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

[ertembiyik]

Summary

Some models on OpenRouter called tools with empty object params using "" instead of {}, when headed to traces, it's clear that agent is calling tools with empty args:

{
  "callId": "toolu_vrtx_019cputrBMsRPi8nKmGGjS1y",
  "name": "LINEAR_LIST_LINEAR_PROJECTS",
  "type": "function_call",
  "arguments": "",
  "providerData": {
    ...
  },
  "status": "completed"
}

This results in error:

ToolCallError: Failed to run function tools: SyntaxError: Unexpected end of JSON input

Example

Here is a minimal reproducible example:

agents-bug.zip

import { Agent, run } from "@openai/agents";
import { aisdk } from "@openai/agents-extensions";
import { createOpenRouter } from "@openrouter/ai-sdk-provider";
import { Composio } from "@composio/core";
import { OpenAIAgentsProvider } from "@composio/openai-agents";

// Replace these placeholder values with your real credentials before running the example.
const OPENROUTER_API_KEY = "";
const COMPOSIO_API_KEY = "";
const COMPOSIO_USER_ID = "";

async function main() {
    if (
        [OPENROUTER_API_KEY, COMPOSIO_API_KEY, COMPOSIO_USER_ID].some((value) =>
            value === ""
        )
    ) {
        throw new Error("Update the API key placeholders before running this example.");
    }
    const composio = new Composio({
        apiKey: COMPOSIO_API_KEY,
        provider: new OpenAIAgentsProvider({ strict: true }),
    });
    const linearTool = await composio.tools.get(COMPOSIO_USER_ID, {
        toolkits: ["LINEAR"]
    });
    const openrouter = createOpenRouter({
        apiKey: OPENROUTER_API_KEY,
    });
    const model = aisdk(openrouter("anthropic/claude-sonnet-4"));
    const agent = new Agent({
        name: "Linear Projects Agent",
        instructions: "Use the Linear tool to list projects and summarize them for the user.",
        model,
        tools: linearTool,
    });
    console.log("Running agent with LINEAR_LIST_LINEAR_PROJECTS...");
    const result = await run(agent, "List all projects in the connected Linear workspace.");
    console.log("Final agent output:", result.finalOutput ?? "No final output.");
}

main().catch((error) => {
    console.error("Agent execution failed:", error);
});

1. Replace variable at the top with real values
2. Run install and dev scripts:

pnpm i
pnpm run dev

Changes

• Compare the tool params type from schema to the actual call and map "" to {} if needed

Tests

• New tests validate both tools and handoffs for mapping "" to {} where appropriate

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🦋 Changeset detected

Latest commit: 938a841

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@openai/agents-extensions	Minor

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[ertembiyik]

Related to vercel/ai#6687

[seratch]

Thanks for sending this, but I am unsure if this should be done on this SDK side.

[github-actions]

This PR is stale because it has been open for 10 days with no activity.

[walkerheathr24-rgb]

Thank you for all of the help! I wasn't able to get to it sooner due have a procedure. It is the 9th one this year so that I really appreciate all of the support on this!

[github-actions]

This PR is stale because it has been open for 10 days with no activity.

[seratch]

@ertembiyik I haven't checked this for a while, but doesn't the latest ai-sdk still handle this pattern in a good way? If yes, we may consider having this workaround on our side.

[ertembiyik]

@ertembiyik I haven't checked this for a while, but doesn't the latest ai-sdk still handle this pattern in a good way? If yes, we may consider having this workaround on our side.

hey! let me check it today with ai-sdk/provider version 3 and come back

[ertembiyik]

upd: i have tested the issue against ai sdk v6.0.0-beta.72 and @ai-sdk/provider v3.0.0-beta.8

the issue is still reproducible, i have simplified the example to not include composio, im now using a tool from @openai/agents with an empty object

important to mention that this issue seems to be reproducible on anthropic/claude-sonnet-4 model from openrouter, though on x-ai/grok-4-fast it seems to work just fine

here is the example i used:
agents-bug-ai-sdk-v6.zip

[ertembiyik]

but i believe you are right that this is not the place for such patch, it should be done in openrouter sdk or ai sdk itself i guess

did one more test, where i took pure ai sdk solution w/ openrouter without relying on agents sdk. it did fine for anthropic/claude-sonnet-4 in the exact same empty object case

here it is:
agents-bug-pure-ai-sdk.zip

with that said, seems like the agents sdk is the source of the issue