fix(agents-core): handle invalid JSON in tool call arguments gracefully #887

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Merged

seratch merged 8 commits into openai:main from OlegHQ:fix/issue-723-invalid-json-handling

Jan 20, 2026

.changeset/fix-invalid-json-handling.md

-Original file line number
+Diff line change
@@ -0,0 +1,5 @@
+    ---
+    '@openai/agents-core': patch
+    ---
+    fix: #723 handle invalid JSON in tool call arguments gracefully to prevent agent crashes

packages/agents-core/src/runner/toolExecution.ts

-Original file line number
+Diff line change
@@ Expand Up / @@ -56,6 +56,10 @@ type FunctionToolCallDeps<TContext = UnknownContext> = { @@
     const TOOL_APPROVAL_REJECTION_MESSAGE = 'Tool execution was not approved.';
+    type ParseToolArgumentsResult =
+      | { success: true; args: any }
+      | { success: false; error: Error };
     /**
      * @internal
      * Normalizes tool outputs once so downstream code works with fully structured protocol items.
@@ Expand Down Expand Up @@
       try {
         const results = await Promise.all(
           toolRuns.map(async (toolRun) => {
-            const parsedArgs = parseToolArguments(toolRun);
+            const parseResult = parseToolArguments(toolRun);
+            // Handle parse errors gracefully instead of crashing
+            if (!parseResult.success) {
+              return buildParseErrorResult(deps, toolRun, parseResult.error);
+            }
             const approvalOutcome = await handleFunctionApproval(
               deps,
               toolRun,
-              parsedArgs,
+              parseResult.args,
             );
             if (approvalOutcome !== 'approved') {
               return approvalOutcome;
@@ Expand All @@
       }
     }
-    function parseToolArguments<TContext>(toolRun: ToolRunFunction<TContext>) {
-      let parsedArgs: any = toolRun.toolCall.arguments;
-      if (toolRun.tool.parameters) {
-        if (isZodObject(toolRun.tool.parameters)) {
-          parsedArgs = toolRun.tool.parameters.parse(parsedArgs);
-        } else {
-          parsedArgs = JSON.parse(parsedArgs);
+    function parseToolArguments<TContext>(
+      toolRun: ToolRunFunction<TContext>,
+    ): ParseToolArgumentsResult {
+      try {
+        let parsedArgs: any = toolRun.toolCall.arguments;
+        if (toolRun.tool.parameters) {
+          if (isZodObject(toolRun.tool.parameters)) {
+            parsedArgs = toolRun.tool.parameters.parse(parsedArgs);
+          } else {
+            parsedArgs = JSON.parse(parsedArgs);
+          }
         }
+        return { success: true, args: parsedArgs };
+      } catch (error) {
+        logger.debug(
+          `Failed to parse tool arguments for ${toolRun.tool.name}: ${error}`,
+        );
+        return { success: false, error: error as Error };
       }
-      return parsedArgs;
     }
     function buildApprovalRequestResult<TContext>(
@@ Expand All / @@ -154,6 +173,24 @@ function buildApprovalRequestResult<TContext>( @@
       };
     }
+    function buildParseErrorResult<TContext>(
+      deps: FunctionToolCallDeps<TContext>,
+      toolRun: ToolRunFunction<TContext>,
+      error: Error,
+    ): FunctionToolResult<TContext> {
+      const errorMessage = `An error occurred while parsing tool arguments. Please try again with valid JSON. Error: ${error.message}`;
+      return {
+        type: 'function_output',
+        tool: toolRun.tool,
+        output: errorMessage,
+        runItem: new RunToolCallOutputItem(
+          getToolCallOutputItem(toolRun.toolCall, errorMessage),
+          deps.agent,
+          errorMessage,
+        ),
+      };
+    }
     async function buildApprovalRejectionResult<TContext>(
       deps: FunctionToolCallDeps<TContext>,
       toolRun: ToolRunFunction<TContext>,
@@ Expand Down @@

packages/agents-core/test/runner/toolExecution.test.ts

-Original file line number
+Diff line change
@@ Expand Up / @@ -1284,6 +1284,46 @@ describe('executeShellActions', () => { @@
           expect(firstResult.agentRunResult).toBe(nestedRunResult);
           expect(firstResult.interruptions).toEqual([approval]);
         });
+        it('handles invalid JSON in tool call arguments gracefully instead of crashing', async () => {
+          // Reproduces issue #723: SyntaxError stops agent when LLM generates invalid JSON
+          const t = tool({
+            name: 'checkTagActivity',
+            description: 'Check tag activity',
+            parameters: z.object({
+              tagIds: z.array(z.string()),
+              since: z.string(),
+            }),
+            execute: vi.fn(async () => 'success'),
+          }) as unknown as FunctionTool;
+          const invalidToolCall = {
+            ...toolCall,
+            name: 'checkTagActivity',
+            arguments:
+              '{"{"tagIds":["65aafb7e-4293-4376-baf6-1f9d197e960a"],"since":"2025-09-04T13:26:13.991Z"}',
+          };
+          const res = await withTrace('test', () =>
+            executeFunctionToolCalls(
+              state._currentAgent,
+              [{ toolCall: invalidToolCall, tool: t }],
+              runner,
+              state,
+            ),
+          );
+          expect(res).toHaveLength(1);
+          const firstResult = res[0];
+          expect(firstResult.type).toBe('function_output');
+          if (firstResult.type === 'function_output') {
+            expect(String(firstResult.output)).toContain(
+              'An error occurred while parsing tool arguments',
+            );
+            expect(String(firstResult.output)).toContain('valid JSON');
+          }
+        });
       });
       describe('executeComputerActions', () => {
@@ Expand Down @@

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