x402-before-you-pay

x402-before-you-pay is a skill for Claude Code, Codex from seancrecord/scvd-general-store-repo. It costs 90 tokens per session (808 once invoked), scanned A, original, MIT.

A safety check for paid x402 web endpoints, which are web addresses that request payment before serving a response. It reads the payment terms and tests what the payment client would do before signing anything.

In plain words
What is it for?
Use it before calling a paid x402 URL, when a payment request looks wrong, or when a payment appears not to have completed.
Why use it?
It helps prevent an agent from paying the wrong recipient, asset, network, or amount, and distinguishes a safe decision from one that cannot be verified.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: reads .claude/ paths; mentions Claude Code; mentions Cursor.

Good fit Use it before calling a paid x402 URL, when a payment request looks wrong, or when a payment appears not to have completed.

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Install with agentmods
npx agentmods add skills/seancrecord/scvd-general-store-repo/claude-code
Install

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.

Any agent
npx skills add seancrecord/scvd-general-store-repo --skill claude-code
Clone the repo
git clone --depth 1 https://github.com/seancrecord/scvd-general-store-repo

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for x402-before-you-pay

README.md
[![agentmods](https://agentmods.dev/badge/skills/seancrecord/scvd-general-store-repo/claude-code/github.svg)](https://agentmods.dev/skills/seancrecord/scvd-general-store-repo/claude-code)
Your own site
<a href="https://agentmods.dev/skills/seancrecord/scvd-general-store-repo/claude-code"><img src="https://agentmods.dev/badge/skills/seancrecord/scvd-general-store-repo/claude-code/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.

agentmods 80×15 button for x402-before-you-pay

Your own site · 80×15
<a href="https://agentmods.dev/skills/seancrecord/scvd-general-store-repo/claude-code"><img src="https://agentmods.dev/badge/skills/seancrecord/scvd-general-store-repo/claude-code.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 90 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 808 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00090 $0.00808
Opus 5 $0.00045 $0.00404
Sonnet 5 $0.00018 $0.00162
Haiku 4.5 $0.00009 $0.00081

Measured 5d ago against content hash 6c75c43ebf7e, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

x402-before-you-pay 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 5d 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.

examples/claude-code/SKILL.md · 42 lines

How it starts

The opening of the file, as written. The whole thing — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.

x402: before you pay

A skill for Claude Code (copy this directory to .claude/skills/x402-before-you-pay/) and, with the frontmatter removed, a Cursor rule (x402-before-you-pay.mdc beside it).

When to use it

  • Code is about to call an x402 URL with a payment client (@x402/fetch, x402-axios, a wallet-backed agent).
  • A 402 looks wrong, or a payment "never went through" and the operator's logs show a clean 402 followed by silence.
  • A signed receipt or offer needs checking without trusting the party that produced it.

The walk, in order

  1. Read the door's 402 yourself. GET the URL; decode the PAYMENT-REQUIRED header (base64 JSON). The accepts[] entries carry network, asset, payTo and amount (atomic units). Those are the terms you would sign.

  2. One POST to the free dry run. POST https://scvd.store/api/before-you-pay/v1 with {"url": "<the url>"}. The answer says whether a stock x402 client would sign (will_your_client_pay: would_sign / would_throw / cannot_simulate), which accept it would pick (your_client.chosen), and carries the free preflight whole as the_door (verdict: ready / not_ready / unreachable, every check and advisory named).

  3. Decide, and name why. The shared logic is examples/shared/decide.mjs (or decide.py); run it rather than re-deriving:

    node -e 'import("./examples/shared/decide.mjs").then(async m => console.log(JSON.stringify((await m.beforeYouPayWalk(process.argv[1], { policy: { allowed_networks: ["eip155:8453"], max_amount_usd: 1 } })).decision, null, 2)))' -- https://door.example/api/paid-answer
    

    Or with the CLI, for the door's shape alone: npx scvd-cli preflight https://door.example/api/paid-answer.

How to read the answer

  • unreachable is not a defect. Unknown is never a difference; the decision is cannot_tell.
  • not_ready names the failed checks; do_not_pay, and quote them.
  • would_throw means your own client refuses on your machine before any signature exists. The operator never learns you tried. do_not_pay, and quote throws_with.
  • A testnet-network advisory means a mainnet wallet signing this settles nowhere real. do_not_pay.
  • pay is a derivation from those readings plus your policy (allowed networks, allowed recipients, a cap). It is not a score and not proof of delivery: does_not_establish rides on every answer. Say so when you report it.

Read the full file on GitHub · 42 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

  1. 5d ago First seen · 42 lines · 90 tokens per session scan A 6c75c43ebf7e

Subscribe to this mod's changes

x402-before-you-pay is a skill published in the GitHub repository seancrecord/scvd-general-store-repo (3 stars, last pushed today), licensed MIT. It adds 90 tokens to every session and 808 once invoked, about $0.0005 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 2026-09-04.

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