"tool_use ids were found without tool_result blocks" on a saved thread

An agent with a database checkpointer fails on every new message in one thread with a tool_use/tool_result mismatch error.

Difficulty

Moderate

Time

~15 min

Steps

Fixed in

—

Last checked

2026-10-15

Unverified: we could not confirm from the sources that a fix shipped. Source: issue closed as completed, no linked fix. Last checked 2026-10-15.

Symptom

An agent with a database checkpointer fails on every new message in one thread with a tool_use/tool_result mismatch error.

Evidence what you'll see

The same code works on a fresh thread_id
An earlier run on that thread was interrupted partway through a tool call

Cause

The saved checkpoint holds an assistant message with tool calls but no matching tool results, so the history is invalid each time it is reloaded.

Fix steps

0 of 3 done

Step 1Re-run with a new thread_id. If that works, the stored thread is corrupted.
Step 2Delete or repair the bad thread's checkpoints. Check which columns your schema uses to identify a thread before deleting.
Step 3Make sure interrupted tool calls always get an error tool message written back (see the related cancelled-tool guide).

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Verify the fix worked

The original thread, or its replacement, accepts new messages without the error.

Did this fix it?

Sources and credit

Summarized in our own words from these public reports. Credit goes to their authors.

langgraph issue #5109 ↗

Provided as is, without warranty. Test in a non-production environment and back up first. Security-related steps: verify against the official docs. Terms · Request removal or attribution change