOrWhiteSpace(configuredSchemaPath))
+        {
+            var trimmed = configuredSchemaPath.Trim();
+            if (Path.IsPathRooted(trimmed))
+                return Path.GetFullPath(trimmed);
+
+            return Path.GetFullPath(Path.Combine(contentRootPath, trimmed));
+        }
+
+        return Path.GetFullPath(Path.Combine(npcBehaviorsDirectory, "..", "schemas", "npc-behavior-def.schema.json"));
+    }
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs
new file mode 100644
index 0000000..9f16625
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorCatalogServiceCollectionExtensions.cs
@@ -0,0 +1,37 @@
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Options;
+using NeonSprawl.Server.Game.Skills;
+
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>DI registration for the fail-fast NPC behavior catalog (NEO-88).</summary>
+public static class NpcBehaviorCatalogServiceCollectionExtensions
+{
+    /// <summary>Binds <see cref="ContentPathsOptions"/> and registers <see cref="NpcBehaviorDefinitionCatalog"/> as a singleton.</summary>
+    public static IServiceCollection AddNpcBehaviorDefinitionCatalog(this IServiceCollection services, IConfiguration configuration)
+    {
+        services.AddOptions<ContentPathsOptions>()
+            .Bind(configuration.GetSection(ContentPathsOptions.SectionName));
+
+        services.AddSingleton<NpcBehaviorDefinitionCatalog>(sp =>
+        {
+            var hostEnv = sp.GetRequiredService<IHostEnvironment>();
+            var opts = sp.GetRequiredService<IOptions<ContentPathsOptions>>().Value;
+            var logger = sp.GetRequiredService<ILoggerFactory>()
+                .CreateLogger("NeonSprawl.Server.Game.Npc.NpcBehaviorCatalog");
+
+            var npcBehaviorsDir = NpcBehaviorCatalogPathResolution.ResolveNpcBehaviorsDirectory(
+                opts.NpcBehaviorsDirectory,
+                hostEnv.ContentRootPath);
+            var schemaPath = NpcBehaviorCatalogPathResolution.ResolveNpcBehaviorDefSchemaPath(
+                npcBehaviorsDir,
+                opts.NpcBehaviorDefSchemaPath,
+                hostEnv.ContentRootPath);
+
+            return NpcBehaviorDefinitionCatalogLoader.Load(npcBehaviorsDir, schemaPath, logger);
+        });
+
+        return services;
+    }
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefRow.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefRow.cs
new file mode 100644
index 0000000..1f93d9a
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefRow.cs
@@ -0,0 +1,13 @@
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>One validated <c>NpcBehaviorDef</c> row from <c>content/npc-behaviors/*_npc_behaviors.json</c> (NEO-88).</summary>
+public sealed record NpcBehaviorDefRow(
+    string Id,
+    string DisplayName,
+    string ArchetypeKind,
+    int MaxHp,
+    double AggroRadius,
+    double LeashRadius,
+    double TelegraphWindupSeconds,
+    int AttackDamage,
+    double AttackCooldownSeconds);
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs
new file mode 100644
index 0000000..14d2264
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalog.cs
@@ -0,0 +1,25 @@
+using System.Collections.ObjectModel;
+
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>In-memory NPC behavior catalog loaded at startup (NEO-88). Game callers should use INpcBehaviorDefinitionRegistry (NEO-89).</summary>
+public sealed class NpcBehaviorDefinitionCatalog(
+    string npcBehaviorsDirectory,
+    IReadOnlyDictionary<string, NpcBehaviorDefRow> byId,
+    int catalogJsonFileCount)
+{
+    /// <summary>Absolute path to the directory that was enumerated for <c>*_npc_behaviors.json</c> catalogs.</summary>
+    public string NpcBehaviorsDirectory { get; } = npcBehaviorsDirectory;
+
+    public IReadOnlyDictionary<string, NpcBehaviorDefRow> ById { get; } =
+        new ReadOnlyDictionary<string, NpcBehaviorDefRow>(new Dictionary<string, NpcBehaviorDefRow>(byId, StringComparer.Ordinal));
