# How often agent files change: 31,009 files over four weeks

By markdownregistry. Published October 8, 2026. Updated October 8, 2026.

About a quarter of the agent files we followed changed within four weeks of our first read. Of 31,009 SKILL.md, AGENTS.md, CLAUDE.md, DESIGN.md, Cursor rule and llms.txt files in public GitHub repositories, 7,968 (25.7%) had a new version within 28 days. Among changed skills with a description in both versions, 31.9% changed the description, the text an agent reads to decide whether to load the skill.

| File | Files compared | Changed in 4 weeks | Share |
| --- | --- | --- | --- |
| llms.txt | 172 | 84 | 48.8% |
| AGENTS.md | 1,941 | 739 | 38.1% |
| CLAUDE.md | 855 | 257 | 30.1% |
| SKILL.md | 27,311 | 6,816 | 25.0% |
| Cursor rules | 206 | 37 | 18.0% |
| DESIGN.md | 524 | 35 | 6.7% |
| All six | 31,009 | 7,968 | 25.7% |

Agent files in public GitHub repositories that the registry first read before September 10, 2026, and checked again at least 28 days later, and how many had a commit dated within 28 days of that first read. Read on October 8, 2026. How each was counted is under How we counted.

Counted from the registry's own version history of public GitHub, read on October 8, 2026.

## Why a copy goes stale

Most agent files reach a project as a copy: a skill folder dropped into `.claude/skills/`, an AGENTS.md borrowed from a project you admire, a Cursor rule pasted from a gist. The copy stays as it was the day you took it. The original keeps moving, and nothing tells you when it does. The registry keeps every version of each file it collects, keyed by the SHA-256 of its content, so it can say how often the original moves.

We took the 31,029 files the registry first read before September 10, 2026 and checked again at least 28 days later, so that a change inside those 28 days would have been seen. For each, the version that was current at the first read is the copy you would have taken that day. A file changed when its repository committed a new version of it within the next 28 days.

## 25.7% changed in four weeks

Across all six kinds, 7,968 of 31,009 files changed. llms.txt files changed most often, 48.8% of 172, which fits files that list a website's documentation and follow it as it changes. AGENTS.md followed at 38.1%, then CLAUDE.md (30.1%) and SKILL.md (25.0%). Cursor rules changed in 18.0% of 206 files, though 29.7% of those changes came from one repository. DESIGN.md changed least, 6.7%.

The SKILL.md share is not one busy project. The 6,816 changed skills sit in 647 repositories, and the largest accounts for 1.4% of them. Changes also come in runs: half the changed skills had 2 or more new versions in the four weeks, and 2,304 had three or more. Those counts are a lower bound, because the crawler records at most five new commits to a file on each visit.

## Skills: the description moves too

The Agent Skills specification has an agent load the `name` and `description` of every installed skill at startup, and read the rest of SKILL.md only once it decides to use the skill. So a change to the description changes when the skill is used, not only what it says. Of the 6,787 changed skills that carry a description in both versions, 2,166 (31.9%) changed it within the four weeks. Names were steadier: 39 changed skills changed or added a name.

A copy taken on the first day keeps the old description. If the original learned to say when it should be used, or narrowed what it claims to do, the copy does not know.

## Files mostly grow

Changed files got longer more often than shorter. Of the changed skills, 4,981 grew and 1,684 shrank, with a median change of 3.1% in bytes. AGENTS.md files grew in 644 of 739 cases, by a median of 10.6%, and CLAUDE.md files by 3.7%. The registry's audit grade, its own deterministic checks of each version, rarely moved: across all six kinds, 53 changed files graded higher in their newer version and 54 graded lower.

## Check a file you copied

If you know the repository and path a copy came from, git can list what changed there since you took it. In a clone of the original, the first command lists each commit to the file since a date; the second prints only the lines where a SKILL.md description changed. This is the output in a scratch repository whose skill was added on September 8 and changed twice after September 10:

```
$ git log --since=2026-09-10 --format='%cs %s' -- skills/report/SKILL.md
2026-10-02 Add a build step
2026-09-21 Say when to use the report skill
$ git log -p --since=2026-09-10 -- skills/report/SKILL.md | grep '^[-+]description:'
-description: Builds a weekly report.
+description: Builds a weekly report. Use when the user asks for a status summary.
```

To stop guessing, install the file pinned to a content hash and check for changes on purpose: [how to pin an agent skill](https://markdownregistry.com/guides/pin-agent-skills) walks through it with real output, and [the skill security guide](https://markdownregistry.com/guides/agent-skill-security) covers what to read in a new version before you take it. Every file the registry collects shows its version history on its own page, starting from [the SKILL.md page](https://markdownregistry.com/kind/skill). To start a new one from a file that passes every check the registry runs, use [the SKILL.md starter on mdpantry](https://mdpantry.com/s/st_shjaxurgoqng23jq), which says what to change in it.

## How we counted

The registry collects agent markdown from public GitHub repositories. On a file's first read it records a version for each of the five most recent commits to that file; on each later visit it records a version for each new commit, up to five per visit, every version keyed by the SHA-256 of its content and dated by its commit. A file counts when the registry first read it before September 10, 2026, and checked it again at least 28 days after that first read, with no error on its repository's latest crawl; 31,029 files qualified. A visit to a repository reads at most 200 agent files and records at most 25 changed ones, so a file past those limits counts only if a later visit checked it at least 28 days after its first read. Files the registry has marked deleted upstream are left out. The version current at the first read is the newest one dated at or before it; 20 files whose recorded commits all postdate the first read have nothing to compare against and were left out, which leaves the 31,009 counted here. A file changed when a version is dated after the first read and no more than 28 days after it. Dates are commit dates as git records them. Versions are keyed by their content, so a change the registry recorded still counts even if it was later undone, while a change back to content the file once had adds no version; with the five-commit limit, that can hide a change, so read every share here as a lower bound. For SKILL.md files, the `name` and `description` in the frontmatter of the version current at the first read are compared, after trimming spaces, with those of the last version inside the window. Size is the file's length in bytes. The registry finds most repositories through GitHub searches for repositories tagged with agent skill or Claude Code topics, or whose README mentions SKILL.md, with a minimum star count and sorted by recent activity, which is why SKILL.md files dominate the sample and why the files it follows lean toward starred projects that are being worked on; read the shares as describing those repositories, not every file on GitHub.

## Sources

- [Agent Skills specification: how skills load, name and description](https://agentskills.io/specification)

Last checked October 8, 2026. The page: https://markdownregistry.com/blog/how-often-agent-files-change