Cursor rules vs Copilot instructions 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.

Measured — counted from real repositories, nightlyAsserted — read from the vendor docs, dated

CompareAGENTS.md CLAUDE.md Cursor rules Copilot instructions Cline rules GEMINI.md .cursorrules Windsurf rulestwo to five

Format	Cursor rules 2026-08-02	Copilot instructions 2026-08-01	Cline rules 2026-08-01
Asserted — what the docs say it can express
File	.cursor/rules/*.mdc	.github/copilot-instructions.md	.clinerules
Status	vendor	vendor	vendor
Cross-tool	No	No	No
Tools that read it	Cursor	GitHub Copilot Copilot coding agent VS Code	Cline Roo Code
Frontmatter	Yes	Yes	No
Glob targeting	Yes	Yes	No
Imports other files	Yes	No	No
Nested / per-directory	Yes	No	No
Multiple files	Yes	Yes	Yes
User-level scope	No	No	Yes
When it applies	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.	copilot-instructions.md is always in scope. Additional .github/instructions/*.instructions.md files load when their applyTo glob matches the open file.	Always in scope. Either a single .clinerules file or a .clinerules/ directory whose markdown files are all loaded.
Size limits	None	None	None
Measured — counted from real repositories on 2026-08-04
Repositories carrying it	179	126	79
Share of indexed repos	25.6%	18.1%	11.3%
Files indexed	1,280	309	305
Median length (words)	272	417	262
90th percentile length	1,170	1,299	1,412
Files naming commands	29.4%	41.4%	34.1%
Files containing code	58.0%	48.2%	33.1%
Median quality score	52	60	54
Median repository stars	24	18,123	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.

Cursor rules + Copilot instructions

2026-08-04

repositories carry both. That is 16.2% of everything with Cursor rules, and 23.0% of everything with Copilot instructions.

Cursor rules + Cline rules

2026-08-04

repositories carry both. That is 7.8% of everything with Cursor rules, and 17.7% of everything with Cline rules.

Copilot instructions + Cline rules

2026-08-04

repositories carry both. That is 15.9% of everything with Copilot instructions, and 25.3% of everything with Cline rules.

What each one is for

Cursor rules

2026-08-02

The 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

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Copilot instructions

2026-08-01

Two layers: one always-on repo file, plus optional glob-scoped instruction files. Lives under .github/ rather than the repo root, which is the tell that it is aimed at the GitHub platform surface as much as the editor.

Strengths

Reaches Copilot across the editor, github.com and the coding agent from one file
applyTo globs give per-path targeting without leaving the .github convention

Weaknesses

Copilot-only
No imports; shared text is copied between instruction files
Buried under .github/, so contributors discover it less often than a root file

Full page Browse 309 files

Cline rules

2026-08-01

A 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

Full page Browse 305 files