+
+    public int DistinctBehaviorCount => ById.Count;
+
+    /// <summary>Number of <c>*_npc_behaviors.json</c> files under <see cref="NpcBehaviorsDirectory"/>.</summary>
+    public int CatalogJsonFileCount { get; } = catalogJsonFileCount;
+
+    /// <summary>Resolves a catalog row by stable behavior <paramref name="id"/>.</summary>
+    public bool TryGetBehavior(string id, out NpcBehaviorDefRow? row) =>
+        ById.TryGetValue(id, out row);
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalogLoader.cs b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalogLoader.cs
new file mode 100644
index 0000000..be7cddd
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/NpcBehaviorDefinitionCatalogLoader.cs
@@ -0,0 +1,208 @@
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using Json.Schema;
+using Microsoft.Extensions.Logging;
+
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>Loads and validates <c>content/npc-behaviors/*_npc_behaviors.json</c> using the same rules as <c>scripts/validate_content.py</c> (NEO-88).</summary>
+public static class NpcBehaviorDefinitionCatalogLoader
+{
+    /// <summary>Loads catalogs from disk or throws <see cref="InvalidOperationException"/> with actionable messages.</summary>
+    public static NpcBehaviorDefinitionCatalog Load(string npcBehaviorsDirectory, string schemaPath, ILogger logger)
+    {
+        npcBehaviorsDirectory = Path.GetFullPath(npcBehaviorsDirectory);
+        schemaPath = Path.GetFullPath(schemaPath);
+
+        var errors = new List<string>();
+
+        if (!File.Exists(schemaPath))
+            errors.Add($"error: missing schema file {schemaPath}");
+
+        if (!Directory.Exists(npcBehaviorsDirectory))
+            errors.Add($"error: missing directory {npcBehaviorsDirectory}");
+
+        if (errors.Count > 0)
+            ThrowIfAny(errors);
+
+        var jsonFiles = Directory.GetFiles(npcBehaviorsDirectory, "*_npc_behaviors.json", SearchOption.TopDirectoryOnly)
+            .OrderBy(p => p, StringComparer.Ordinal)
+            .ToArray();
+        if (jsonFiles.Length == 0)
+            errors.Add($"error: no *_npc_behaviors.json files under {npcBehaviorsDirectory}");
+
+        if (errors.Count > 0)
+            ThrowIfAny(errors);
+
+        var schema = JsonSchema.FromText(File.ReadAllText(schemaPath));
+        var evalOptions = new EvaluationOptions { OutputFormat = OutputFormat.List };
+
+        var behaviorIdToSourceFile = new Dictionary<string, string>(StringComparer.Ordinal);
+        var rows = new Dictionary<string, NpcBehaviorDefRow>(StringComparer.Ordinal);
+
+        foreach (var path in jsonFiles)
+        {
+            JsonNode? root;
+            try
+            {
+                root = JsonNode.Parse(File.ReadAllText(path));
+            }
+            catch (JsonException ex)
+            {
+                errors.Add($"error: {path}: invalid JSON: {ex.Message}");
+                continue;
+            }
+
+            if (root is not JsonObject rootObj)
+            {
+                errors.Add($"error: {path}: expected JSON object at root");
+                continue;
+            }
+
+            var schemaVersionNode = rootObj["schemaVersion"];
+            if (schemaVersionNode is not JsonValue schemaVersionValue ||
+                !schemaVersionValue.TryGetValue<int>(out var schemaVersion) ||
+                schemaVersion != 1)
+            {
+                var got = schemaVersionNode?.ToJsonString() ?? "null";
+                errors.Add($"error: {path}: expected schemaVersion 1, got {got}");
+                continue;
+            }
+
+            var npcBehaviorsNode = rootObj["npcBehaviors"];
+            if (npcBehaviorsNode is not JsonArray npcBehaviorsArray)
+            {
+                errors.Add($"error: {path}: expected top-level 'npcBehaviors' array");
+                continue;
+            }
+
+            for (var i = 0; i < npcBehaviorsArray.Count; i++)
