RuleStack
Counted 08:17 UTC

Real files, at real paths, counted every night

RuleStack
Real files, at real paths, counted every nightCounted 08:17 UTCDiff two files
7,205instruction files1,198repositories visited4,189rows written36files changed8formats20section tags85stacksCounted 13 September 2026
AGENTS.md617 repos, 60.4%CLAUDE.md359 repos, 35.2%.cursor/rules/*.mdc310 repos, 30.4%.github/copilot-instructions.md190 repos, 18.6%.clinerules188 repos, 18.4%GEMINI.md48 repos, 4.7%.windsurf/rules/*.md38 repos, 3.7%.cursorrules36 repos, 3.5%

AGENTS.md is in 617 repositories. The median one runs 857 words.

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.

No vendor, open standardopen standardSince 2025-08-01All 2,031 indexed files
Measured

What the nightly counted in real repositories

Counted 13 September 2026
Repositories carrying it617 60.4% of the corpus
Files that write down a command49.1%
Files carrying a code block40.8%
Code style71.9% of 558 root files
Agent behaviour62.4% of 558 root files
Tests59.9% of 558 root files
Hard prohibitions55.7% of 558 root files
Git, commits & PRs53.6% of 558 root files
Architecture45.3% of 558 root files
Lint & format43.0% of 558 root files
Build40.0% of 558 root files
Setup & install33.2% of 558 root files
Documentation29.9% of 558 root files
Security24.7% of 558 root files
Testing strategy21.3% of 558 root files
Types19.0% of 558 root files
APIs & contracts17.6% of 558 root files
Deploy & release15.2% of 558 root files
UI & components13.6% of 558 root files
Dependencies13.4% of 558 root files
Performance10.0% of 558 root files
Database & migrations9.5% of 558 root files
Monorepo5.9% of 558 root files
Every night counted

Repositories carrying AGENTS.md, one column a night

24 nights stored
2026-08-01326 to 617 repositories2026-09-13
Asserted

What the documentation says this file can express

Read 2 August 2026
FileAGENTS.md
OwnerNo vendor, open standard
Tools that read it23 tools
Glob targetingNo
ImportsNo
FrontmatterNo
Nested filesYes
User scopeNo

Read from the format’s own documentation and checked by hand. Capabilities are asserted; adoption is measured.

Always in scope; in a monorepo the nearest AGENTS.md to the edited file wins.

OpenAI CodexOpenAI CodexCursorCursorAmpAmpAiderAiderZedZedGoogle JulesGoogle JulesGemini CLIGemini CLIFactoryFactoryRoo CodeRooCodeopencodeopencodeDevinDevinWarpWarpgoosegooseVS CodeVS CodeGitHub CopilotGitHub Copilot coding agentWindsurfWindsurfJunie (JetBrains)Junie (JetBrains)Kilo CodeKilo CodeAugment CodeAugment CodeUiPath AutopilotUiPath AutopilotSemgrepSemgrepPhoenixPhoenixOnaOna
What it does well
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
What it cannot do
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
Counted pairwise

Repositories that carry AGENTS.md and something else

Counted 13 September 2026

The percentage is of repositories carrying AGENTS.md, which is the number a “AGENTS.md versus something” search is really asking for.

CLAUDE.md33.5%207 carry both, 57.7% the other wayCursor rules25.8%159 carry both, 51.3% the other wayCopilot instructions19.8%122 carry both, 64.2% the other wayCline rules12.8%79 carry both, 42.0% the other wayGEMINI.md6.5%40 carry both, 83.3% the other wayWindsurf rules4.7%29 carry both, 76.3% the other way.cursorrules2.6%16 carry both, 44.4% the other way
The files

2,031 AGENTS.md files match in the corpus. These score highest.

All 2,031
NoRepository and pathCoversScoreChanged
001TypeScriptn8n-io/n8npackages/@n8n/agents/AGENTS.md100 /1004 days ago002JavaScriptmui/material-uiAGENTS.md100 /10023 days ago003Pythonvllm-project/vllmAGENTS.md100 /10023 days ago004Javaelastic/elasticsearchx-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/AGENTS.md100 /1001 month ago005TypeScriptcode-yeongyu/oh-my-openagentpackages/web/AGENTS.md100 /10019 days ago006Rubyrails/railsAGENTS.md100 /1001 month ago007Rustaaif-goose/gooseAGENTS.md100 /1002 days ago008Goethereum/go-ethereumAGENTS.md100 /1001 month ago009Rubywpscanteam/wpscanAGENTS.md100 /1001 month ago010PythonModelEngine-Group/nexentAGENTS.md100 /10015 days ago011PythonOnlyTerp/prompt-cache-skillsAGENTS.md100 /1001 month ago012Pythonunoplat/unoplat-code-confluenceunoplat-code-confluence-frontend/AGENTS.md100 /10023 days ago
The ten best, annotated