fix: non-OpenAI models w/ OpenRouter send an empty string when calling tools (#499)

Co-authored-by: Kazuhiro Sera <[email protected]>

Author: ertembiyik

.changeset/quick-frogs-lie.md

@@ -0,0 +1,5 @@
+---
+'@openai/agents-extensions': patch
+---
+
+Fix open ai compatible models misuse '' in tools arguments call when an empty object is the valid option

packages/agents-extensions/src/aiSdk.ts

@@ -357,6 +357,36 @@ function convertLegacyToolOutputContent(
   );
 }
 
+function schemaAcceptsObject(schema: JSONSchema7 | undefined): boolean {
+  if (!schema) {
+    return false;
+  }
+  const schemaType = schema.type;
+  if (Array.isArray(schemaType)) {
+    if (schemaType.includes('object')) {
+      return true;
+    }
+  } else if (schemaType === 'object') {
+    return true;
+  }
+  return Boolean(schema.properties || schema.additionalProperties);
+}
+
+function expectsObjectArguments(
+  tool: SerializedTool | SerializedHandoff | undefined,
+): boolean {
+  if (!tool) {
+    return false;
+  }
+  if ('toolName' in tool) {
+    return schemaAcceptsObject(tool.inputJsonSchema as JSONSchema7 | undefined);
+  }
+  if (tool.type === 'function') {
+    return schemaAcceptsObject(tool.parameters as JSONSchema7 | undefined);
+  }
+  return false;
+}
+
 /**
  * Maps the protocol-level structured outputs into the Language Model V2 result primitives.
  * The AI SDK expects either plain text or content parts (text + media), so we merge multiple
@@ -630,15 +660,41 @@ export class AiSdkModel implements Model {
           (c: any) => c && c.type === 'tool-call',
         );
         const hasToolCalls = toolCalls.length > 0;
+
+        const toolsNameToToolMap = new Map<
+          string,
+          SerializedTool | SerializedHandoff
+        >(request.tools.map((tool) => [tool.name, tool] as const));
+
+        for (const handoff of request.handoffs) {
+          toolsNameToToolMap.set(handoff.toolName, handoff);
+        }
         for (const toolCall of toolCalls) {
+          const requestedTool =
+            typeof toolCall.toolName === 'string'
+              ? toolsNameToToolMap.get(toolCall.toolName)
+              : undefined;
+
+          if (!requestedTool && toolCall.toolName) {
+            this.#logger.warn(
+              `Received tool call for unknown tool '${toolCall.toolName}'.`,
+            );
+          }
+
+          let toolCallArguments: string;
+          if (typeof toolCall.input === 'string') {
+            toolCallArguments =
+              toolCall.input === '' && expectsObjectArguments(requestedTool)
+                ? JSON.stringify({})
+                : toolCall.input;
+          } else {
+            toolCallArguments = JSON.stringify(toolCall.input ?? {});
+          }
           output.push({
             type: 'function_call',
             callId: toolCall.toolCallId,
             name: toolCall.toolName,
-            arguments:
-              typeof toolCall.input === 'string'
-                ? toolCall.input
-                : JSON.stringify(toolCall.input ?? {}),
+            arguments: toolCallArguments,
             status: 'completed',
             providerData: hasToolCalls ? result.providerMetadata : undefined,
           });

packages/agents-extensions/test/aiSdk.test.ts

@@ -462,6 +462,110 @@ describe('AiSdkModel.getResponse', () => {
     ]);
   });
 
+  test('normalizes empty string tool input for object schemas', async () => {
+    const model = new AiSdkModel(
+      stubModel({
+        async doGenerate() {
+          return {
+            content: [
+              {
+                type: 'tool-call',
+                toolCallId: 'call-1',
+                toolName: 'objectTool',
+                input: '',
+              },
+            ],
+            usage: { inputTokens: 1, outputTokens: 1, totalTokens: 2 },
+            providerMetadata: { meta: true },
+            response: { id: 'id' },
+            finishReason: 'tool-calls',
+            warnings: [],
+          } as any;
+        },
+      }),
+    );
+
+    const res = await withTrace('t', () =>
+      model.getResponse({
+        input: 'hi',
+        tools: [
+          {
+            type: 'function',
+            name: 'objectTool',
+            description: 'accepts object',
+            parameters: {
+              type: 'object',
+              properties: {},
+              additionalProperties: false,
+            },
+          } as any,
+        ],
+        handoffs: [],
+        modelSettings: {},
+        outputType: 'text',
+        tracing: false,
+      } as any),
+    );
+
+    expect(res.output).toHaveLength(1);
+    expect(res.output[0]).toMatchObject({
+      type: 'function_call',
+      arguments: '{}',
+    });
+  });
+
+  test('normalizes empty string tool input for handoff schemas', async () => {
+    const model = new AiSdkModel(
+      stubModel({
+        async doGenerate() {
+          return {
+            content: [
+              {
+                type: 'tool-call',
+                toolCallId: 'handoff-call',
+                toolName: 'handoffTool',
+                input: '',
+              },
+            ],
+            usage: { inputTokens: 1, outputTokens: 1, totalTokens: 2 },
+            providerMetadata: { meta: true },
+            response: { id: 'id' },
+            finishReason: 'tool-calls',
+            warnings: [],
+          } as any;
+        },
+      }),
+    );
+
+    const res = await withTrace('t', () =>
+      model.getResponse({
+        input: 'hi',
+        tools: [],
+        handoffs: [
+          {
+            toolName: 'handoffTool',
+            toolDescription: 'handoff accepts object',
+            inputJsonSchema: {
+              type: 'object',
+              properties: {},
+              additionalProperties: false,
+            },
+            strictJsonSchema: true,
+          } as any,
+        ],
+        modelSettings: {},
+        outputType: 'text',
+        tracing: false,
+      } as any),
+    );
+
+    expect(res.output).toHaveLength(1);
+    expect(res.output[0]).toMatchObject({
+      type: 'function_call',
+      arguments: '{}',
+    });
+  });
+
   test('forwards toolChoice to AI SDK (generate)', async () => {
     const seen: any[] = [];
     const model = new AiSdkModel(