AGENTS.md
A plain-markdown README for coding agents, deliberately unopinionated: no frontmatter, no globs, no vendor keys. That minimalism is why it became the one file a dozen different agents will read, and why it carries the least per-file targeting power of any format here.
What the corpus measured
2026-08-03Repositories
396
2026-08-03Adopting repositories, not files.Share of corpus
57.0%
2026-08-03Of every repository RuleStack indexes.Median length
954w
2026-08-0390th percentile 2,955 words.Median quality
52
2026-08-0342.9% name a command; 36.5% contain code.Repositories carrying AGENTS.md, 2026-08-01 to 2026-08-03
Real AGENTS.md files
| Repository | Format | Stack | Covers | Score | Changed |
|---|---|---|---|---|---|
| n8n-io/n8npackages/@n8n/agents/AGENTS.md · 199k | AGENTS.md | buildteststylearch+3 | 100/100 | 3 days ago | |
| mui/material-uiAGENTS.md · 99k | AGENTS.md | setupbuildtestlint-format+9 | 100/100 | 3 days ago | |
| vllm-project/vllmAGENTS.md · 88k | AGENTS.md | setuptestlint-formatstyle+5 | 100/100 | 3 days ago | |
| elastic/elasticsearchx-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/AGENTS.md · 78k | AGENTS.md | buildtestlint-formatstyle+2 | 100/100 | 3 days ago | |
| elastic/elasticsearchx-pack/plugin/inference/AGENTS.md · 78k | AGENTS.md | buildtestlint-formatstyle+3 | 100/100 | 3 days ago | |
| code-yeongyu/oh-my-openagentpackages/web/AGENTS.md · 67k | AGENTS.md | setupbuildtestlint-format+6 | 100/100 | 2 days ago | |
| rails/railsAGENTS.md · 59k | AGENTS.md | teststylearchgit+4 | 100/100 | 3 days ago | |
| TryGhost/Ghoste2e/AGENTS.md · 55k | AGENTS.md | setupteststylearch+2 | 100/100 | 3 days ago | |
| aaif-goose/gooseAGENTS.md · 52k | AGENTS.md | setupbuildtestlint-format+6 | 100/100 | 3 days ago |
What it asserts
2026-08-02Read from the format’s own documentation and checked by hand. Capabilities are asserted; adoption is measured.
- File
- AGENTS.md
- When it applies
- Always in scope; in a monorepo the nearest AGENTS.md to the edited file wins.
- Size limits
- None documented
- Tools that read it
- OpenAI CodexCursorAmpAiderZedGoogle JulesGemini CLIFactoryRooCodeopencodeDevinWarpgooseVS CodeGitHub Copilot coding agentWindsurfJunie (JetBrains)Kilo CodeAugment CodeUiPath AutopilotSemgrepPhoenixOna
Capabilities
- Read by more than one tool
- Frontmatter
- Glob targeting
- Imports other files
- Nested / per-directory
- Multiple files
- User-level scope
Strengths
- Read by more agents than any other format — one file covers most of a team's tooling
- No schema to get wrong; a plain markdown file always parses
- Nested files let a monorepo scope instructions per package
Weaknesses
- No glob targeting — every rule is loaded for every file, spending context
- No imports, so shared rules must be duplicated across packages
- No frontmatter means no machine-readable metadata for tooling to act on
Measured — counted from real repositories, nightlyAsserted — read from the vendor docs, dated
Repositories that carry AGENTS.md and something else
Counted pairwise across the whole corpus. The percentage is of repositories carrying AGENTS.md — the number a “AGENTS.md vs …” search is really asking for.
+ CLAUDE.md
31.8%
2026-08-03126 repos carry both50.8% the other way
+ Copilot instructions18.7%
2026-08-0374 repos carry both58.7% the other way
+ Cursor rules17.2%
2026-08-0368 repos carry both38.0% the other way
+ Cline rules6.6%
2026-08-0326 repos carry both32.9% the other way
+ GEMINI.md5.8%
2026-08-0323 repos carry both69.7% the other way
+ Windsurf rules2.5%
2026-08-0310 repos carry both71.4% the other way
+ .cursorrules2.5%
2026-08-0310 repos carry both37.0% the other way
