AGENTS.md vs CLAUDE.md vs Cursor rules vs Windsurf rules vs Cline rules
Every comparison page on the web is a capability table someone wrote from the vendor docs in an afternoon. None of them can tell you how many real repositories ship each file, how long the median one runs, or how often two of them turn up in the same project. Those answers need a corpus, and RuleStack counts one every night.
| Format | AGENTS.md 2026-08-02 | CLAUDE.md 2026-08-02 | Cursor rules 2026-08-02 | Windsurf rules 2026-08-01 | Cline rules 2026-08-01 |
|---|---|---|---|---|---|
| Asserted — what the docs say it can express | |||||
| File | AGENTS.md | CLAUDE.md | .cursor/rules/*.mdc | .windsurf/rules/*.md | .clinerules |
| Status | open-standard | vendor | vendor | vendor | vendor |
| Cross-tool | Yes | No | No | No | No |
| Tools that read it |
|
|
|
|
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| Frontmatter | No | No | Yes | Yes | No |
| Glob targeting | No | No | Yes | Yes | No |
| Imports other files | No | Yes | Yes | No | No |
| Nested / per-directory | Yes | Yes | Yes | No | No |
| Multiple files | Yes | Yes | Yes | Yes | Yes |
| User-level scope | No | Yes | No | Yes | Yes |
| When it applies | Always in scope; in a monorepo the nearest AGENTS.md to the edited file wins. | Always in scope. Project file, plus nested files in subdirectories, plus a user-level file (~/.claude/CLAUDE.md) that applies across every project. | Four modes set in frontmatter: Always Apply (every chat session), Apply Intelligently (the agent picks it by description), Apply to Specific Files (globs match the edited file), and Apply Manually (@-mentioned). Rules must carry the .mdc extension — a plain .md file in .cursor/rules is ignored. | Four trigger modes in frontmatter: always_on, glob, model_decision, manual. The legacy single-file .windsurfrules is still read. | Always in scope. Either a single .clinerules file or a .clinerules/ directory whose markdown files are all loaded. |
| Size limits | None | None | None | Per-rule and total character caps apply; long rules are truncated rather than rejected. | None |
| Measured — counted from real repositories on 2026-08-04 | |||||
| Repositories carrying it | 399 | 248 | 179 | 14 | 79 |
| Share of indexed repos | 57.2% | 35.5% | 25.6% | 2.0% | 11.3% |
| Files indexed | 1,373 | 775 | 1,280 | 102 | 305 |
| Median length (words) | 953 | 2,042 | 272 | 515 | 262 |
| 90th percentile length | 2,956 | 2,998 | 1,170 | 1,518 | 1,412 |
| Files naming commands | 42.8% | 34.2% | 29.4% | 37.3% | 34.1% |
| Files containing code | 36.0% | 34.5% | 58.0% | 70.6% | 33.1% |
| Median quality score | 52 | 44 | 52 | 58 | 54 |
| Median repository stars | 9,402 | 114 | 24 | 119 | 1 |
How often they turn up together
A capability table cannot answer this at all. Of the repositories carrying the first format, this is the share that also carry the second — counted, both directions, on 2026-08-04.
Windsurf rules + Cline rules
2026-08-048
repositories carry both. That is 57.1% of everything with Windsurf rules, and 10.1% of everything with Cline rules.
Cursor rules + Windsurf rules
2026-08-0412
repositories carry both. That is 6.7% of everything with Cursor rules, and 85.7% of everything with Windsurf rules.
Cursor rules + Cline rules
2026-08-0414
repositories carry both. That is 7.8% of everything with Cursor rules, and 17.7% of everything with Cline rules.
CLAUDE.md + Windsurf rules
2026-08-047
repositories carry both. That is 2.8% of everything with CLAUDE.md, and 50.0% of everything with Windsurf rules.
CLAUDE.md + Cursor rules
2026-08-0455
repositories carry both. That is 22.2% of everything with CLAUDE.md, and 30.7% of everything with Cursor rules.
CLAUDE.md + Cline rules
2026-08-0425
repositories carry both. That is 10.1% of everything with CLAUDE.md, and 31.6% of everything with Cline rules.
AGENTS.md + Windsurf rules
2026-08-0410
repositories carry both. That is 2.5% of everything with AGENTS.md, and 71.4% of everything with Windsurf rules.
AGENTS.md + Cursor rules
2026-08-0468
repositories carry both. That is 17.0% of everything with AGENTS.md, and 38.0% of everything with Cursor rules.
AGENTS.md + Cline rules
2026-08-0426
repositories carry both. That is 6.5% of everything with AGENTS.md, and 32.9% of everything with Cline rules.
AGENTS.md + CLAUDE.md
2026-08-04126
repositories carry both. That is 31.6% of everything with AGENTS.md, and 50.8% of everything with CLAUDE.md.
What each one is for
AGENTS.md
2026-08-02A 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.
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
CLAUDE.md
2026-08-02Claude Code's memory file. Shaped like AGENTS.md but with two things it lacks: @path imports, so shared rules live in one place, and a user-scope layer that follows the developer across repos rather than shipping with the code.
Strengths
- @path imports — shared conventions written once and pulled into each file
- A user-scope file lets personal preferences live outside the team repo
- Nested project files compose with the root file rather than replacing it
Weaknesses
- Single-vendor: no other agent reads it, so multi-tool teams maintain two files
- No glob targeting, same context cost as AGENTS.md — path-scoped rules exist, but in a separate .claude/rules/ file, not in CLAUDE.md itself
Cursor rules
2026-08-02The most expressive format here. Many small .mdc files, each with frontmatter declaring when it should load, so a rule about migrations only enters context when a migration is open. Costs the most to maintain and only one editor reads it.
Strengths
- Glob-scoped activation — the only widely-used format that keeps unrelated rules out of context
- Description-based activation lets the agent pull a rule in on demand
- Many small files are easier to review in a PR than one growing document
Weaknesses
- Cursor-only
- Frontmatter is a schema, and a malformed .mdc silently stops applying
- Fragmentation: rules spread over many files are easy to duplicate and contradict
Windsurf rules
2026-08-01Cursor's activation model with a different vocabulary — trigger modes instead of rule types — plus hard character caps, which is the one place a format here will silently drop instructions rather than fail loudly.
Strengths
- Trigger modes give the same glob and on-demand targeting as Cursor rules
- Workspace and global rule scopes
Weaknesses
- Windsurf-only
- Character caps truncate silently — a long rule can be half-applied with no error
- No imports
Cline rules
2026-08-01A single file or a folder of files, all always-on. The folder form is the simplest way any format here lets you split rules into topics without also learning an activation model.
Strengths
- Directory form splits rules by topic with zero configuration
- Toggleable rule sets for switching context between tasks
Weaknesses
- Cline-only
- Everything is always-on — no targeting, so the folder form costs context
