Tool Call with `arguments: ""` fails due to JSON parsing error

[pReya]

Describe the bug

My problem is very similar to the problem described in #499, however I'm using vercel/ai instead of OpenRouter (though this should be irrelevant here, I think).

Tool calls should not fail when there is an empty string in arguments: "". While this might be a wrong format by the caller, the Agents SDK should still be robust enough to not crash.

The exact error I'm getting is:

error: SyntaxError: Unexpected end of JSON input
      at JSON.parse (<anonymous>)
      at runSingleTool (/Users/user1/backend/node_modules/@openai/agents-core/src/runImplementation.ts:1194:5)
      at Array.map (<anonymous>)
      at executeFunctionToolCalls (/Users/user1/node_modules/@openai/agents-core/src/runImplementation.ts:1335:25)
      at resolveTurnAfterModelResponse (/Users/user1/node_modules/@openai/agents-core/src/runImplementation.ts:711:7)
      at Runner.#runStreamLoop (/Users/user1/node_modules/@openai/agents-core/src/run.ts:1113:65)
      at process.processTicksAndRejections (node:internal/process/task_queues:105:5)

I've logged the Tool call object (toolRun.toolCall in executeFunctionToolCalls()) :

{
  "type": "function_call",
  "callId": "toolu_01XvwabcXWkJrR7iTECAJxwX",
  "name": "list_teams",
  "status": "completed",
  "arguments": ""
}

Debug information

• Agents SDK version: 0.3.2
• Runtime environment: Node.js v22.17.1

Repro steps

I'm not sure how to come up with a reproduction, since this relies on an external MCP server in my case.

Expected behavior

The empty string should be handled/parsed gracefully without resulting in a crash.

[seratch]

Which model do you use?

[pReya]

@seratch I'm using claude-4-sonnet-20250514 via aisdk(anthropic('claude-4-sonnet-20250514'))

Does this play a role here? The problematic call in runSingleTool seems to be model-independent, right?

[seratch]

at runSingleTool (/Users/user1/backend/node_modules/@openai/agents-core/src/runImplementation.ts:1194:5)

I don't think you're using the latest version because L1194 in the code is code comment: https://github.com/openai/openai-agents-js/blob/v0.3.2/packages/agents-core/src/runImplementation.ts#L1194

[pReya]

The line numbers are off, because I've added debug output myself to the code. I've double checked the installed version (it's 0.3.2). When I remove my debug output, the line numbers will match:

I've copied the whole error log (I've removed the runState object for brevity):

[Nest] 73657  - 11/19/2025, 11:41:24 AM   ERROR [PromptController] ToolCallError: Failed to run function tools: SyntaxError: Unexpected end of JSON input
    at executeFunctionToolCalls (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:1336:11)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async Promise.all (index 0)
    at async resolveTurnAfterModelResponse (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:710:5)
    at async Runner.#runStreamLoop (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/run.ts:1113:30) {
  state: RunState {
    [...]
  },
  error: SyntaxError: Unexpected end of JSON input
      at JSON.parse (<anonymous>)
      at runSingleTool (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:1191:27)
      at Array.map (<anonymous>)
      at executeFunctionToolCalls (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:1333:48)
      at resolveTurnAfterModelResponse (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:711:7)
      at Runner.#runStreamLoop (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/run.ts:1113:65)
      at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
}
node:events:496
      throw er; // Unhandled 'error' event
      ^

ToolCallError: Failed to run function tools: SyntaxError: Unexpected end of JSON input
    at executeFunctionToolCalls (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:1336:11)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async Promise.all (index 0)
    at async resolveTurnAfterModelResponse (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:710:5)
    at async Runner.#runStreamLoop (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/run.ts:1113:30)
Emitted 'error' event on Readable instance at:
    at emitErrorNT (node:internal/streams/destroy:170:8)
    at emitErrorCloseNT (node:internal/streams/destroy:129:3)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21) {
  state: RunState {
    [...]
  },
  error: SyntaxError: Unexpected end of JSON input
      at JSON.parse (<anonymous>)
      at runSingleTool (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:1191:27)
      at Array.map (<anonymous>)
      at executeFunctionToolCalls (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:1333:48)
      at resolveTurnAfterModelResponse (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/runImplementation.ts:711:7)
      at Runner.#runStreamLoop (/Users/user1/Code/project1-backend/node_modules/@openai/agents-core/src/run.ts:1113:65)
      at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
}

[pReya]

I can fix/avoid this error by adding a check for empty string in line 806 in dist/runImplementation.js to look like this:

Before:
if (toolRun.tool.parameters) {

After:
if (toolRun.tool.parameters && parsedArgs !== '') {