diff --git a/CHANGELOG.md b/CHANGELOG.md
index b9c456ff..fe90deb5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@
 
 ### Fixed
 
+- Clarified `debug_attach_sim` PID attach arguments so the schema documents that `pid` must be used without `bundleId` or `waitFor`, and invalid `pid` + `waitFor: true` calls now fail validation before LLDB is invoked ([#417](https://github.com/getsentry/XcodeBuildMCP/issues/417)).
 - Fixed Claude UI benchmark preflight so transient malformed or still-loading UI snapshots no longer crash the harness or finish before app UI is observable.
 - Fixed Claude UI benchmark preflight so configured first-run dismissals require a concrete simulator ID, suite-provided simulator IDs are recorded in command logs, and preflight-launched apps are terminated after post-launch failures.
 - Fixed Claude UI benchmark config handling so invalid `failurePatterns` regexes and runtime-incompatible `sessionDefaults` fail before a suite starts and partial `allowedVariance` overrides preserve defaults for omitted metrics.
diff --git a/src/mcp/tools/debugging/__tests__/debugging-tools.test.ts b/src/mcp/tools/debugging/__tests__/debugging-tools.test.ts
index 331456b7..2f6f6968 100644
--- a/src/mcp/tools/debugging/__tests__/debugging-tools.test.ts
+++ b/src/mcp/tools/debugging/__tests__/debugging-tools.test.ts
@@ -126,6 +126,12 @@ describe('debug_attach_sim', () => {
     it('should expose schema with expected shape', () => {
       expect(attachSchema).toBeDefined();
     });
+
+    it('documents PID attach argument constraints in the public schema', () => {
+      expect(attachSchema.pid.description).toContain('without bundleId');
+      expect(attachSchema.pid.description).toContain('without waitFor');
+      expect(attachSchema.waitFor.description).toContain('Only valid when attaching by bundleId');
+    });
   });
 
   describe('Handler Requirements', () => {
@@ -171,6 +177,34 @@ describe('debug_attach_sim', () => {
       expect(text).toContain('bundleId');
       expect(text).toContain('pid');
     });
+
+    it('rejects waitFor true when attaching by pid', async () => {
+      __setTestDebuggerToolContextOverride(createTestContext());
+      sessionStore.setDefaults({ simulatorId: 'test-sim-uuid' });
+
+      const result = await callHandler(attachHandler, {
+        pid: 1234,
+        waitFor: true,
+      });
+
+      expect(result.isError).toBe(true);
+      const text = result.content[0].text;
+      expect(text).toContain('waitFor is only valid when attaching by bundleId');
+      expect(text).toContain('For PID attach, omit waitFor or set it to false');
+    });
+
+    it('allows waitFor false when attaching by pid', async () => {
+      __setTestDebuggerToolContextOverride(createTestContext());
+      sessionStore.setDefaults({ simulatorId: 'test-sim-uuid' });
+
+      const result = await callHandler(attachHandler, {
+        pid: 1234,
+        waitFor: false,
+      });
+
+      expect(result.isError).toBeFalsy();
+      expect(result.content[0].text).toContain('Attached');
+    });
   });
 
   describe('Logic Behavior', () => {
diff --git a/src/mcp/tools/debugging/debug_attach_sim.ts b/src/mcp/tools/debugging/debug_attach_sim.ts
index b2360cea..e4fb801b 100644
--- a/src/mcp/tools/debugging/debug_attach_sim.ts
+++ b/src/mcp/tools/debugging/debug_attach_sim.ts
@@ -19,6 +19,9 @@ import {
   type DebuggerToolContext,
 } from '../../../utils/debugger/index.ts';
 
+const DEBUG_ATTACH_MODE_HELP =
+  'Valid attach modes: provide bundleId without pid, or provide pid without bundleId and omit waitFor or set waitFor to false.';
+
 const baseSchemaObject = z.object({
   simulatorId: z
     .string()
@@ -32,9 +35,26 @@ const baseSchemaObject = z.object({
     .describe(
       "Name of the simulator (e.g., 'iPhone 17'). Provide EITHER this OR simulatorId, not both",
     ),
-  bundleId: z.string().optional(),
-  pid: z.number().int().positive().optional(),
-  waitFor: z.boolean().optional().describe('Wait for the process to appear when attaching'),
+  bundleId: z
+    .string()
+    .optional()
+    .describe(
+      'Attach by bundle identifier. Provide bundleId without pid; waitFor may be used with this mode.',
+    ),
+  pid: z
+    .number()
+    .int()
+    .positive()
+    .optional()
+    .describe(
+      'Attach to an already-running process by PID. Provide pid without bundleId and without waitFor.',
+    ),
+  waitFor: z
+    .boolean()
+    .optional()
+    .describe(
+      'Only valid when attaching by bundleId. For PID attach, omit waitFor or set it to false.',
+    ),
   continueOnAttach: z.boolean().optional().default(true).describe('default: true'),
   makeCurrent: z
     .boolean()
@@ -47,10 +67,14 @@ const debugAttachSchema = z.preprocess(
   nullifyEmptyStrings,
   withSimulatorIdOrName(baseSchemaObject)
     .refine((val) => val.bundleId !== undefined || val.pid !== undefined, {
-      message: 'Provide either bundleId or pid to attach.',
+      message: `Provide either bundleId or pid to attach. ${DEBUG_ATTACH_MODE_HELP}`,
     })
     .refine((val) => !(val.bundleId && val.pid), {
-      message: 'bundleId and pid are mutually exclusive. Provide only one.',
+      message: 'Provide either bundleId or pid, not both.',
+    })
+    .refine((val) => !(val.pid !== undefined && val.waitFor === true), {
+      message:
+        'waitFor is only valid when attaching by bundleId. For PID attach, omit waitFor or set it to false.',
     }),
 );