API Error 400: tool_use ids must be unique - occurs consistently

Claude Code version: 2.1.20

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/21094
2. https://github.com/anthropics/claude-code/issues/20751
3. https://github.com/anthropics/claude-code/issues/20583

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II don't think its either of those reports - might have the same root cause, but in my case im not using multi-turn and im not using stream-json -- my use case is a simple --print with --output-format=json (or even in interactive mode with no --print or --output-format at all)

one more thing I might add - the tool use actually goes though - the action in the tool use is performed and then the 400 happens

<img width="617" height="251" alt="Image" src="https://github.com/user-attachments/assets/d2ec1815-6e2a-49a6-ac65-b68af18c4efe" /> - this literally happened when I was reporting this very but and the comment was indeed posted ;)

FYI - it's not related to the VSCode extension - this happens both in CLI and in the VSCode plugin ( I saw some issues regarding the VSCode extension )

Having the same Issue 2 weeks ago in my code sessions in web, app, and desktop, i cant find a solution, even claude say it is a bug when asked. I reduced the size of files like claude.md and PRD files, but this is consistent.

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.13.content.3: tool_use ids must be unique"},"request_id":"req_011CYLadytJmjDoyKkbJh8rD"}

I have the same issue in claude code online. Did anyone find a way to recover from this error?

Still experiencing this on v2.1.50 in interactive desktop mode on Windows 11.

Error

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.9.content.1: tool_use ids must be unique"}}

The error repeats on every retry (6+ times observed), creating an infinite loop since the corrupted message history is resent each time.

Trigger

• Parallel tool calls where some fail with "Sibling tool call errored"
• Specifically triggered by an Explore subagent performing broad filesystem searches from C:\ root
• Multiple parallel Glob/Grep/Read calls are launched, several fail, and the resulting message construction produces duplicate tool_use IDs

Note on the v2.1.21 fix

The fix described as "Fixed API errors when resuming sessions that were interrupted during tool execution" appears to have only resolved the --print mode variant (confirmed by @waihaiwai in #20751). The interactive/desktop mode variant with parallel tool call failures is still present through v2.1.50.

Workaround

/clear or start a new session. The corrupted conversation history is what causes the retry loop — once cleared, the error stops. Setting the working directory to the actual project folder (not C:\) reduces the likelihood of triggering it.

running /clear on Claude Web/Android doesn't work, endless loop.

As soon as I installed/started using claude desktop on windows, I started getting these random "API Error 400: tool_use ids must be unique" errors via remote-control to a claude-code tui install that never generates those errors

Closing for now — inactive for too long. Please open a new issue if this is still relevant.

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.