[Agents] Parallel tool execution fails

[mmalinov]

Hi,
I created an agent using gemini-2.5-flash connected to a streamable-http MCP server.
The agent fails to execute parallel tools when the LLM invokes them at once. Example prompt:
"Create 10 generic assets":

I think the issue is either related to race condition or incorrect parsing of the LLM response, invoking the tools, as the last requested tool combines the payloads of each before that:

I tried to find a fix/workaround by implementing tool chunking logic in @librechat/agents/dist/cjs/stream.cjs and @librechat/agents/dist/cjs/tools/handlers.cjs but so far without success.

Some additional logs of the agent:

messages:
  - lc: 1
    type: constructor
    id:
      - langchain_core
      - messages
      - AIMessageChunk
    kwargs:
      content:
        - type: text
          text: |
            Great! I have successfully retrieved your user profile. Your user ID is **8f65e6c1-f47f-11ef-8517-0242ac120011**. I will use this as the risk owner for the new assets.

            Now, I will proceed to create 10 generic assets. I will assign them names like "Generic Asset 1" to "Generic Asset 10", along with corresponding generic hostnames and IP addresses.
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                ip: 192.168.1.1
                name: Generic Asset 1
                hostname: generic-asset-1.com
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                name: Generic Asset 2
                hostname: generic-asset-2.com
                ip: 192.168.1.2
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                ip: 192.168.1.3
                name: Generic Asset 3
                hostname: generic-asset-3.com
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                ip: 192.168.1.4
                name: Generic Asset 4
                hostname: generic-asset-4.com
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                hostname: generic-asset-5.com
                name: Generic Asset 5
                ip: 192.168.1.5
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                ip: 192.168.1.6
                hostname: generic-asset-6.com
                name: Generic Asset 6
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                name: Generic Asset 7
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
                hostname: generic-asset-7.com
                ip: 192.168.1.7
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                name: Generic Asset 8
                hostname: generic-asset-8.com
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
                ip: 192.168.1.8
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                ip: 192.168.1.9
                hostname: generic-asset-9.com
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
                name: Generic Asset 9
        - functionCall:
            name: Create_Asset_mcp_k
            args:
              body:
                hostname: generic-asset-10.com
                risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
                ip: 192.168.1.10
                name: Generic Asset 10
      additional_kwargs:
        reasoning: |+
          **Begin Constructing Assets**

          I've successfully retrieved the user's profile and extracted the `risk_owner_id`. My next step is to initiate a loop that will call the `Create_Asset_mcp_k` tool ten times. I'll use generic values for `hostname`, `ip`, and `name` in each iteration to craft the assets, using the retrieved `risk_owner_id`.


          **Commencing Iterations for Assets**

          I'm now implementing the iterative process to create the ten generic assets. I've set up the loop and am ready to call the `Create_Asset_mcp_k` tool ten times, substituting the `risk_owner_id` ("8f65e6c1-f47f-11ef-8517-0 242ac120011") and generic values for hostname, IP, and name. Assets will be named "Generic Asset 1" through "Generic Asset 10", and the corresponding hostnames and IPs are ready to be used.


