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).

Example Code

    console.log(new AIMessage({
      content: "Here is the result.",
      tool_calls: [
        {
          name: "someTool",
          args: { stringArg: "someFile", objectArg: { key: "someValue" } }
        }
      ]
    }).toFormattedString());

// ================================== Ai Message ==================================
// Tool Calls:
//   someTool (undefined)
//  Call ID: undefined
//   Args:
//     stringArg: someFile
//     objectArg: [object Object]

// Here is the result.

Error Message and Stack Trace (if applicable)

No response

Description

When I format messages with toFormattedString() I would expect to see all arguments formatted in a readable way. Instead, only primitive values are formatted and objects are displayed as [object Object].

System Info

npm info langchain

[email protected] | MIT | deps: 5 | versions: 348
Typescript bindings for langchain
https://github.com/langchain-ai/langchainjs/tree/main/libs/langchain/

keywords: llm, ai, gpt3, chain, prompt, prompt engineering, chatgpt, machine learning, ml, openai, embeddings, vectorstores

dist
.tarball: https://registry.npmjs.org/langchain/-/langchain-1.1.1.tgz
.shasum: 6f0392a9971f16d69264d4e8ff4a1085b1c96136
.integrity: sha512-z7cOFhLOzbu/lRlIE8GZ5rlfi7obvvHThhMdts1KsUBusJmWLmh1Yik28MHYzJRXclUbqs4u/9D2yNmr36wf0A==
.unpackedSize: 2.3 MB

dependencies:
@langchain/langgraph-checkpoint: ^1.0.0 langsmith: ~0.3.74 zod: ^3.25.76 || ^4
@langchain/langgraph: ^1.0.0 uuid: ^10.0.0

maintainers:

• christian-bromann [email protected]
• nfcampos [email protected]
• jacoblee93 [email protected]
• andrewnguonly [email protected]
• davidduong [email protected]
• hntrl [email protected]
• hwchase17 [email protected]
• basproul [email protected]

dist-tags:
latest: 1.1.1 alpha: 1.0.0-alpha.9
next: 1.0.0-alpha.9 tag-for-publishing-older-releases: 0.2.20

published 22 hours ago by GitHub Actions [email protected]

node --version
v25.2.1