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 OpenLinkSoftware/ai-agent-skills --skill x402-buyergit clone --depth 1 https://github.com/OpenLinkSoftware/ai-agent-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/openlinksoftware/ai-agent-skills/x402-buyer)<a href="https://agentmods.dev/skills/openlinksoftware/ai-agent-skills/x402-buyer"><img src="https://agentmods.dev/badge/skills/openlinksoftware/ai-agent-skills/x402-buyer/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/openlinksoftware/ai-agent-skills/x402-buyer"><img src="https://agentmods.dev/badge/skills/openlinksoftware/ai-agent-skills/x402-buyer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 7 findings, up to high
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 →
- high Tool Misuse · line 138 Tool parameters are crafted to achieve unintended or unsafe behavior. Parameter abuse can bypass intended safety checks (e.g. shell=True, --force, dangerous glob patterns).Fix: Validate all tool parameters against an allowlist. Reject dangerous parameter values (shell=True, --force, -rf /) and use safe defaults.
- high Tool Misuse · line 167 Tool parameters are crafted to achieve unintended or unsafe behavior. Parameter abuse can bypass intended safety checks (e.g. shell=True, --force, dangerous glob patterns).Fix: Validate all tool parameters against an allowlist. Reject dangerous parameter values (shell=True, --force, -rf /) and use safe defaults.
- high Privilege Escalation · line 343 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 361 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- medium Data Exfiltration · line 138 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 167 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 Excessive Agency · line 192 Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
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 | $0.00226 | $0.05418 |
| Opus 5 | $0.00113 | $0.02709 |
| Sonnet 5 | $0.00045 | $0.01084 |
| Haiku 4.5 | $0.00023 | $0.00542 |
Grade A, and why
x402-buyer scanned grade A with 1 finding 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 12d 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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
curl -sS -o /dev/null -D - -k "<target-url>" How it starts
The opening of the file, as written. The whole thing — 420 lines — stays where its author put it; the contents beside it link to each section on GitHub.
x402 Buyer Skill
Buyer-side client for the x402 payment protocol (v2). Given a URL, it performs the full challenge → sign → retry → settle loop and reports what the facilitator did.
When to Use
- "Pay for
{url}with x402" - "Fetch this 402-protected resource"
- "Run the x402 buyer against
{url}" - "Settle this 402 challenge" / "What does the facilitator say about
{url}?" - "Test OPL Shop's x402 support on DAV / SPARQL / OPAL"
- Any request naming x402,
PAYMENT-REQUIRED,PAYMENT-SIGNATURE,PAYMENT-RESPONSE, EIP-3009, or a Base Sepolia facilitator.
Not this skill: a 402 carrying a Stripe/MPP challenge rather than an
x402 PAYMENT-REQUIRED header — use mpp-stripe-client or acp-client.
If you are unsure which protocol a URL speaks, run the probe in
Step 1 before committing.
Prerequisites
Python 3, plus the buyer-side SDK stack:
python3 -m venv .venv && source .venv/bin/activate && pip install eth_account requests jsonschema "x402[requests,evm,extensions]"
jsonschema / the extensions extra is required even for a plain fetch —
the SDK validates any extension the server's challenge advertises (e.g.
eip2612GasSponsoring) before it will create a payment payload at all.
Missing it fails deep inside signing, after the challenge already decoded
successfully — see references/setup.md.
macOS: pip install keyring is optional — without it the script shells out
to /usr/bin/security for the same Keychain item.
Linux / Windows: pip install keyring is required for credential-store
access. There is no fallback binary on those platforms; without it, the key
resolver skips straight to the interactive prompt on every run. See
Cross-Platform Notes for the Linux caveat.
A funded buyer wallet private key. It is spent from, so it must hold
testnet USDC on whatever network the server's PAYMENT-REQUIRED accepts[]
advertises — Base Sepolia (eip155:84532) by default. Two testnet funding
paths:
What ships with it
8 files 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.
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.
- 12d ago First seen · 420 lines · 226 tokens per session scan A a9d1273433ca
x402-buyer is a skill published in the GitHub repository OpenLinkSoftware/ai-agent-skills (38 stars, last pushed today), licensed MIT. It adds 226 tokens to every session and 5,418 once invoked, about $0.0011 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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