+            {
+                var behavior = npcBehaviorsArray[i];
+                if (behavior is not JsonObject rowObj)
+                {
+                    errors.Add($"error: {path}: npcBehaviors[{i}] must be an object");
+                    continue;
+                }
+
+                var eval = schema.Evaluate(rowObj, evalOptions);
+                var schemaMsgs = CollectSchemaMessages(eval, path, i).OrderBy(m => m, StringComparer.Ordinal).ToList();
+                if (!eval.IsValid)
+                {
+                    if (schemaMsgs.Count == 0)
+                        schemaMsgs.Add($"error: {path} npcBehaviors[{i}] (root): schema validation failed");
+
+                    errors.AddRange(schemaMsgs);
+                }
+
+                var rowSchemaErrors = schemaMsgs.Count;
+
+                var bid = (rowObj["id"] as JsonValue)?.GetValue<string>();
+                if (bid is not null && rowSchemaErrors == 0)
+                {
+                    if (behaviorIdToSourceFile.TryGetValue(bid, out var prevPath))
+                    {
+                        errors.Add($"error: duplicate npc behavior id '{bid}' in {prevPath} and {path}");
+                        continue;
+                    }
+
+                    behaviorIdToSourceFile[bid] = path;
+                    rows[bid] = ParseRow(rowObj);
+                }
+            }
+        }
+
+        ThrowIfAny(errors);
+
+        var e5m2 = PrototypeE5M2NpcBehaviorCatalogRules.TryGetE5M2GateError(behaviorIdToSourceFile);
+        if (e5m2 is not null)
+        {
+            errors.Add(e5m2);
+            ThrowIfAny(errors);
+        }
+
+        var numeric = PrototypeE5M2NpcBehaviorCatalogRules.TryGetNumericGateError(rows);
+        if (numeric is not null)
+        {
+            errors.Add(numeric);
+            ThrowIfAny(errors);
+        }
+
+        if (logger.IsEnabled(LogLevel.Information))
+        {
+            logger.LogInformation(
+                "Loaded NPC behavior catalog from {NpcBehaviorsDirectory}: {BehaviorCount} behavior(s) across {CatalogFileCount} JSON catalog file(s).",
+                npcBehaviorsDirectory,
+                rows.Count,
+                jsonFiles.Length);
+        }
+
+        return new NpcBehaviorDefinitionCatalog(npcBehaviorsDirectory, rows, jsonFiles.Length);
+    }
+
+    private static NpcBehaviorDefRow ParseRow(JsonObject rowObj)
+    {
+        var id = (rowObj["id"] as JsonValue)!.GetValue<string>();
+        var displayName = (rowObj["displayName"] as JsonValue)!.GetValue<string>();
+        var archetypeKind = (rowObj["archetypeKind"] as JsonValue)!.GetValue<string>();
+        var maxHp = (rowObj["maxHp"] as JsonValue)!.GetValue<int>();
+        var aggroRadius = (rowObj["aggroRadius"] as JsonValue)!.GetValue<double>();
+        var leashRadius = (rowObj["leashRadius"] as JsonValue)!.GetValue<double>();
+        var telegraphWindupSeconds = (rowObj["telegraphWindupSeconds"] as JsonValue)!.GetValue<double>();
+        var attackDamage = (rowObj["attackDamage"] as JsonValue)!.GetValue<int>();
+        var attackCooldownSeconds = (rowObj["attackCooldownSeconds"] as JsonValue)!.GetValue<double>();
+
+        return new NpcBehaviorDefRow(
+            id,
+            displayName,
+            archetypeKind,
+            maxHp,
+            aggroRadius,
+            leashRadius,
+            telegraphWindupSeconds,
+            attackDamage,
+            attackCooldownSeconds);
+    }
+
+    private static List<string> CollectSchemaMessages(EvaluationResults eval, string filePath, int index)
+    {
+        var sink = new List<string>();
+        AppendSchemaMessages(eval, filePath, index, sink);
+        return sink;
+    }
+
+    private static void AppendSchemaMessages(EvaluationResults r, string filePath, int index, List<string> sink)
+    {
+        if (r.HasDetails)
+        {
+            foreach (var d in r.Details!)
