fix(core): Preserve mixed-case slug parameters (#1142)

Preserve caller casing for Sentry resource slug parameters instead of
lowercasing them during MCP argument parsing.

Sentry slug lookups can be exact on legacy self-hosted instances, so
mixed-case organization, project, and team slugs need to reach Sentry
API paths unchanged. This restores compatibility for installs that still
have mixed-case slugs.

The change keeps trimming and slug validation, leaves non-slug
normalization in place, and updates the generated tool definition copy
for the exact lowercase `all` sentinel. Regression coverage now asserts
mixed-case parser output and API request paths/bodies for the affected
tools.

Fixes #1138

Co-authored-by: GPT-5 Codex <noreply@openai.com>

Author: dcramer

docs/contributing/documentation-style-guide.md

@@ -81,7 +81,6 @@ Link to reusable patterns: See "Error Handling" in [Common Patterns](common-patt
 // Tool parameter pattern used throughout the codebase
 export const ParamOrganizationSlug = z
   .string()
-  .toLowerCase()
   .trim()
   .describe("The organization's slug. Find using `find_organizations()` tool.");
 ```
@@ -93,10 +92,9 @@ import { z } from "zod";
 
 // Define a schema for the organization slug parameter
 // This schema will validate that the input is a string
-// It will also convert to lowercase and trim whitespace
+// It will also trim whitespace
 export const ParamOrganizationSlug = z
   .string() // Ensures the value is a string
-  .toLowerCase() // Converts to lowercase
   .trim() // Removes whitespace
   .describe("The organization's slug..."); // Adds description
 ```

packages/mcp-core/src/schema.ts

@@ -2,16 +2,17 @@
  * Reusable Zod parameter schemas for MCP tools.
  *
  * Shared validation schemas used across tool definitions to ensure consistent
- * parameter handling and validation. Each schema includes transformation
- * (e.g., toLowerCase, trim) and LLM-friendly descriptions.
+ * parameter handling and validation. Schemas apply minimal normalization
+ * (e.g., trim) and LLM-friendly descriptions.
  */
 import { z } from "zod";
 import { SENTRY_GUIDES } from "./constants";
 import { validateSlug } from "./utils/slug-validation";
 
+// Sentry slug lookups can be exact and case-sensitive on legacy instances.
+// Preserve caller casing for resource slugs; only trim and validate shape.
 export const ParamOrganizationSlug = z
   .string()
-  .toLowerCase()
   .trim()
   .superRefine(validateSlug)
   .describe(
@@ -20,7 +21,6 @@ export const ParamOrganizationSlug = z
 
 export const ParamTeamSlug = z
   .string()
-  .toLowerCase()
   .trim()
   .superRefine(validateSlug)
   .describe(
@@ -29,7 +29,6 @@ export const ParamTeamSlug = z
 
 export const ParamProjectSlug = z
   .string()
-  .toLowerCase()
   .trim()
   .superRefine(validateSlug)
   .describe(
@@ -38,11 +37,10 @@ export const ParamProjectSlug = z
 
 export const ParamProjectSlugOrAll = z
   .string()
-  .toLowerCase()
   .trim()
   .superRefine(validateSlug)
   .describe(
-    "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible.",
+    "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug.",
   );
 
 export const ParamSearchQuery = z

packages/mcp-core/src/toolDefinitions.json

@@ -290,13 +290,13 @@
           "anyOf": [
             {
               "type": "string",
-              "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible."
+              "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug."
             },
             {
               "type": "null"
             }
           ],
-          "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible.",
+          "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug.",
           "default": null
         },
         "query": {
@@ -475,13 +475,13 @@
           "anyOf": [
             {
               "type": "string",
-              "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible."
+              "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug."
             },
             {
               "type": "null"
             }
           ],
-          "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible.",
+          "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug.",
           "default": null
         },
         "environment": {
@@ -638,13 +638,13 @@
           "anyOf": [
             {
               "type": "string",
-              "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible."
+              "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug."
             },
             {
               "type": "null"
             }
           ],
-          "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible.",
+          "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug.",
           "default": null
         },
         "query": {
@@ -1197,13 +1197,13 @@
           "anyOf": [
             {
               "type": "string",
-              "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible."
+              "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug."
             },
             {
               "type": "null"
             }
           ],
-          "description": "The project's slug. This will default to all projects you have access to. It is encouraged to specify this when possible.",
+          "description": "The project's slug, or exact lowercase `all` when a tool supports all-projects scope. Other casing is treated as a project slug.",
           "default": null
         },
         "ruleIdOrName": {

