Claude Code's new /checkup deletes unused skills. These are the ones developers keep

Claude Code shipped a new command this morning, and it is basically a diet plan for your agent setup.

Boris Cherny announced /checkup on July 9, and the post passed 115,000 views within hours. The pitch is simple: your Claude Code install has accumulated cruft, and /checkup cleans it. From his list, it will:

1. Clean up unused skills, MCPs and plugins to save context
2. Dedup your local CLAUDE.md against the checked-in CLAUDE.md
3. Break up a large root CLAUDE.md into nested CLAUDE.md files plus skills
4. Turn off slow hooks
5. Update Claude Code to the latest version
6. Enable auto mode by default
7. Pre-approve frequently denied read-only commands

It confirms with you before changing anything. The 2.1.205 changelog frames it as /doctor growing into "a full setup checkup that can diagnose and fix issues", with /checkup as its alias.

Why unused skills are not free

The interesting part is item 1. Skills feel free because they sit on disk until triggered. They are not. Every installed skill contributes its name and description to what the model reads when deciding what to load, so a pile of skills you never use costs tokens on every session and makes routing worse: two skills with overlapping descriptions can silently steal each other's triggers.

Anthropic building deletion into a first-party command is a strong signal. The ecosystem phase where you install 50 skills to feel prepared is ending. The question that matters now is the opposite one: which skills actually earn a permanent slot?

The skills that survive a /checkup

Install counts answer that better than any listicle, because an install that survives cleanup week after week reflects real use. The data below is from the Skillselion live catalog, refreshed daily from skills.sh, GitHub and MCP registries, ranked by real installs (checked today, July 9).

1. find-skills (vercel-labs/skills) - 2,402,309 installs. A meta-skill that discovers and loads other skills on demand. It is the /checkup philosophy productized: install one small router, load everything else mid-task, keep nothing resident.
2. frontend-design (anthropics/skills) - 640,200 installs. Anthropic's own skill for building interfaces that do not look AI-generated. Fires on a huge share of real sessions, which is exactly why it survives.
3. vercel-react-best-practices (vercel-labs/agent-skills) - 535,433 installs. Framework guidance the model would otherwise guess at. If you write React weekly, this triggers weekly.
4. agent-browser (vercel-labs/agent-browser) - 524,998 installs. Gives the agent a browser for verifying its own frontend work. Capability skills like this cannot be replaced by a better prompt.
5. grill-me (mattpocock/skills) - 486,725 installs. Matt Pocock's plan stress-tester: it interviews you about your design until the gaps show. A workflow skill, not a knowledge skill, and one of the few that developers keep.
6. web-design-guidelines (vercel-labs/agent-skills) - 447,981 installs. Design review against concrete guidelines instead of vibes.
7. remotion-best-practices (remotion-dev/skills) - 415,415 installs. Narrow, single-domain, maintained by the vendor. The exact shape of skill that never gets flagged as cruft.
8. tdd (mattpocock/skills) - 381,925 installs. Enforces test-first discipline on the agent. Process skills survive because they change behavior on every coding task, not just some.

One bundle deserves its own mention: microsoft/azure-skills (GitHub) ships 16 skills that each sit between roughly 380,000 and 440,000 installs. Vendor bundles ride together: teams deploying on Azure install the whole set and keep the whole set.

The pattern

Three traits separate keepers from cruft:

• They trigger weekly, not theoretically. Framework and process skills fire on ordinary work. The conference-demo skill you installed in March does not.
• They are narrow. A skill that does one job has a precise description, so the router finds it reliably. Kitchen-sink orchestrator skills are the first thing /checkup should eat.
• They either know something or do something. Vendor-maintained knowledge (React, Remotion, Azure) or a real capability (a browser). Skills that merely rephrase what the model already knows do not survive contact with a cleanup pass.

Run the numbers on your own setup

You do not need to wait for /checkup to reach your version. Ask Claude Code to list your installed skills, then ask which of them actually fired in your last twenty sessions. Anything at zero is a candidate. Keep the router-style discovery skill, keep what fires weekly, cut the rest, and let install-ranked data arbitrate what is worth re-adding: the full ranked catalog is at skillselion.com/skills.

I run Skillselion, a directory of Claude Code, Codex and Cursor extensions ranked by real installs. Install counts above are from the live catalog, checked July 9, 2026.