+                AppendSchemaMessages(d, filePath, index, sink);
+        }
+
+        if (!r.HasErrors)
+            return;
+
+        foreach (var kv in r.Errors!)
+        {
+            var loc = r.InstanceLocation?.ToString();
+            if (string.IsNullOrEmpty(loc) || loc == "#")
+                loc = "(root)";
+
+            sink.Add($"error: {filePath} npcBehaviors[{index}] {loc}: {kv.Key} — {kv.Value}");
+        }
+    }
+
+    private static void ThrowIfAny(List<string> errors)
+    {
+        if (errors.Count == 0)
+            return;
+
+        var sb = new StringBuilder();
+        sb.AppendLine("NPC behavior catalog validation failed:");
+        foreach (var e in errors.OrderBy(x => x, StringComparer.Ordinal))
+            sb.AppendLine(e);
+
+        throw new InvalidOperationException(sb.ToString().TrimEnd());
+    }
+}
diff --git a/server/NeonSprawl.Server/Game/Npc/PrototypeE5M2NpcBehaviorCatalogRules.cs b/server/NeonSprawl.Server/Game/Npc/PrototypeE5M2NpcBehaviorCatalogRules.cs
new file mode 100644
index 0000000..3bb2de9
--- /dev/null
+++ b/server/NeonSprawl.Server/Game/Npc/PrototypeE5M2NpcBehaviorCatalogRules.cs
@@ -0,0 +1,50 @@
+using System.Collections.Frozen;
+
+namespace NeonSprawl.Server.Game.Npc;
+
+/// <summary>
+/// Prototype E5M2 roster + numeric gates (NEO-87 / NEO-88), mirrored from <c>scripts/validate_content.py</c>
+/// <c>PROTOTYPE_E5M2_NPC_BEHAVIOR_IDS</c>, <c>_prototype_e5m2_npc_behavior_gate</c>, and
+/// <c>_prototype_e5m2_npc_behavior_numeric_gate</c>.
+/// </summary>
+public static class PrototypeE5M2NpcBehaviorCatalogRules
+{
+    /// <summary>Keep in sync with <c>scripts/validate_content.py</c> <c>PROTOTYPE_E5M2_NPC_BEHAVIOR_IDS</c>.</summary>
+    public static readonly FrozenSet<string> ExpectedBehaviorIds = FrozenSet.ToFrozenSet(
+        [
+            "prototype_melee_pressure",
+            "prototype_ranged_control",
+            "prototype_elite_mini_boss",
+        ],
+        StringComparer.Ordinal);
+
+    /// <summary>Returns a human-readable error if the E5M2 behavior contract fails, otherwise <see langword="null"/>.</summary>
+    public static string? TryGetE5M2GateError(IReadOnlyDictionary<string, string> behaviorIdToSourceFile)
+    {
+        var ids = behaviorIdToSourceFile.Keys.ToFrozenSet(StringComparer.Ordinal);
+        if (!ids.SetEquals(ExpectedBehaviorIds))
+        {
+            return
+                "error: prototype E5M2 expects exactly npc behavior ids " +
+                $"[{string.Join(", ", ExpectedBehaviorIds.Order(StringComparer.Ordinal).Select(s => "'" + s + "'"))}], " +
+                $"got [{string.Join(", ", ids.Order(StringComparer.Ordinal).Select(s => "'" + s + "'"))}]";
+        }
+
+        return null;
+    }
+
+    /// <summary>Returns a human-readable error when <c>leashRadius &lt;= aggroRadius</c>, otherwise <see langword="null"/>.</summary>
+    public static string? TryGetNumericGateError(IReadOnlyDictionary<string, NpcBehaviorDefRow> rowsById)
+    {
+        foreach (var (bid, row) in rowsById)
+        {
+            if (row.LeashRadius <= row.AggroRadius)
+            {