      response_metadata: {}
      tool_call_chunks:
        - name: Create_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_k
          args: '{"body":{"ip":"192.168.1.1","name":"Generic Asset 1","hostname":"generic-asset-1.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"name":"Generic Asset 2","hostname":"generic-asset-2.com","ip":"192.168.1.2","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"ip":"192.168.1.3","name":"Generic Asset 3","hostname":"generic-asset-3.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"ip":"192.168.1.4","name":"Generic Asset 4","hostname":"generic-asset-4.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"hostname":"generic-asset-5.com","name":"Generic Asset 5","ip":"192.168.1.5","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"ip":"192.168.1.6","hostname":"generic-asset-6.com","name":"Generic Asset 6","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"name":"Generic Asset 7","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-7.com","ip":"192.168.1.7"}}{"body":{"name":"Generic Asset 8","hostname":"generic-asset-8.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","ip":"192.168.1.8"}}{"body":{"ip":"192.168.1.9","hostname":"generic-asset-9.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","name":"Generic Asset 9"}}{"body":{"hostname":"generic-asset-10.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","ip":"192.168.1.10","name":"Generic Asset 10"}}'
          index: 5
          type: tool_call_chunk
          id: a4870537-ce03-4604-87f4-dbab2b763f338f18e8c8-1ff6-4864-acdb-b105a41d467d0f286960-cbcb-43b3-b49c-3d75ed47260f7e5d817d-3da6-432b-8769-b7722ae91d999c9f44db-4ce1-4bea-8381-2b765199ca40ea697f52-f2d4-4f0d-8c0e-c8ce32d03002927cf27c-0e52-4396-99de-2ba044388d8e332c75de-3c6e-4b09-87ec-9f329ce3cf42547a35f8-d340-496b-8b95-a65660fd5843fd68e156-eac2-45d6-82c9-b5a181e1baa1
      id: run-59f16232-4d84-42ea-aa0c-aa70af76584f
      usage_metadata:
        input_tokens: 12731
        output_tokens: 1292
        total_tokens: 14023
        model: gemini-2.5-flash
      tool_calls: []
      invalid_tool_calls:
        - name: Create_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_k
          args: '{"body":{"ip":"192.168.1.1","name":"Generic Asset 1","hostname":"generic-asset-1.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"name":"Generic Asset 2","hostname":"generic-asset-2.com","ip":"192.168.1.2","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"ip":"192.168.1.3","name":"Generic Asset 3","hostname":"generic-asset-3.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"ip":"192.168.1.4","name":"Generic Asset 4","hostname":"generic-asset-4.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"hostname":"generic-asset-5.com","name":"Generic Asset 5","ip":"192.168.1.5","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"ip":"192.168.1.6","hostname":"generic-asset-6.com","name":"Generic Asset 6","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}{"body":{"name":"Generic Asset 7","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-7.com","ip":"192.168.1.7"}}{"body":{"name":"Generic Asset 8","hostname":"generic-asset-8.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","ip":"192.168.1.8"}}{"body":{"ip":"192.168.1.9","hostname":"generic-asset-9.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","name":"Generic Asset 9"}}{"body":{"hostname":"generic-asset-10.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","ip":"192.168.1.10","name":"Generic Asset 10"}}'
          id: a4870537-ce03-4604-87f4-dbab2b763f338f18e8c8-1ff6-4864-acdb-b105a41d467d0f286960-cbcb-43b3-b49c-3d75ed47260f7e5d817d-3da6-432b-8769-b7722ae91d999c9f44db-4ce1-4bea-8381-2b765199ca40ea697f52-f2d4-4f0d-8c0e-c8ce32d03002927cf27c-0e52-4396-99de-2ba044388d8e332c75de-3c6e-4b09-87ec-9f329ce3cf42547a35f8-d340-496b-8b95-a65660fd5843fd68e156-eac2-45d6-82c9-b5a181e1baa1
          error: Malformed args.
          type: invalid_tool_call
  

If the LLM invokes the tools one after another(waits for successful completion of each) there is no such case.

Any help is appreciated!

[danny-avila]

It seems to be only an issue for Gemini, and I confirmed it with raw API calls, without too much LC-specific logic in the mix.

You can even see it in your logs:

invalid_tool_calls:
        - name: Create_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_kCreate_Asset_mcp_k
          args: '{"body":{"ip":"192.168.1.1","name":"Generic Asset 1",...}}{"body":{"name":"Generic Asset 2",...}}{"body":{"ip":"192.168.1.3",...}}{"body":{"ip":"192.168.1.4",...}}{"body":{"hostname":"generic-asset-5.com",...}}{"body":{"ip":"192.168.1.6",...}}{"body":{"name":"Generic Asset 7",...}}{"body":{"name":"Generic Asset 8",...}}{"body":{"ip":"192.168.1.9",...}}{"body":{"hostname":"generic-asset-10.com",...}}'
          error: Malformed args.
          type: invalid_tool_call

The LLM/Google is essentially combining all the tool call fields into each "parallel" call, which creates the malformed args error.

[danny-avila]

I will look into it and see if I can resolve this, since Gemini forms these outputs uniquely

[mmalinov]

Hi Dany,

Thanks for the reply!

I have a small update on the topic:
We have made a couple of changes to @librechat/agents/dist/cjs/llm/google/index.cjs and it seems that there might be a workaround. The change is in the "*_streamResponseChunks" function, basically adding/replacing some part of the existing logic with this one:

const parts = response.candidates?.[0]?.content?.parts ?? [];
        for (const part of parts) {
            let chunk;
            if (part.text) {
                chunk = new outputs.ChatGenerationChunk({
                    text: part.text,
                    message: new messages.AIMessageChunk({ content: part.text }),
                });
            } else if (part.functionCall) {
                const { functionCall } = part;
                const argsString = JSON.stringify(functionCall.args ?? {});
                chunk = new outputs.ChatGenerationChunk({
                    text: '', 
                    message: new messages.AIMessageChunk({
                        content: '',
                        additional_kwargs: {
                            tool_calls: [], 
                        },
                        tool_call_chunks: [{
                            name: functionCall.name,
                            args: argsString,
                            id: `call_${uuid.v4()}`,
                            type: "tool_call_chunk",
                        }, ],
                    }),
                });
            }

            if (chunk) {
                yield chunk;
                await runManager?.handleLLMNewToken(chunk.text || "", undefined, undefined, undefined, undefined, { chunk });
            }
        }

It iterates over the multiple parts of the response and splits them into chunks. Now the parallel tool calling is working as expected:

Some logs from the agent highlighting that there aren't invalid tool calls this time:

messages:
  - lc: 1
    type: constructor
    id:
      - langchain_core
      - messages
      - AIMessageChunk
    kwargs:
      content: |
        Now that I have your user ID, I will proceed to create 10 generic assets. Each asset will have a unique name (e.g., "Generic Asset 1", "Generic Asset 2", etc.) and a corresponding hostname (e.g., "generic-asset-1.com", "generic-asset-2.com", etc.). Your user ID will be assigned as the risk owner for all these assets.

