Claude Code had been sending some MCP tool calls twice. Version 2.1.307 stops it.

By Lior AharonovFounder, 7IT Solutions · 21 October 2026

What happened

Claude Code 2.1.307, published to npm on 21 October 2026 at 20:47 UTC, fixes HTTP MCP tool calls that were sent twice when the connection closed mid-call. Per the changelog, only read-only or idempotent tools are now retried, and servers no longer stay failed in headless runs after a macOS or Linux computer slept while they were connecting.

Why it matters

A tool that charges a card, sends an email or opens a ticket could have run twice on one request. Retries now depend on whether a tool is read-only or idempotent, which MCP tools declare with the readOnlyHint and idempotentHint annotations.

What to do

Check the readOnlyHint and idempotentHint annotations on every tool you publish, and set them only where a repeated call is truly harmless.

A retry is a second request with your name on it. Only promise idempotent if you mean it.

Lior Aharonov · my take

Sources

Claude Code changelog, v2.1.307 (Anthropic on GitHub) raw.githubusercontent.com
@anthropic-ai/claude-code 2.1.307 (npm registry) registry.npmjs.org

claude-coderetriesannotationsclients

Researched with AI tools; every fact is checked against the linked sources.