+                return
+                    $"error: npc behavior '{bid}': leashRadius {row.LeashRadius} must be > aggroRadius {row.AggroRadius}";
+            }
+        }
+
+        return null;
+    }
+}
diff --git a/server/NeonSprawl.Server/Game/Skills/ContentPathsOptions.cs b/server/NeonSprawl.Server/Game/Skills/ContentPathsOptions.cs
index 93da821..d04a590 100644
--- a/server/NeonSprawl.Server/Game/Skills/ContentPathsOptions.cs
+++ b/server/NeonSprawl.Server/Game/Skills/ContentPathsOptions.cs
@@ -88,4 +88,16 @@ public sealed class ContentPathsOptions
     /// When unset, resolved as <c>{parent of abilities directory}/schemas/ability-def.schema.json</c>.
     /// </summary>
     public string? AbilityDefSchemaPath { get; set; }
+
+    /// <summary>
+    /// Optional. Absolute path, or path relative to <see cref="Microsoft.Extensions.Hosting.IHostEnvironment.ContentRootPath"/>.
+    /// When unset, the host walks ancestors of <see cref="AppContext.BaseDirectory"/> for a <c>content/npc-behaviors</c> directory.
+    /// </summary>
+    public string? NpcBehaviorsDirectory { get; set; }
+
+    /// <summary>
+    /// Optional override for <c>npc-behavior-def.schema.json</c>.
+    /// When unset, resolved as <c>{parent of npc-behaviors directory}/schemas/npc-behavior-def.schema.json</c>.
+    /// </summary>
+    public string? NpcBehaviorDefSchemaPath { get; set; }
 }
diff --git a/server/NeonSprawl.Server/Program.cs b/server/NeonSprawl.Server/Program.cs
index f10b458..d3b7020 100644
--- a/server/NeonSprawl.Server/Program.cs
+++ b/server/NeonSprawl.Server/Program.cs
@@ -6,6 +6,7 @@ using NeonSprawl.Server.Game.Gigs;
 using NeonSprawl.Server.Game.Interaction;
 using NeonSprawl.Server.Game.Items;
 using NeonSprawl.Server.Game.Mastery;
+using NeonSprawl.Server.Game.Npc;
 using NeonSprawl.Server.Game.PositionState;
 using NeonSprawl.Server.Game.Skills;
 using NeonSprawl.Server.Game.Targeting;
@@ -23,6 +24,7 @@ builder.Services.AddItemDefinitionCatalog(builder.Configuration);
 builder.Services.AddResourceNodeCatalog(builder.Configuration);
 builder.Services.AddRecipeDefinitionCatalog(builder.Configuration);
 builder.Services.AddAbilityDefinitionCatalog(builder.Configuration);
+builder.Services.AddNpcBehaviorDefinitionCatalog(builder.Configuration);
 builder.Services.AddMasteryCatalog(builder.Configuration);
 
 var app = builder.Build();
@@ -31,6 +33,7 @@ _ = app.Services.GetRequiredService<ItemDefinitionCatalog>();
 _ = app.Services.GetRequiredService<ResourceNodeCatalog>();
 _ = app.Services.GetRequiredService<RecipeDefinitionCatalog>();
 _ = app.Services.GetRequiredService<AbilityDefinitionCatalog>();
+_ = app.Services.GetRequiredService<NpcBehaviorDefinitionCatalog>();
 _ = app.Services.GetRequiredService<MasteryCatalog>();
 _ = app.Services.GetRequiredService<ISkillLevelCurve>();
 
diff --git a/server/NeonSprawl.Server/appsettings.json b/server/NeonSprawl.Server/appsettings.json
index b13ffb7..313e931 100644
--- a/server/NeonSprawl.Server/appsettings.json
+++ b/server/NeonSprawl.Server/appsettings.json
@@ -15,7 +15,9 @@
     "RecipeDefSchemaPath": "",
     "RecipeIoRowSchemaPath": "",
