ChatCerebras fails to call tools when messages.content === "" #8643
Description
Checked other resources
- This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/).
- I added a very descriptive title to this issue.
- I searched the LangChain.js documentation with the integrated search.
- I used the GitHub search to find a similar question and didn't find it.
- I am sure that this is a bug in LangChain.js rather than my code.
- The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
NOTE: I have a fix: hideya@01577b5
I wanted to file a PR, but I currently don't have enough time to fully test the fix... (sorry...)
Example Code
import { ChatCerebras } from '@langchain/cerebras';
import { createReactAgent } from "@langchain/langgraph/prebuilt";
import { HumanMessage } from "@langchain/core/messages";
import { tool } from '@langchain/core/tools';
const magicTool = tool(
({ input }) => {
return '42';
},
{
name: 'magic_function',
description: 'Applies a magic function to an input.',
},
);
const llm = new ChatCerebras({
model: 'gpt-oss-120b',
});
const agent = createReactAgent({
llm,
tools: [magicTool]
});
const query = 'Can you apply the magic function to 123?';
const messages = { messages: [new HumanMessage(query)] };
const result = await agent.invoke(messages);
const response = result.messages[result.messages.length - 1].content;
console.log(response);Error Message and Stack Trace (if applicable)
file:///.../langchain-cerebras-bug/node_modules/@cerebras/cerebras_cloud_sdk/error.mjs:36
return new BadRequestError(status, error, message, headers);
^
BadRequestError: 400 Messages with role 'tool' must be a response to a preceeding message with 'tool_calls'
at APIError.generate (file:///.../langchain-cerebras-bug/node_modules/@cerebras/cerebras_cloud_sdk/error.mjs:36:20)
at Cerebras.makeStatusError (file:///.../langchain-cerebras-bug/node_modules/@cerebras/cerebras_cloud_sdk/core.mjs:286:25)
at Cerebras.makeRequest (file:///.../langchain-cerebras-bug/node_modules/@cerebras/cerebras_cloud_sdk/core.mjs:332:30)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async file:///.../langchain-cerebras-bug/node_modules/@langchain/cerebras/dist/chat_models.js:504:25
at async RetryOperation._fn (/...langchain-cerebras-bug/node_modules/p-retry/index.js:50:12) {
status: 400,
headers: {
'alt-svc': 'h3=":443"; ma=86400',
'cf-cache-status': 'DYNAMIC',
'cf-ray': '96ba1e55892305b2-KIX',
connection: 'keep-alive',
'content-length': '176',
'content-type': 'application/json',
date: 'Thu, 07 Aug 2025 22:12:58 GMT',
'referrer-policy': 'strict-origin-when-cross-origin',
server: 'cloudflare',
'set-cookie': '...',
'strict-transport-security': 'max-age=3600; includeSubDomains',
'x-content-type-options': 'nosniff'
},
error: {
message: "Messages with role 'tool' must be a response to a preceeding message with 'tool_calls'",
type: 'invalid_request_error',
param: 'messages',
code: 'wrong_api_format'
},
attemptNumber: 1,
retriesLeft: 6,
pregelTaskId: '2fe113f1-efdf-56f3-b0b6-045ca3c5ae83'
}
Node.js v20.18.1
Description
When I run the above example code, I get the above error.
I looked into the cause and found an issue in
langchainjs/libs/langchain-cerebras/src/utils.ts
Lines 53 to 60 in feff0c9
The issue is that messages.content is set to "" when calling tools, thus it fails to perform tool calling.
I guess messages.content is expected to be null, but the reality is that the above test code passes "".
This diffs should fix the error: hideya@01577b5
I applied equivalent changes to node_modules/@langchain/cerebras/dist/utils.js and confirmed it fixes the error.
System Info
% yarn info @langchain/cerebras
...
name: '@langchain/cerebras',
'dist-tags': {
latest: '0.0.2'
},
...
% sw_vers
ProductName: macOS
ProductVersion: 15.6
BuildVersion: 24G84
% node -v
v20.18.1