Mastra•3w ago

Tool output not being passed back to agent

Hey everyone, I’m running into a consistent issue with Mastra (latest stable version 0.24.1) where a tool’s output isn’t being passed back to the agent during execution. What’s Happening: - The agent successfully calls the tool.
- The tool executes normally and produces the correct output.
- But the agent never receives the tool result—the process simply ends quietly with no error.
- No follow-up actions, no continuation, no reasoning loop—just a silent stop after the tool finishes. What I’ve Checked - Tool schema & return types are correct
- Agent is properly configured with the tool
- Clear instructions for returning text output
- Logging shows the tool’s return payload is generated
- Happens across multiple tools
- Using latest Mastra version
- Setup: Conversation (RAG) Agent + OpenRouter + AI SDK 5 + useChat hook + fastify server What I Expected The agent should consume the tool result and continue its thought/action chain, but the callback never triggers. --- Code Example screenshot attached Attached langufse screenshot PS: it was happening on previous version of Mastra as well, but I updated it to see if anything changes.

3 Replies

Mastra Triager•3w ago

📝 Created GitHub issue: https://github.com/mastra-ai/mastra/issues/10327 🔍 If you're experiencing an error, please provide a minimal reproducible example to help us resolve it quickly. 🙏 Thank you @expiredMedicine for helping us improve Mastra! 📝 Created GitHub issue: https://github.com/mastra-ai/mastra/issues/10328 🔍 If you're experiencing an error, please provide a minimal reproducible example to help us resolve it quickly. 🙏 Thank you @expiredMedicine for helping us improve Mastra! 📝 Created GitHub issue: https://github.com/mastra-ai/mastra/issues/10329 🔍 If you're experiencing an error, please provide a minimal reproducible example to help us resolve it quickly. 🙏 Thank you @expiredMedicine for helping us improve Mastra!

_roamin_•3w ago

Hi @expiredMedicine ! Could you try updating your API endpoint code to use this pattern instead, we've made a lot of changes/fixes to our stream transformer (remove the format: 'aisdk' and use toAISdkFormat instead:

import { createUIMessageStream, createUIMessageStreamResponse } from "ai";
import { toAISdkFormat } from "@mastra/ai-sdk";

// ...
const stream = await myAgent.stream(...);

return createUIMessageStreamResponse({
  stream: toAISdkFormat(stream, { from: "agent" }),
});

import { createUIMessageStream, createUIMessageStreamResponse } from "ai";
import { toAISdkFormat } from "@mastra/ai-sdk";

// ...
const stream = await myAgent.stream(...);

return createUIMessageStreamResponse({
  stream: toAISdkFormat(stream, { from: "agent" }),
});

Also, is the tool-result generated via human-in-the-loop, or is it a tool that doesn't require human interaction? Thanks! 🙏

Ward•6d ago

Try using our new server agnostic handlers https://unpkg.com/@mastra/ai-sdk@1.0.0-beta.5/README.md

import { handleChatStream } from '@mastra/ai-sdk';
import { createUIMessageStreamResponse } from 'ai';
import { mastra } from '@/src/mastra';

export async function POST(req: Request) {
  const params = await req.json();
  const stream = await handleChatStream({
    mastra,
    agentId: 'weatherAgent',
    params,
  });
  return createUIMessageStreamResponse({ stream });
}

import { handleChatStream } from '@mastra/ai-sdk';
import { createUIMessageStreamResponse } from 'ai';
import { mastra } from '@/src/mastra';

export async function POST(req: Request) {
  const params = await req.json();
  const stream = await handleChatStream({
    mastra,
    agentId: 'weatherAgent',
    params,
  });
  return createUIMessageStreamResponse({ stream });
}

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Tool output not being passed back to agent

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