Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add ChainGPT-org/chaingpt-claude-skill --skill x402git clone --depth 1 https://github.com/ChainGPT-org/chaingpt-claude-skillWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/chaingpt-org/chaingpt-claude-skill/x402)<a href="https://agentmods.dev/skills/chaingpt-org/chaingpt-claude-skill/x402"><img src="https://agentmods.dev/badge/skills/chaingpt-org/chaingpt-claude-skill/x402/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/chaingpt-org/chaingpt-claude-skill/x402"><img src="https://agentmods.dev/badge/skills/chaingpt-org/chaingpt-claude-skill/x402.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00000 | $0.00743 |
| Opus 5.5 | $0.00000 | $0.00297 |
| Sonnet 5.5 | $0.00000 | $0.00149 |
| Haiku 4.5 | $0.00000 | $0.00074 |
Grade A, and why
x402 scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 48 lines — stays where its author put it; the contents beside it link to each section on GitHub.
x402 Payments skill
x402 turns HTTP 402 Payment Required into a real payment rail for agents: a
server replies 402 with what it wants paid; the client signs an off-chain
authorization and retries with an X-PAYMENT header; a facilitator broadcasts
it. Settlement uses EIP-3009 transferWithAuthorization (e.g. USDC on Base) —
the facilitator can only broadcast the signed authorization, never alter the
amount or destination.
Custody-free: the plugin builds the EIP-712 the payer signs and assembles the header; it never holds a key.
Tools
| Tool | Purpose |
|---|---|
chaingpt_x402_decode |
Decode a 402 body or X-PAYMENT header into human terms (amount/token/recipient/expiry) before paying. |
chaingpt_x402_build_payment |
Build the UNSIGNED EIP-3009 typed data; pass a signature back to get the final X-PAYMENT header. |
chaingpt_x402_facilitator |
Call a facilitator: supported / verify / settle. |
chaingpt_x402_create_requirements |
Server side: generate the PaymentRequirements + 402 body to monetize your endpoint. |
chaingpt_x402_fetch |
The whole client loop in one tool: fetch a URL; on 402 it decodes the challenge and (given from) emits the unsigned typed data; re-call with xPaymentHeader to complete the paid request. |
Pay an endpoint (client flow)
Fast path — one tool drives the loop:
chaingpt_x402_fetch url=<resource> from=<payer>→ on 402 you get the decoded price/payee AND the unsigned EIP-3009 typed data.- Sign the typed data in the payer's wallet.
chaingpt_x402_build_payment from=<payer> requirements=<from step 1> signature=0x…→ theX-PAYMENTheader.chaingpt_x402_fetch url=<resource> xPaymentHeader=<header>→ the paid response.
Manual path (same primitives, finer control): _decode → _build_payment → sign → _build_payment +signature → retry yourself.
Monetize your endpoint (server flow)
chaingpt_x402_create_requirements network=base amount=0.01 payTo=<you> → serve
the returned JSON with HTTP 402. Verify/settle incoming payments via a
facilitator (chaingpt_x402_facilitator).
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 48 lines · 0 tokens per session scan A cc5a82488bd0
x402 is a skill published in the GitHub repository ChainGPT-org/chaingpt-claude-skill (7 stars, last pushed 1mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 743 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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