     "AbilitiesDirectory": "",
-    "AbilityDefSchemaPath": ""
+    "AbilityDefSchemaPath": "",
+    "NpcBehaviorsDirectory": "",
+    "NpcBehaviorDefSchemaPath": ""
   },
   "Game": {
     "DevPlayerId": "dev-local-1",
diff --git a/server/README.md b/server/README.md
index aeda2c6..ab9a4e9 100644
--- a/server/README.md
+++ b/server/README.md
@@ -93,6 +93,19 @@ On startup the host loads every **`*_abilities.json`** under the abilities direc
 
 On success, **Information** logs include the resolved abilities directory path, distinct ability count, and catalog file count. Game code should use **`IAbilityDefinitionRegistry`** for lookups (NEO-79). The catalog singleton remains for fail-fast startup only; do not inject **`AbilityDefinitionCatalog`** in new game code. Hotbar loadout and ability cast routes validate ability ids via **`IAbilityDefinitionRegistry.TryNormalizeKnown`** (backed by the loaded catalog, not a separate static allowlist).
 
+## NPC behavior catalog (`content/npc-behaviors`, NEO-88)
+
+On startup the host loads every **`*_npc_behaviors.json`** under the npc-behaviors directory, validates each row against **`content/schemas/npc-behavior-def.schema.json`**, requires **`schemaVersion` 1** per file, rejects **duplicate `id`** values across files, enforces the **prototype E5M2** three-id roster gate, and requires **`leashRadius > aggroRadius`** per row (same rules as **`scripts/validate_content.py`**). If anything is missing or invalid, the process **exits during startup** with an actionable error—there is no silent fallback.
+
+| Config | Meaning |
+|--------|---------|
+| **`Content:NpcBehaviorsDirectory`** | Optional. Absolute path, or path relative to the server **content root**. When unset, walks **ancestors of `AppContext.BaseDirectory`** until it finds **`content/npc-behaviors`**. |
+| **`Content:NpcBehaviorDefSchemaPath`** | Optional override for **`npc-behavior-def.schema.json`**. When unset, **`{parent of npc-behaviors directory}/schemas/npc-behavior-def.schema.json`**. |
+
+**Docker / CI:** include **`content/npc-behaviors`** and **`content/schemas/npc-behavior-def.schema.json`** in the mounted **`content/`** tree; set **`Content__NpcBehaviorsDirectory`** when layout differs.
+
+On success, **Information** logs include the resolved npc-behaviors directory path, distinct behavior count, and catalog file count. Game code should use **`INpcBehaviorDefinitionRegistry`** for lookups (NEO-89). The catalog singleton remains for fail-fast startup only; do not inject **`NpcBehaviorDefinitionCatalog`** in new game code.
+
 ## Ability definitions (NEO-78)
 
 **`GET /game/world/ability-definitions`** returns a versioned JSON body (`schemaVersion` **1**, **`abilities`**) backed by **`IAbilityDefinitionRegistry`** — the same prototype rows loaded at startup (no second source of truth). Each row includes **`id`**, **`displayName`**, **`baseDamage`**, **`cooldownSeconds`**, and **`abilityKind`** when present in content. Plan: [NEO-78 implementation plan](../../docs/plans/NEO-78-implementation-plan.md); Bruno: `bruno/neon-sprawl-server/ability-definitions/`.