fix: distinguish custom Anthropic web search tools

Author: jan-kubica

.changeset/tidy-searches-coexist.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/ai-anthropic': patch
+---
+
+Keep ordinary function tools named `web_search` distinct from Anthropic's native web-search tool by checking the provider metadata before conversion.

packages/ai-anthropic/src/tools/tool-converter.ts

@@ -9,6 +9,20 @@ import { convertWebSearchToolToAdapterFormat } from './web-search-tool'
 import type { AnthropicTool } from './index'
 import type { Tool } from '@tanstack/ai'
 
+function isAnthropicWebSearchTool(tool: Tool): boolean {
+  const metadata = tool.metadata
+  if (!metadata) {
+    return false
+  }
+
+  return (
+    'type' in metadata &&
+    metadata.type === 'web_search_20250305' &&
+    'name' in metadata &&
+    metadata.name === 'web_search'
+  )
+}
+
 /**
  * Converts standard Tool format to Anthropic-specific tool format
  *
@@ -53,7 +67,9 @@ export function convertToolsToProviderFormat<TTool extends Tool>(
       case 'web_fetch':
         return convertWebFetchToolToAdapterFormat(tool)
       case 'web_search':
-        return convertWebSearchToolToAdapterFormat(tool)
+        return isAnthropicWebSearchTool(tool)
+          ? convertWebSearchToolToAdapterFormat(tool)
+          : convertCustomToolToAdapterFormat(tool)
       default:
         return convertCustomToolToAdapterFormat(tool)
     }

packages/ai-anthropic/tests/provider-tools-smoke.test.ts

@@ -115,4 +115,28 @@ describe('convertToolsToProviderFormat — end-to-end shape', () => {
     expect(names).toContain('code_execution')
     expect(names).toContain('bash')
   })
+
+  it('keeps an ordinary function named web_search as a custom tool', () => {
+    const [converted] = convertToolsToProviderFormat([
+      {
+        name: 'web_search',
+        description: 'Search an application index',
+        inputSchema: {
+          type: 'object',
+          properties: { query: { type: 'string' } },
+          required: ['query'],
+        },
+      } satisfies Tool,
+    ])
+
+    expect(converted).toMatchObject({
+      name: 'web_search',
+      type: 'custom',
+      description: 'Search an application index',
+      input_schema: {
+        properties: { query: { type: 'string' } },
+        required: ['query'],
+      },
+    })
+  })
 })

testing/e2e/src/routes/api.anthropic-skills-wire.ts

@@ -1,10 +1,21 @@
 import { createFileRoute } from '@tanstack/react-router'
 import { chat, createChatOptions } from '@tanstack/ai'
+import type { Tool } from '@tanstack/ai'
 import { createAnthropicChat } from '@tanstack/ai-anthropic'
 import { codeExecutionTool } from '@tanstack/ai-anthropic/tools'
 
 const DUMMY_KEY = 'sk-ant-e2e-test-dummy-key'
 
+const customWebSearchTool = {
+  name: 'web_search',
+  description: 'Search an application index',
+  inputSchema: {
+    type: 'object',
+    properties: { query: { type: 'string' } },
+    required: ['query'],
+  },
+} satisfies Tool
+
 /**
  * Drives the Anthropic chat adapter with a `codeExecutionTool` carrying a
  * hosted skill. A custom `fetch` implementation intercepts the outgoing
@@ -138,6 +149,7 @@ export const Route = createFileRoute('/api/anthropic-skills-wire')({
                   ],
                 },
               ),
+              customWebSearchTool,
             ],
           })) {
             // Drain the stream.

testing/e2e/tests/anthropic-skills-wire.spec.ts

@@ -76,4 +76,37 @@ test.describe('anthropic — code_execution skills wire format', () => {
       version: 'latest',
     })
   })
+
+  test('an ordinary function named web_search stays a custom tool', async ({
+    request,
+  }) => {
+    const res = await request.post('/api/anthropic-skills-wire')
+    expect(res.ok()).toBe(true)
+    const { ok, error, capturedRequest } = (await res.json()) as {
+      ok: boolean
+      error?: string
+      capturedRequest: {
+        body: Record<string, unknown> | null
+      } | null
+    }
+
+    if (!ok) {
+      throw new Error(`Route failed: ${error}`)
+    }
+
+    const tools = capturedRequest?.body?.['tools'] as
+      | Array<Record<string, unknown>>
+      | undefined
+    const customTool = tools?.find((tool) => tool['name'] === 'web_search')
+
+    expect(customTool).toMatchObject({
+      name: 'web_search',
+      type: 'custom',
+      description: 'Search an application index',
+      input_schema: {
+        properties: { query: { type: 'string' } },
+        required: ['query'],
+      },
+    })
+  })
 })