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 agentmods add skills/hookdeck/webhook-skills/polar-webhooksnpx skills add hookdeck/webhook-skills --skill polar-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/polar-webhooks)<a href="https://agentmods.dev/skills/hookdeck/webhook-skills/polar-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/polar-webhooks.svg" alt="Measured on agentmods" 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 | $0.00046 | $0.01564 |
| Opus 5 | $0.00023 | $0.00782 |
| Sonnet 5 | $0.00009 | $0.00313 |
| Haiku 4.5 | $0.00005 | $0.00156 |
Grade A, and why
polar-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 2d 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.
This is a copy
81% identical to adyen-webhooks — 164 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 137 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Polar Webhooks
When to Use This Skill
- How do I receive Polar webhooks?
- How do I verify Polar webhook signatures?
- How do I handle
order.paid,subscription.created, orcheckout.updatedevents? - Why is my Polar webhook signature verification failing?
- Setting up a Polar webhook endpoint in organization settings
Verification (core)
Polar follows the Standard Webhooks spec. Each request
carries three headers — webhook-id, webhook-timestamp, and webhook-signature — and the
signature is an HMAC-SHA256, base64-encoded, over {webhook-id}.{webhook-timestamp}.{body}.
Always verify against the raw request body — don't JSON.parse first.
Use Polar's official SDK helpers, which parse and verify in one call:
Node (@polar-sh/sdk):
const { validateEvent, WebhookVerificationError } = require('@polar-sh/sdk/webhooks');
try {
// rawBody: Buffer/string of the raw HTTP body; headers: the request headers object
const event = validateEvent(rawBody, headers, process.env.POLAR_WEBHOOK_SECRET);
// event.type -> e.g. "order.paid"; event.data -> the resource
} catch (err) {
if (err instanceof WebhookVerificationError) {
// invalid signature -> respond 400/403
}
}
Python (polar-sdk):
from polar_sdk.webhooks import validate_event, WebhookVerificationError
try:
event = validate_event(body=raw_body, headers=request.headers,
secret=os.environ["POLAR_WEBHOOK_SECRET"])
except WebhookVerificationError:
... # invalid signature -> respond 400/403
Secret gotcha: The Standard Webhooks spec expects the secret to be base64-encoded before signing. The Polar SDKs base64-encode your dashboard secret for you, so pass the secret as-is. For a manual verifier, base64-encode the secret first (see references/verification.md). Polar secrets are user-set or randomly generated — they are not
whsec_-prefixed.
What ships with it
22 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 213 B
- examples/express/package.json 398 B
- examples/express/README.md 1.6 KB
- examples/express/src/index.js 3.8 KB runs code
- examples/express/test/fixtures/order-paid.json 3.6 KB
- examples/express/test/webhook.test.js 4.6 KB runs code
- examples/fastapi/.env.example 213 B
- examples/fastapi/fixtures/order-paid.json 3.6 KB
- examples/fastapi/main.py 3.3 KB runs code
- examples/fastapi/README.md 2.1 KB
- examples/fastapi/requirements.txt 100 B
- examples/fastapi/test_webhook.py 4.1 KB runs code
- examples/nextjs/.env.example 213 B
- examples/nextjs/app/webhooks/polar/route.ts 3.3 KB runs code
- examples/nextjs/package.json 510 B
- examples/nextjs/README.md 1.9 KB
- examples/nextjs/test/fixtures/order-paid.json 3.6 KB
- examples/nextjs/test/webhook.test.ts 3.5 KB runs code
- examples/nextjs/vitest.config.ts 140 B runs code
- references/overview.md 3.2 KB
- references/setup.md 2.4 KB
- references/verification.md 5.0 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.
- 2d ago First seen · 137 lines · 46 tokens per session scan A 656268ccb07c
polar-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (84 stars, last pushed yesterday), licensed MIT. It adds 46 tokens to every session and 1,564 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 81% identical to adyen-webhooks, differing in 164 lines, and is treated as a copy.
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