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/mailchimp-webhooksnpx skills add hookdeck/webhook-skills --skill mailchimp-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/mailchimp-webhooks)<a href="https://agentmods.dev/skills/hookdeck/webhook-skills/mailchimp-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/mailchimp-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 5.1 | $0.00058 | $0.01673 |
| Opus 5 | $0.00029 | $0.00837 |
| Sonnet 5 | $0.00012 | $0.00335 |
| Haiku 4.5 | $0.00006 | $0.00167 |
Grade A, and why
mailchimp-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.
How it starts
The opening of the file, as written. The whole thing — 130 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mailchimp Webhooks
When to Use This Skill
- Setting up Mailchimp webhook handlers
- How do I respond to Mailchimp's webhook URL validation (the GET request)?
- How do I secure Mailchimp webhooks (they are not HMAC-signed)?
- Handling audience events: subscribe, unsubscribe, profile, upemail, cleaned, campaign
- Parsing Mailchimp's
application/x-www-form-urlencodedpayloads
Verification (core)
Mailchimp does NOT sign its webhooks — there is no HMAC and no signature header. You secure the endpoint two ways, both described in Mailchimp's sync audience data with webhooks guide:
- URL validation (GET): When you save a webhook, Mailchimp sends a
GETto the URL to confirm it is reachable. Respond200— do not require the secret on GET. - Shared secret (POST): Put an unguessable secret in the webhook URL's query string (e.g.
https://your.app/webhooks/mailchimp?secret=…) and compare it on everyPOSTwith a timing-safe comparison. Always serve the endpoint over HTTPS.
Payloads are application/x-www-form-urlencoded with a top-level type field and data[...] fields.
Node:
const crypto = require('crypto');
// Timing-safe compare of the ?secret= query param against your stored secret.
function verifyMailchimpSecret(provided, expected) {
if (!provided || !expected) return false;
const a = Buffer.from(provided);
const b = Buffer.from(expected);
if (a.length !== b.length) return false; // avoid throw on length mismatch
return crypto.timingSafeEqual(a, b);
}
Python:
import hmac
# Timing-safe compare of the ?secret= query param against your stored secret.
def verify_mailchimp_secret(provided: str, expected: str) -> bool:
if not provided or not expected:
return False
return hmac.compare_digest(provided, expected)
For complete handlers with GET validation, form parsing, event dispatch, and tests, see:
What ships with it
19 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 411 B
- examples/express/package.json 412 B
- examples/express/README.md 1.5 KB
- examples/express/src/index.js 4.4 KB runs code
- examples/express/test/webhook.test.js 5.3 KB runs code
- examples/fastapi/.env.example 411 B
- examples/fastapi/main.py 4.0 KB runs code
- examples/fastapi/README.md 1.6 KB
- examples/fastapi/requirements.txt 106 B
- examples/fastapi/test_webhook.py 5.2 KB runs code
- examples/nextjs/.env.example 363 B
- examples/nextjs/app/webhooks/mailchimp/route.ts 4.0 KB runs code
- examples/nextjs/package.json 534 B
- examples/nextjs/README.md 1.6 KB
- examples/nextjs/test/webhook.test.ts 5.3 KB runs code
- examples/nextjs/vitest.config.ts 140 B runs code
- references/overview.md 3.3 KB
- references/setup.md 2.5 KB
- references/verification.md 4.5 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 · 130 lines · 58 tokens per session scan A 063292e02171
mailchimp-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (84 stars, last pushed 2d ago), licensed MIT. It adds 58 tokens to every session and 1,673 once invoked, about $0.0003 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 2026-09-03.
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