packages/mcp-core/src/tools/catalog/find-projects.test.ts

@@ -1,5 +1,8 @@
+import { mswServer } from "@sentry/mcp-server-mocks";
+import { http, HttpResponse } from "msw";
 import { describe, it, expect } from "vitest";
 import findProjects from "./find-projects.js";
+import { prepareToolParams } from "../catalog-runtime/availability";
 import { getServerContext } from "../../test-setup.js";
 
 describe("find_projects", () => {
@@ -19,4 +22,38 @@ describe("find_projects", () => {
       "
     `);
   });
+
+  it("preserves mixed-case organization slug in the API path", async () => {
+    const context = getServerContext();
+
+    mswServer.use(
+      http.get("*/api/0/organizations/*/projects/", ({ request }) => {
+        expect(new URL(request.url).pathname).toBe(
+          "/api/0/organizations/MyOrg/projects/",
+        );
+        return HttpResponse.json([
+          {
+            id: "1",
+            slug: "MyProject",
+            name: "My Project",
+          },
+        ]);
+      }),
+    );
+
+    const params = prepareToolParams({
+      tool: findProjects,
+      params: {
+        organizationSlug: " MyOrg ",
+        regionUrl: null,
+        query: null,
+      },
+      context,
+    }) as Parameters<typeof findProjects.handler>[0];
+
+    const result = await findProjects.handler(params, context);
+
+    expect(result).toContain("# Projects in **MyOrg**");
+    expect(result).toContain("- **MyProject**");
+  });
 });

packages/mcp-core/src/tools/catalog/get-monitor-details.test.ts

@@ -2,6 +2,7 @@ import { mswServer } from "@sentry/mcp-server-mocks";
 import { http, HttpResponse } from "msw";
 import { describe, expect, it } from "vitest";
 import getMonitorDetails from "./get-monitor-details.js";
+import { prepareToolParams } from "../catalog-runtime/availability";
 
 const context = {
   constraints: {
@@ -183,6 +184,69 @@ describe("get_monitor_details", () => {
     ]);
   });
 
+  it("preserves mixed-case project slug in monitor detail endpoints", async () => {
+    const paths: string[] = [];
+    const monitorResponse = {
+      id: "4509100000000001",
+      slug: "nightly-import",
+      name: "Nightly Import",
+      status: "ok",
+      owner: null,
+      project: {
+        id: "4509109104082945",
+        slug: "MyProject",
+        name: "My Project",
+      },
+      config: {
+        schedule_type: "crontab",
+        schedule: ["crontab", "0 2 * * *"],
+      },
+      environments: [],
+    };
+    mswServer.use(
+      http.get(
+        "*/api/0/projects/*/*/monitors/nightly-import/",
+        ({ request }) => {
+          paths.push(new URL(request.url).pathname);
+          return HttpResponse.json(monitorResponse);
+        },
+      ),
+      http.get(
+        "*/api/0/projects/*/*/monitors/nightly-import/checkins/",
+        ({ request }) => {
+          paths.push(new URL(request.url).pathname);
+          return HttpResponse.json([]);
+        },
+      ),
+    );
+
+    const params = prepareToolParams({
+      tool: getMonitorDetails,
+      params: {
+        organizationSlug: " MyOrg ",
+        regionUrl: null,
+        projectSlugOrId: " MyProject ",
+        monitorSlug: "nightly-import",
+        environment: null,
+        period: "24h",
+        start: null,
+        end: null,
+        checkInLimit: 10,
+        includeStats: false,
+        rollupSeconds: null,
+      },
+      context,
+    }) as Parameters<typeof getMonitorDetails.handler>[0];
+
+    const result = await getMonitorDetails.handler(params, context);
+
+    expect(result).toContain("# Monitor Nightly Import in **MyOrg**");
+    expect(paths).toEqual([
+      "/api/0/projects/MyOrg/MyProject/monitors/nightly-import/",
+      "/api/0/projects/MyOrg/MyProject/monitors/nightly-import/checkins/",
+    ]);
+  });
+
   it("uses StatsMixin time parameters for monitor stats", async () => {
     let checkInsRequestUrl: string | null = null;
     let statsRequestUrl: string | null = null;

