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 aomi-labs/skills --skill x402git clone --depth 1 https://github.com/aomi-labs/skillsWrote 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/aomi-labs/skills/x402)<a href="https://agentmods.dev/skills/aomi-labs/skills/x402"><img src="https://agentmods.dev/badge/skills/aomi-labs/skills/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/aomi-labs/skills/x402"><img src="https://agentmods.dev/badge/skills/aomi-labs/skills/x402.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 8 findings, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Data Exfiltration · line 257 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 288 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 289 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 316 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 322 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 31 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 183 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 351 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
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 | $0.00084 | $0.05502 |
| Opus 5 | $0.00042 | $0.02751 |
| Sonnet 5 | $0.00017 | $0.01100 |
| Haiku 4.5 | $0.00008 | $0.00550 |
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 11d 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 — 601 lines — stays where its author put it; the contents beside it link to each section on GitHub.
x402
x402 is an open payment protocol that revives the HTTP 402 "Payment Required" status code to enable instant stablecoin payments directly over HTTP. It uses a three-actor model — Client (buyer), Resource Server (seller), and Facilitator (settlement) — to let any HTTP endpoint accept payment without API keys, sessions, or accounts. The protocol is built on EIP-3009 transferWithAuthorization for gasless USDC transfers, meaning clients sign an off-chain authorization and the facilitator broadcasts the on-chain settlement.
Package ecosystem:
- Server (TypeScript):
@x402/express,@x402/hono,@x402/next - Client (TypeScript):
@x402/fetch,@x402/axios - Client (Python):
pip install x402 - Client (Go):
go get github.com/coinbase/x402/go - Core:
@x402/core,@x402/evm,@x402/svm
CDP Facilitator endpoint: https://api.cdp.coinbase.com/platform/v2/x402
What You Probably Got Wrong
LLMs have stale training data. These are the most common mistakes.
-
"x402 requires API keys or OAuth" -- There are no API keys. Payment IS authentication. The client signs a USDC transfer authorization, includes it in the
X-PAYMENTheader, and the server verifies it. If the signature and balance check pass, the request is authorized. No accounts, no sessions, no bearer tokens. -
"x402 only works on Base" -- The protocol supports any EVM chain where USDC implements EIP-3009 (Base, Ethereum, Arbitrum, Optimism, Polygon) and Solana. Network identifiers use CAIP-2 format:
eip155:8453for Base mainnet,eip155:1for Ethereum,solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdpfor Solana mainnet. -
"Nonces are sequential counters" -- x402 nonces are random 32-byte values (
bytes32), not incrementing integers. Each authorization generates a fresh random nonce. The ERC-3009 contract tracks used nonces on-chain to prevent replay. Using sequential nonces or reusing a nonce will cause settlement to revert. -
"The client pays gas" -- The client never submits an on-chain transaction. The client signs an off-chain EIP-712 authorization. The facilitator broadcasts the
transferWithAuthorizationcall and pays gas. CDP's hosted facilitator absorbs gas costs on Base mainnet for free-tier usage (1,000 tx/month).
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.
- 11d ago First seen · 601 lines · 84 tokens per session scan A 9fe12fe56184
x402 is a skill published in the GitHub repository aomi-labs/skills (7 stars, last pushed today), licensed MIT. It adds 84 tokens to every session and 5,502 once invoked, about $0.0004 per session on Opus 5. 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 2026-08-31.
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