AISKILLS402

x402 Seller: Payable and Listed

x402 Seller: Payable and Listed is a tested SKILL.md that 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; an agent buys it once for $0.10 over x402.

$0.10once · USDC on Base

Price as loaded on this page. The 402 response your agent receives is authoritative.

Tested 2026-09-30No code, no hidden instructionsv1.0.0 · 14.0 KB · perpetual license
How your agent buys itShare

Use it when

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.

Not for

Building a seller from scratch, guaranteeing a Bazaar listing, or proving live behaviour: it reads pasted 402 responses and symptoms only, never calls your endpoint.

Tested, honestly

Tested 2026-09-30 with a strong and a weak model.

Strong · Claude Sonnet (claude-sonnet-5-5, Claude Code alias "sonnet")
Named the planted defect in all 6 cases in every run (missing PAYMENT-REQUIRED header, missing extra, extensions placed inside accepts[0], test network plus x402.org facilitator, UTF-8 versus atob decoding, the 30-day delisting), also found a second defect where present, wrote the German case in German, and never promised a listing. Sometimes adds cautious extra remarks (a placeholder address, the missing bazaar block on a body that never claimed one).
Weak · Claude Haiku (claude-haiku-4-5-20251001, Claude Code alias "haiku")
Named the planted defect in 6 of 6 cases on the second run. On the first run it missed the missing extra field entirely and reported only a masked placeholder wallet address as the defect; a rule to tick every field and treat placeholders as redaction fixed that in the next run. Still breaks the no-code-block rule (shows a small JSON snippet), quotes the skill file back to the reader, and once used up to 9,000 tokens on one case. Weaker on the German case wording (verdict line not in the requested form). Slightly over-promises timing of a listing (says it should appear within minutes to hours).

Full test summary

What is in the file

  • Hard rules
  • What a correct seller looks like
  • The checklist, cheapest and most common first
  • Decision tree from the symptom
  • How to prove each repair
  • Output format
  • Examples of the judgement

Languages

Any language.

How to buy

Any x402 client works. Without a payment header the endpoint answers 402 and tells your agent what it costs. Sign it, repeat the request with PAYMENT-SIGNATURE, and the file comes back.

Agent (HTTP)

curl -i https://api.aiskills402.com/v1/skills/x402-seller/file

Agent (MCP)

Connect https://mcp.aiskills402.com/mcp, then use the free tools get_skill (card and payment requirements) and redownload_skill. The payment itself goes over HTTP.

I am a person

Honestly: you need an agent with a USDC wallet, or a small script, plus the x402-buyer skill. There is no card checkout yet. The steps are in the docs.

The file

Version
1.0.0
Payment
x402 · USDC · base
Updates
free, new versions included
Size
14.0 KB (14377 bytes)
SHA-256
d8a89eaa67757d8e10b3681cc7bb1fff380d3361fb79f8dd0843afbc24b1e613
Updated
2026-09-30

License

Perpetual, non-exclusive; use and modify for yourself incl. paid work; no resale or republishing. Holder: Georgi Kalchev, aiskills402.com. Full terms.

Versions

Current version 1.0.0, updated 2026-09-30. Whoever bought an earlier version gets new ones free through the same re-download token.

FAQ

What defects does it find?

In our test set it named the planted fault in every case: a missing payment-required header, a missing extra field, discovery data placed inside the wrong object, a test network paired with the wrong facilitator, a decoding mistake with non-ASCII text, and a listing dropped after 30 days without a settlement.

Will it get my API into the catalog?

No, and it says so. Listing depends on the catalog's own rules, which can change, and on a real settled payment. The skill finds what blocks a listing and how to prove each fix, but it never promises a listing or a timing.

Does it call my endpoint?

No. It reads the 402 response, headers and symptoms you paste and works through an ordered checklist. Anything that needs live behaviour, such as settlement history or edge settings, you have to check yourself, and the skill tells you which check.

Related skills

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Read this page as Markdown: /skills/x402-seller.md.