packages/mcp-core/src/tools/catalog/get-monitor-details.ts

@@ -93,7 +93,6 @@ export default defineTool({
     regionUrl: ParamRegionUrl.nullable().default(null),
     projectSlugOrId: z
       .string()
-      .toLowerCase()
       .trim()
       .superRefine(validateSlugOrId)
       .nullable()

packages/mcp-core/src/tools/catalog/get-release-details.test.ts

@@ -2,6 +2,7 @@ import { mswServer, releaseFixture } from "@sentry/mcp-server-mocks";
 import { http, HttpResponse } from "msw";
 import { describe, expect, it } from "vitest";
 import getReleaseDetails from "./get-release-details.js";
+import { prepareToolParams } from "../catalog-runtime/availability";
 
 const context = {
   constraints: {
@@ -245,6 +246,80 @@ describe("get_release_details", () => {
     );
   });
 
+  it("preserves mixed-case project slug in release detail endpoints", async () => {
+    const requests: Array<{
+      kind: "details" | "deploys" | "commits";
+      url: string;
+    }> = [];
+    const releaseVersion = "8ce89484-0fec-4913-a2cd-e8e2d41dee36";
+    mswServer.use(
+      http.get(
+        `https://sentry.io/api/0/projects/MyOrg/MyProject/releases/${releaseVersion}/`,
+        ({ request }) => {
+          requests.push({ kind: "details", url: request.url });
+          return HttpResponse.json(releaseFixture);
+        },
+      ),
+      http.get(
+        `https://sentry.io/api/0/organizations/MyOrg/releases/${releaseVersion}/deploys/`,
+        ({ request }) => {
+          requests.push({ kind: "deploys", url: request.url });
+          return HttpResponse.json([]);
+        },
+      ),
+      http.get(
+        `https://sentry.io/api/0/projects/MyOrg/MyProject/releases/${releaseVersion}/commits/`,
+        ({ request }) => {
+          requests.push({ kind: "commits", url: request.url });
+          return HttpResponse.json([]);
+        },
+      ),
+    );
+
+    const params = prepareToolParams({
+      tool: getReleaseDetails,
+      params: {
+        organizationSlug: " MyOrg ",
+        regionUrl: null,
+        releaseVersion,
+        projectSlugOrId: " MyProject ",
+        includeHealth: false,
+        includeDeploys: true,
+        includeCommits: true,
+        limit: 10,
+      },
+      context,
+    }) as Parameters<typeof getReleaseDetails.handler>[0];
+
+    await getReleaseDetails.handler(params, context);
+
+    expect(requests).toHaveLength(3);
+    const detailsRequest = requests.find(
+      (request) => request.kind === "details",
+    );
+    const deploysRequest = requests.find(
+      (request) => request.kind === "deploys",
+    );
+    const commitsRequest = requests.find(
+      (request) => request.kind === "commits",
+    );
+    expect(detailsRequest).toBeDefined();
+    expect(deploysRequest).toBeDefined();
+    expect(commitsRequest).toBeDefined();
+    expect(new URL(detailsRequest!.url).pathname).toBe(
+      `/api/0/projects/MyOrg/MyProject/releases/${releaseVersion}/`,
+    );
+    expect(new URL(deploysRequest!.url).pathname).toBe(
+      `/api/0/organizations/MyOrg/releases/${releaseVersion}/deploys/`,
+    );
+    expect(new URL(deploysRequest!.url).searchParams.get("projectSlug")).toBe(
+      "MyProject",
+    );
+    expect(new URL(commitsRequest!.url).pathname).toBe(
+      `/api/0/projects/MyOrg/MyProject/releases/${releaseVersion}/commits/`,
+    );
+  });
+
   it("hides health metadata when includeHealth is false", async () => {
     const releaseVersion = "8ce89484-0fec-4913-a2cd-e8e2d41dee36";
     mswServer.use(

packages/mcp-core/src/tools/catalog/get-release-details.ts

@@ -101,7 +101,6 @@ export default defineTool({
     releaseVersion: z.string().trim().min(1).describe("Exact release version."),
     projectSlugOrId: z
       .string()
-      .toLowerCase()
       .trim()
       .superRefine(validateSlugOrId)
       .describe(