# AISkills402

Tested AI agent skill files (SKILL.md, Agent Skills format). An agent buys the FILE of a skill once, over the x402 protocol, in USDC on Base mainnet (eip155:8453), for cents. It keeps the file forever: free re-downloads and free new versions. No account, no API key.

## What is sold

The skill file itself. Not an API call, not a run: you pay once, you receive SKILL.md, and it is yours. Every skill is tested by us with a strong and a weak model, and each skill card says honestly where the weak one fails.

The till is open: the 402 answer carries the payment requirements.

## How to buy (HTTP)

1. `GET https://api.aiskills402.com/v1/skills/humanize/file` with no payment header.
2. The answer is 402 with a `PAYMENT-REQUIRED` header (base64 JSON, x402 v2). It holds the exact amount, asset, network and recipient.
3. Sign `accepts[0]` (scheme `exact`, USDC, Base) with an x402 client, for example `@x402/core` + `@x402/evm`.
4. Repeat the same GET with the signature in the `PAYMENT-SIGNATURE` header.
5. The answer is 200 JSON: `file.content` (the SKILL.md text), `sha256`, `receipt{tx,...}` and `redownload{token,url}`.

The price is $0.05. That is under the default $1 per-payment cap of @x402/core clients, so a default client signs without extra configuration.

If the 402 body says `selling: false` or "do not sign", the till is closed: do not sign.

## Keep it: re-download and versions

The token in `redownload.token` is shown ONCE, at purchase. Store it. `GET https://api.aiskills402.com/v1/purchases/{token}` returns the current file again, free. New versions of a skill you own are free through the same token.

## Install

Save the file as `~/.claude/skills/<slug>/SKILL.md` (all your projects) or `.claude/skills/<slug>/SKILL.md` inside one project.

## License

Perpetual, non-exclusive. Use and modify the file for yourself, including in paid work. No resale and no republishing. Holder: Georgi Kalchev, aiskills402.com. Full text: https://aiskills402.com/docs#license

## What you are charged

- Success: $0.05 once.
- The facilitator refuses the payment: nothing.
- Settlement outcome unknown: you still receive the file; we reconcile by hand.

## What we keep

Payer wallet, transaction hash, token hash. No customer text.

## Endpoints

- Catalog: GET https://api.aiskills402.com/v1/skills
- One skill card: GET https://api.aiskills402.com/v1/skills/{slug}
- Buy: GET https://api.aiskills402.com/v1/skills/{slug}/file (x402)
- Re-download: GET https://api.aiskills402.com/v1/purchases/{token}
- MCP server: https://mcp.aiskills402.com/mcp
  Free tools: search_skills, get_skill (card plus the payment requirements), redownload_skill({token}). Buying is over HTTP in this release; MCP does not pay.

Errors: skill_not_found, payment_in_progress, facilitator_unavailable, head_cannot_settle, not_selling, execution_retired (410 on the retired run endpoint).

## Writing & Rewriting

- [Humanize](https://aiskills402.com/skills/humanize.md): Rewrites AI-sounding prose so it reads like a person wrote it — in any language, without dropping facts. Use when asked to humanize a text, make it sound less AI-generated or less like ChatGPT, or clean machine phrasing out of an article, post, email, product description or page.; $0.05 once

## Editing & Proofreading

- [Proofread](https://aiskills402.com/skills/proofread.md): Proofreads a text with minimal intervention, in the language of the text. Fixes spelling, grammar, punctuation and obvious typos, keeps everything else, and returns the corrected text plus a short list of changes for review. Use when asked to proofread, correct, spell-check or fix the mistakes in a text without rewriting it.; $0.03 once

## Marketing & Copy

- [Cold Email](https://aiskills402.com/skills/cold-email.md): Writes a short, honest first outreach message to a stranger in business, in the recipient's language, with a subject line, one specific reason for writing and one small ask. Use when asked to write a cold email, a first outreach message, a sales or partnership introduction, or a prospecting note, in any language.; $0.03 once

