Intel / article

Quoting Thariq Shihipar

Source: simonwillison.net
Date: Published Sep 18, 2026

Context

Anthropic's Claude Code can use AGENTS.md project instructions, a file some other coding tools read. The September 18 announcement, quoted by Simon Willison, introduced support as a fallback: in version 2.1.277, if a folder has no CLAUDE.md, Claude checks for and uses AGENTS.md.

The current built-in module documentation specifies the default more precisely: a project CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md along the path to the working directory suppresses that fallback. A separate option loads both formats. Consequently, adding AGENTS.md to a project that already has Claude-specific instructions does not automatically mean both sets will be read.

Key takeaways · AI-distilled

Claude Code checks for an AGENTS.md file when a folder has no CLAUDE.md, starting in version 2.1.277, per Thariq Shihipar.
AGENTS.md support ships as a built-in "Claude Code mod," part of an upcoming system for customizing the Claude Code itself.
Beyond this built-in mod, users will be able to build their own custom mods to customize project instructions for their own workflow.

Terms in this piece · Glossary

agent harness — The scaffolding around a model that turns it into a working agent — the loop, the tools it can call, and the rules for when to stop.

Read the source simonwillison.net