Every "awesome skills" list tells you a skill is good. Few show the source footprint, install tradeoffs, or what real users report after installing it.
New reviews use the skill source, repository metadata, public issue history, commit history, and direct community links. Legacy August 24-25 entries remain marked as measured runs.
Context figures in new reviews are labelled as file-size estimates: bytes divided by four. They are not measured bills and do not come from private traffic.
Dollar figures use published list pricing: Claude Sonnet 5 at $2 per million input tokens and $10 per million output tokens, Claude Opus 5 at $5 and $25, Claude Haiku 4.5 at $1 and $5. Multi-turn sessions re-send history each turn, so input tokens grow with conversation length. That's included in our totals.
A 12,493-byte web-app security checklist from ECC, plus a 10,171-byte cloud security companion. We read the source and public GitHub issue history instead of running it through our API.
243,763 stars · 286 README-listed skills · verdict: useful checklist, real harness caveatsA 9,465-byte root-cause debugging skill from the Superpowers framework. We read the full 40,772-byte directory and public issue history instead of running it through our API.
278,122 stars · 14 skills · verdict: strong discipline with real activation rough edgesAnthropic's own API reference skill ships a 75,707-byte SKILL.md and a 973,337-byte source set. We read the source and the issue tracker instead of running it through our API.
171,582 stars · 20 skills · verdict: authoritative docs with real context-risk complaintsA 3,549-byte skill that enforces red-green-refactor one slice at a time. We drove a five-round session adding a coupon feature and measured every turn against an unguided control arm.
5-round session 28,214 tokens · $0.074 on Sonnet 5The most popular skill in a 234,000-star repo is 1,987 bytes of markdown that makes the agent interrogate you before it writes code. We ran a four-round session on a real feature spec and measured every turn.
4-round session 13,519 tokens · $0.037 on Sonnet 5| Skill | Source | Evidence base | Context / tokens | Signal | Criticism |
|---|---|---|---|---|---|
security-review | affaan-m/ECC | source + GitHub issue signals | 12,493 B SKILL.md; ~3,123 est. tokens | 243,763 stars; 286 README-listed skills | broad checklist; framework has real security/install-surface caveats |
systematic-debugging | obra/superpowers | source + GitHub/HN signals | 9,465 B SKILL.md; ~2,366 est. tokens | 278,122 stars; 14 skills | rigid process can become noise on mechanical fixes |
claude-api | anthropics/skills | source + GitHub issues | 75,707 B SKILL.md; ~18,927 est. tokens | 171,582 stars; 20 skills | broad trigger can waste context |
tdd | mattpocock/skills | legacy measured run | 28,214 measured tokens | 5-round session | not cheaper than control |
grilling / grill-me | mattpocock/skills | legacy measured run | 13,519 measured tokens | 4-round session | can be overhead on trivial tasks |
More skills land here daily. New reviews use source code, public GitHub signals, and attributed community reports rather than private traffic measurements.
Skills are markdown files that get injected into the agent's context. A big skill is a big prompt, and a skill that runs in rounds re-sends its own instructions on every turn. Two skills can look equally useful in a README and differ by 10x in what they bill you.
That gap is invisible until someone measures it. So we measure it. If you want to check our numbers against your own workload, the API cost calculator and token counter are free and need no signup.