diff --git a/apps/web/src/lib/ai-gateway/api-request-log-errors.ts b/apps/web/src/lib/ai-gateway/api-request-log-errors.ts
index baba9cb3f..197878eda 100644
--- a/apps/web/src/lib/ai-gateway/api-request-log-errors.ts
+++ b/apps/web/src/lib/ai-gateway/api-request-log-errors.ts
@@ -4,12 +4,25 @@ import type Anthropic from '@anthropic-ai/sdk';
 import { createParser } from 'eventsource-parser';
 import type { GatewayRequest } from '@/lib/ai-gateway/providers/openrouter/types';
 
-export const toolCallArgumentErrorSchema = z.object({
-  tool_call_id: z.string(),
-  tool_name: z.string(),
-  kind: z.enum(['unparseable_json', 'schema_mismatch']),
-  details: z.string().optional(),
-});
+export const toolCallArgumentErrorSchema = z.discriminatedUnion('kind', [
+  z.object({
+    tool_call_id: z.string(),
+    tool_name: z.string(),
+    kind: z.literal('unparseable_json'),
+    details: z.string(),
+  }),
+  z.object({
+    tool_call_id: z.string(),
+    tool_name: z.string(),
+    kind: z.literal('schema_mismatch'),
+    details: z.unknown(),
+  }),
+  z.object({
+    tool_call_id: z.string(),
+    tool_name: z.string(),
+    kind: z.literal('unknown_tool'),
+  }),
+]);
 
 export const apiRequestLogErrorSchema = z.object({
   invalid_tool_call_arguments: z.array(toolCallArgumentErrorSchema),
@@ -19,6 +32,21 @@ export type ApiRequestLogError = z.infer<typeof apiRequestLogErrorSchema>;
 
 type ToolCallError = z.infer<typeof toolCallArgumentErrorSchema>;
 
+function checkKnownTool(
+  knownToolNames: Set<string>,
+  toolCallId: string,
+  toolName: string,
+  errors: ToolCallError[]
+): boolean {
+  if (knownToolNames.has(toolName)) return true;
+  errors.push({
+    tool_call_id: toolCallId,
+    tool_name: toolName,
+    kind: 'unknown_tool',
+  });
+  return false;
+}
+
 function validateAgainstSchema(
   parsedArgs: unknown,
   parameters: unknown,
@@ -40,7 +68,7 @@ function validateAgainstSchema(
       tool_call_id: toolCallId,
       tool_name: toolName,
       kind: 'schema_mismatch',
-      details: result.error.message,
+      details: z.treeifyError(result.error),
     });
   }
 }
@@ -86,8 +114,10 @@ function detectChatCompletionSseErrors(
   tools: OpenAI.Chat.ChatCompletionTool[] | null | undefined
 ): ToolCallError[] {
   const toolSchemaByName = new Map<string, unknown>();
+  const knownToolNames = new Set<string>();
   for (const tool of tools ?? []) {
     if (tool.type === 'function') {
+      knownToolNames.add(tool.function.name);
       toolSchemaByName.set(tool.function.name, tool.function.parameters);
     }
   }
@@ -109,6 +139,7 @@ function detectChatCompletionSseErrors(
   const errors: ToolCallError[] = [];
   for (const [, acc] of byIndex) {
     if (!acc.name) continue;
+    if (!checkKnownTool(knownToolNames, acc.id, acc.name, errors)) continue;
     const result = parseArgsString(acc.arguments, acc.id, acc.name, errors);
     if (result.ok) {
       validateAgainstSchema(
@@ -128,8 +159,10 @@ function detectResponsesSseErrors(
   tools: OpenAI.Responses.ResponseCreateParams['tools']
 ): ToolCallError[] {
   const toolSchemaByName = new Map<string, unknown>();
+  const knownToolNames = new Set<string>();
   for (const tool of tools ?? []) {
     if (tool.type === 'function') {
+      knownToolNames.add(tool.name);
       toolSchemaByName.set(tool.name, tool.parameters);
     }
   }
@@ -143,6 +176,7 @@ function detectResponsesSseErrors(
     const callId: string = event.item.call_id;
     const name: string = event.item.name;
     const argsStr: string = event.item.arguments;
+    if (!checkKnownTool(knownToolNames, callId, name, errors)) continue;
     const result = parseArgsString(argsStr, callId, name, errors);
     if (result.ok) {
       validateAgainstSchema(result.parsed, toolSchemaByName.get(name), callId, name, errors);
@@ -156,7 +190,9 @@ function detectMessagesSseErrors(
   tools: Anthropic.MessageCreateParams['tools']
 ): ToolCallError[] {
   const toolSchemaByName = new Map<string, unknown>();
+  const knownToolNames = new Set<string>();
   for (const tool of tools ?? []) {
+    knownToolNames.add(tool.name);
     // Anthropic.Tool has input_schema; server tools (BashTool, TextEditorTool, etc.) do not
     if ('input_schema' in tool) {
       toolSchemaByName.set(tool.name, tool.input_schema);
@@ -179,6 +215,7 @@ function detectMessagesSseErrors(
 
   const errors: ToolCallError[] = [];
   for (const [, acc] of byIndex) {
+    if (!checkKnownTool(knownToolNames, acc.id, acc.name, errors)) continue;
     const result = parseArgsString(acc.arguments, acc.id, acc.name, errors);
     if (result.ok) {
       // acc.arguments is accumulated JSON — validate against tool schema