## SEO & Content

- [SEO Meta Writer](https://aiskills402.com/skills/seo-meta.md): Writes the SEO title, meta description and (on request) the H1 heading for one web page, in the page's own language, inside hard character limits, matching what the searcher wants. Use when asked to write or rewrite a page title, meta description, SEO snippet or H1 for a page, product, service, article or landing page.; $0.03 once

## Research & Summaries

- [Faithful Summary](https://aiskills402.com/skills/summarize.md): Writes a faithful summary of a text in the text's own language, using only what the text says, with every number, name and date kept exactly and every qualifier kept. Use when asked to summarize, shorten, condense, give the gist or a TL;DR of an article, report, email, transcript, thread or document.; $0.03 once

## Code & Engineering

- [Code Review](https://aiskills402.com/skills/code-review.md): Reviews a code change (a diff or a changed file pasted as text) and reports real problems ranked by severity — correctness bugs, security holes, data loss, missing error handling, edge cases, resource leaks — each with location, reason and a concrete fix in words. Use when asked to review code, a diff or a pull request, check a change for bugs, or find security problems in a snippet.; $0.05 once

## Agents & Protocols

- [Pay Safely over x402](https://aiskills402.com/skills/x402-buyer.md): Decision rules for an AI agent that holds a wallet and receives an HTTP 402 payment request (x402 v2). Decides SIGN, REFUSE or ASK the human before any money moves, and says how to verify the delivery and retry without paying twice. Use when an agent is about to pay over x402, gets a 402 response, must check a seller's payment terms, or a paid request failed and it is unsure whether to pay again.; $0.03 once
- [x402 Seller: Payable and Listed](https://aiskills402.com/skills/x402-seller.md): Diagnoses why an HTTP API sold over x402 v2 cannot be paid by standard buyer agents or never appears in the Coinbase CDP Bazaar catalog, using an ordered checklist and a decision tree over the pasted 402 response, headers and symptoms. Names the exact field that is wrong or missing and how to prove the fix. Use when asked to check an x402 seller, fix an unpayable 402 endpoint, find out why a resource is not listed in Bazaar, or why a settled payment does not show up.; $0.10 once

## More formats

Every skill page above has a Markdown twin: the same sections as the web page (when to use it, honest test results, price, how to buy). All twins in one file: https://aiskills402.com/llms-full.txt. Atom feed of skills: https://aiskills402.com/skills/feed.xml

## Blog

- [Add an MCP server to Claude Code: what free tools expose](https://aiskills402.com/blog/add-mcp-server-claude-code.md): The current commands to connect a remote MCP server to Claude Code, then what a server's free tools should and should not offer, using our own four.
- ["paymentPayload is invalid": one dash broke a payment](https://aiskills402.com/blog/payment-payload-invalid-dash.md): Our first real x402 purchase on mainnet failed with a schema error caused by one em dash and a bare atob call. The cause, the fix, and how we proved it free.
- [Write a SKILL.md your agent uses, and test it first](https://aiskills402.com/blog/skill-md-write-and-test.md): What makes an agent pick up a SKILL.md, how to keep its rules checkable, and how to test it on a stronger and a weaker model, with a check that can fail.
- [Eight skills, two models: where the weaker one fails](https://aiskills402.com/blog/weak-model-eight-skills.md): We ran eight SKILL.md files on a strong and a weak model. Both mostly passed our checks; the weak one failed in ways checks cannot see, and used more tokens.
- [What an agent should check before signing an x402 payment](https://aiskills402.com/blog/when-should-agent-pay-402.md): The values an agent or its developer should compare before signing an x402 payment, which ones our own buyer script checks, and which it leaves out.
- [Not in the x402 Bazaar? Nine silent causes, in order](https://aiskills402.com/blog/x402-not-in-bazaar.md): Nine causes of a missing Bazaar listing that leave no error anywhere, cheapest to check first, each with a command that proves it and a control that can fail.

Atom feed of the blog: https://aiskills402.com/blog/feed.xml