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 checkout-com-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/checkout-com-webhooks)<a href="https://agentmods.dev/skills/hookdeck/webhook-skills/checkout-com-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/checkout-com-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/checkout-com-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/checkout-com-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 | $0.00147 | $0.04574 |
| Opus 5.5 | $0.00059 | $0.01830 |
| Sonnet 5.5 | $0.00029 | $0.00915 |
| Haiku 4.5 | $0.00015 | $0.00457 |
Grade A, and why
checkout-com-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 18d 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 — 325 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Checkout.com Webhooks
Checkout.com (checkout.com) is a global payments processor. It sends webhooks for payments, disputes, fraud, payouts, issuing and identity verification.
This skill targets the current ("NAS" / Workflows) platform — webhooks configured under Dashboard → Developers → Webhooks, or created as a
webhookaction onPOST https://{prefix}.api.checkout.com/workflows. See Legacy accounts if you are on the previous ("ABC") platform.Canonical docs: Receive webhooks and Configure your webhook server → Validate the payload.
Not Checkout Page (checkoutpage.com), not CheckoutJoy, not 2Checkout / Verifone, not Stripe Checkout, not Shopify checkout webhooks. 2Checkout (now Verifone) in particular is a different company with an entirely different INS/IPN scheme — none of this applies there.
When to Use This Skill
- How do I receive Checkout.com webhooks?
- How do I verify a Checkout.com webhook signature?
- Why is my
Cko-Signatureverification failing? - How do I handle
payment_approved,payment_capturedorpayment_declined? - How do I handle
dispute_receivedand the rest of the dispute lifecycle? - What is the
Authorizationheader Checkout.com sends on my webhooks? - Does Checkout.com send a handshake or challenge request?
- Why does
created_onsometimes not exist on a Checkout.com event?
Two Optional Mechanisms, One That Proves Integrity
Checkout.com configures two independent, optional verification mechanisms per webhook. Implement both; check whichever you have a value for.
| Cko-Signature — primary | Authorization — optional | |
|---|---|---|
| Header | Cko-Signature |
Authorization |
| What it is | HMAC-SHA256 of the raw body, hex (Base16) | The configured key sent verbatim |
| Proves | Sender identity and body integrity | Sender knows a shared secret. Nothing about the body. |
| Configured as | "signature key" (Dashboard) / actions[].signature.key (Workflows API) |
actions[].headers.Authorization |
| Env var here | CHECKOUT_WEBHOOK_SIGNATURE_KEY |
CHECKOUT_WEBHOOK_AUTHORIZATION_KEY |
What ships with it
20 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 982 B
- examples/express/package.json 519 B
- examples/express/README.md 3.8 KB
- examples/express/src/index.js 15 KB runs code
- examples/express/test/webhook.test.js 12 KB runs code
- examples/fastapi/.env.example 982 B
- examples/fastapi/main.py 16 KB runs code
- examples/fastapi/README.md 4.1 KB
- examples/fastapi/requirements.txt 82 B
- examples/fastapi/test_webhook.py 15 KB runs code
- examples/nextjs/.env.example 957 B
- examples/nextjs/app/webhooks/checkout-com/route.ts 15 KB runs code
- examples/nextjs/package.json 597 B
- examples/nextjs/README.md 4.3 KB
- examples/nextjs/test/webhook.test.ts 12 KB runs code
- examples/nextjs/vitest.config.ts 162 B runs code
- references/overview.md 8.9 KB
- references/setup.md 7.4 KB
- references/verification.md 12 KB
- TODO.md 1.3 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.
- 18d ago First seen · 325 lines · 147 tokens per session scan A 782f45047c40
checkout-com-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (92 stars, last pushed today), licensed MIT. It adds 147 tokens to every session and 4,574 once invoked, about $0.0006 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 2026-09-29.
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