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 hookdeck/webhook-skills --skill volume-webhooksgit clone --depth 1 https://github.com/hookdeck/webhook-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/hookdeck/webhook-skills/volume-webhooks)<a href="https://agentmods.dev/skills/hookdeck/webhook-skills/volume-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/volume-webhooks/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/hookdeck/webhook-skills/volume-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/volume-webhooks.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 | $0.00073 | $0.01979 |
| Opus 5.5 | $0.00029 | $0.00792 |
| Sonnet 5.5 | $0.00015 | $0.00396 |
| Haiku 4.5 | $0.00007 | $0.00198 |
Grade A, and why
volume-webhooks 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 8d 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 — 153 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Volume Webhooks
Volume is a UK open banking (pay-by-bank) payments
provider (API host volumepay.io). When a payment reaches a final status,
Volume sends an HTTP PUT webhook to the URL in your application
configuration. Each webhook is signed with Volume's RSA private key. You
verify it with Volume's public key. There is no shared secret, so an
HMAC check is always wrong here.
When to Use This Skill
- How do I receive Volume payment webhooks?
- How do I verify the Volume
Authorization: SHA256withRSA ...header? - Where do I get Volume's webhook public key (sandbox vs live)?
- How do I handle
COMPLETED,SETTLEDandFAILEDpayment webhooks? - Why is my Volume webhook signature verification failing?
Verification (core)
| Header | Authorization: SHA256withRSA <signature> |
| Algorithm | RSA PKCS#1 v1.5 + SHA-256 (Java SHA256withRSA), not PSS |
| Signature encoding | Standard base64 (not base64url, not hex) |
| Signed content | The raw request body bytes. No timestamp, no nonce |
| Public key | https://api.sandbox.volumepay.io/.well-known/signature/pem (sandbox)https://api.volumepay.io/.well-known/signature/pem (live) |
The key URL returns a bare base64 SPKI body without the
-----BEGIN/END PUBLIC KEY----- lines. Decode it as DER, or wrap it in PEM armour.
const crypto = require('crypto');
// pemBody: text from the .well-known/signature/pem URL (cache it, ~1 hour)
function verifyVolume(rawBody, authorization, pemBody) {
const key = crypto.createPublicKey({
key: Buffer.from(pemBody.trim(), 'base64'), format: 'der', type: 'spki',
});
const [scheme, signature] = (authorization || '').trim().split(/\s+/);
if (scheme !== 'SHA256withRSA' || !/^[A-Za-z0-9+/]+={0,2}$/.test(signature || '')) {
return false;
}
// RSA PKCS#1 v1.5 is Node's default padding for RSA keys
return crypto.verify('sha256', rawBody, key, Buffer.from(signature, 'base64'));
}
What ships with it
21 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.
- examples/express/.env.example 534 B
- examples/express/package.json 497 B
- examples/express/README.md 2.9 KB
- examples/express/src/index.js 7.6 KB runs code
- examples/express/test/webhook.test.js 14 KB runs code
- examples/fastapi/.env.example 534 B
- examples/fastapi/main.py 7.8 KB runs code
- examples/fastapi/README.md 3.0 KB
- examples/fastapi/requirements.txt 123 B
- examples/fastapi/test_webhook.py 14 KB runs code
- examples/nextjs/.env.example 534 B
- examples/nextjs/app/webhooks/volume/route.ts 2.8 KB runs code
- examples/nextjs/lib/volume.ts 5.2 KB runs code
- examples/nextjs/package.json 594 B
- examples/nextjs/README.md 2.9 KB
- examples/nextjs/test/webhook.test.ts 15 KB runs code
- examples/nextjs/tsconfig.json 563 B
- examples/nextjs/vitest.config.ts 157 B runs code
- references/overview.md 4.0 KB
- references/setup.md 3.0 KB
- references/verification.md 6.0 KB
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.
- 8d ago First seen · 153 lines · 73 tokens per session scan A d47d83e22e0a
volume-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (92 stars, last pushed yesterday), licensed MIT. It adds 73 tokens to every session and 1,979 once invoked, about $0.0003 per session on Opus 5.5. 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 2026-10-09.
Other skills, from other repositories
local-ai-agents
Build local-first AI agents that run entirely on a developer workstation with Microsoft Foundry Local and Qwen function-calling models. Covers Small Language Models (SLMs), the OpenAI-compatible local endpoint, sandboxed local tools, local RAG with Chroma, local MCP servers, hybrid cloud/local routing, and the…
systematic-debugging
Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.
next-cache-components-adoption
Turn on Cache Components in a Next.js app and resolve the blocking routes it surfaces. Use when the user wants to enable, adopt, or migrate to Cache Components, flip the cacheComponents flag, work through a flood of blocking-prerender / instant validation errors, run the cache-components-instant-false codemod, or…
chat-pet-sprite-creation
Use when creating or changing VS Code chat pet sprite art, sprite sheets, state animations, eye treatments, Stable/Insiders variants, or pet transitions under src/vs/workbench/contrib/chat/browser/widget/media/chatPet.
cpu-profile-analysis
Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…
insight-error-page
Write or audit an insight-kind error page for the Next.js dev overlay. Use when creating a new errors/ .mdx page, auditing an existing one, or checking that a page matches the framework fix cards. Covers page structure, title alignment, FixCard cards with Copy prompt button, code snippets, terminology verification…