        This process will help you quickly populate your asset inventory with placeholder entries that you can later update with more specific details.
      additional_kwargs:
        tool_calls: []
      response_metadata: {}
      tool_call_chunks:
        - name: Create_Asset_mcp_k
          args: '{"body":{"risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-1.com","name":"Generic Asset 1"}}'
          id: call_760081e6-7cd1-4754-bb3c-e8f55f30c8e5
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"hostname":"generic-asset-2.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","name":"Generic Asset 2"}}'
          id: call_ed34907a-88d2-4cb1-bbc1-6973d65a607a
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"hostname":"generic-asset-3.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","name":"Generic Asset 3"}}'
          id: call_adda04e3-9306-4072-8cb9-a721bdc7f271
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"hostname":"generic-asset-4.com","name":"Generic Asset 4","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011"}}'
          id: call_c945d323-61b7-4647-a150-3a53d4990eee
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"hostname":"generic-asset-5.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","name":"Generic Asset 5"}}'
          id: call_ef7563ea-bb7a-4441-ae2f-bdabc1b77d85
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"hostname":"generic-asset-6.com","risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","name":"Generic Asset 6"}}'
          id: call_f5cb1b38-6679-4cdf-ad2a-9a663a61dcfa
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-7.com","name":"Generic Asset 7"}}'
          id: call_ec67bb03-a7c3-4c43-bb6f-38778b70090b
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-8.com","name":"Generic Asset 8"}}'
          id: call_5c9747fa-2306-4a5e-b998-3bb3ef7136d3
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-9.com","name":"Generic Asset 9"}}'
          id: call_fdee4ed2-1ed9-41ce-adcd-c5838860ed7d
          type: tool_call_chunk
        - name: Create_Asset_mcp_k
          args: '{"body":{"risk_owner_id":"8f65e6c1-f47f-11ef-8517-0242ac120011","hostname":"generic-asset-10.com","name":"Generic Asset 10"}}'
          id: call_5ef9ee6c-92b4-411b-8b76-244ea66a9592
          type: tool_call_chunk
      id: run-4a50da32-c906-4ca6-b6d3-c066736724b7
      usage_metadata:
        input_tokens: 12728
        output_tokens: 935
        total_tokens: 13663
        model: gemini-2.5-flash
      tool_calls:
        - name: Create_Asset_mcp_k
          args:
            body:
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              hostname: generic-asset-1.com
              name: Generic Asset 1
          id: call_760081e6-7cd1-4754-bb3c-e8f55f30c8e5
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              hostname: generic-asset-2.com
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              name: Generic Asset 2
          id: call_ed34907a-88d2-4cb1-bbc1-6973d65a607a
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              hostname: generic-asset-3.com
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              name: Generic Asset 3
          id: call_adda04e3-9306-4072-8cb9-a721bdc7f271
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              hostname: generic-asset-4.com
              name: Generic Asset 4
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
          id: call_c945d323-61b7-4647-a150-3a53d4990eee
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              hostname: generic-asset-5.com
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              name: Generic Asset 5
          id: call_ef7563ea-bb7a-4441-ae2f-bdabc1b77d85
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              hostname: generic-asset-6.com
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              name: Generic Asset 6
          id: call_f5cb1b38-6679-4cdf-ad2a-9a663a61dcfa
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              hostname: generic-asset-7.com
              name: Generic Asset 7
          id: call_ec67bb03-a7c3-4c43-bb6f-38778b70090b
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              hostname: generic-asset-8.com
              name: Generic Asset 8
          id: call_5c9747fa-2306-4a5e-b998-3bb3ef7136d3
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              hostname: generic-asset-9.com
              name: Generic Asset 9
          id: call_fdee4ed2-1ed9-41ce-adcd-c5838860ed7d
          type: tool_call
        - name: Create_Asset_mcp_k
          args:
            body:
              risk_owner_id: 8f65e6c1-f47f-11ef-8517-0242ac120011
              hostname: generic-asset-10.com
              name: Generic Asset 10
          id: call_5ef9ee6c-92b4-411b-8b76-244ea66a9592
          type: tool_call
      invalid_tool_calls: []

However with this logic, the thought of the model are displayed in the response body, not as a 'hidden' element/button. For the example above I have turned off the thinking as it generates a lot of noise.

I don't know how robust/feasible this solution is, as I am not sure how it relates to the other LC logic.
I am just sharing some feedback, that I hope, is useful for resolving this properly.

[danny-avila]

this change is enough to fix it: danny-avila/agents@65b2f36

#8458

[danny-avila]

[mmalinov]

Hi Dany,

Thanks for the support, everything works fine!