# SkillBill by AIR

> Paste a skill. AIR checks it for security risks, builds a cheaper version and runs both on the same tasks. You keep the new one only if it does the same job for fewer tokens.

SkillBill is a free web tool and public API from AIR for agent skills: the SKILL.md files and folders that tell an AI agent such as Claude Code how to do a job. It reviews a skill for security risks and measures whether a cheaper version does the same job with fewer tokens.

When to use SkillBill:

- Before installing an agent skill (a SKILL.md and its folder) from someone else, to see what it can reach and whether its security review is clear.
- When a skill your agent runs often costs too many tokens, to get a cheaper version that was measured doing the same job on the same tasks.
- When choosing between published skills, to compare the measured results on the skill pages.

When not to use it:

- To run a skill or an agent for you. It checks and measures skills; it does not host them.
- To judge whether a skill is useful at all. It compares a skill with its own optimized version, not with having no skill.
- For prompts, models or MCP servers that are not agent skills.

How an agent should call it: POST a skill to https://skillbill.sh/v1/checks as {"kind": "url", "value": "<GitHub link to the skill>"} or {"kind": "paste", "value": "<SKILL.md text>"} and read the event stream; the check's id comes first and its result page is https://skillbill.sh/r/<id>. No sign-in is needed to check a skill. Any page on this site answers in Markdown when the request's Accept header prefers text/markdown.

## Docs

- [SkillBill docs: API and agent guide](https://skillbill.sh/docs): when to use it, when not to, and how to call the API
- [Methodology](https://skillbill.sh/research/methodology): how a test is run and graded

## Pages

- [Home](https://skillbill.sh/): cut what your agent's skills cost
- [Check a skill](https://skillbill.sh/check): paste, upload or link a skill
- [The list](https://skillbill.sh/skills): measured results for published skills
- [About](https://skillbill.sh/about): who makes SkillBill
- [Contact](https://skillbill.sh/contact)

## Optional

- [Research](https://skillbill.sh/research): the studies behind the method
- [Privacy](https://skillbill.sh/privacy)
- [Terms](https://skillbill.sh/terms)
- [Sitemap](https://skillbill.sh/sitemap.xml)