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/facebook-webhooksnpx skills add hookdeck/webhook-skills --skill facebook-webhooksgit clone --depth 1 https://github.com/hookdeck/webhook-skillsWhat 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 | $0.00061 | $0.02214 |
| Opus 5 | $0.00030 | $0.01107 |
| Sonnet 5 | $0.00012 | $0.00443 |
| Haiku 4.5 | $0.00006 | $0.00221 |
Grade A, and why
facebook-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 3d 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 — 193 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Facebook Webhooks
Facebook webhooks are delivered through the Meta Graph API and are shared by Facebook Pages, Instagram, Messenger, WhatsApp, and other Meta products. They do not follow the Standard Webhooks spec.
Using WhatsApp? The WhatsApp Business Platform shares this exact Meta mechanism but has its own events, payloads, and setup — use the dedicated whatsapp-webhooks skill. This skill covers Facebook Pages, Instagram, and Messenger. The shared handshake +
X-Hub-Signature-256algorithm is documented once, canonically, in references/verification.md.
When to Use This Skill
- How do I receive Facebook (Meta Graph API) webhooks?
- How do I complete the Facebook GET verification handshake (hub.challenge)?
- How do I verify Facebook webhook signatures with X-Hub-Signature-256?
- Why is my Facebook webhook signature verification failing?
- How do I handle Page
feed,mention, Instagramcomments, or Messengermessagesevents?
Two Requests, Two Jobs
Facebook uses one endpoint for two different HTTP methods:
GET— verification handshake (one-time, on registration). Meta sendshub.mode=subscribe,hub.verify_token, andhub.challengeas query params. Ifhub.verify_tokenmatches the Verify Token you set in the App Dashboard, echo backhub.challengeas a200plain-text response.POST— event delivery. Meta sends a JSON body{ object, entry[] }and signs it withX-Hub-Signature-256.
Verification (core)
Meta signs the raw request body with HMAC-SHA256 keyed on your App
Secret and sends the digest in X-Hub-Signature-256 as sha256=<hex>. Verify
over the raw bytes before JSON parsing — Meta signs an escaped-unicode form
of the payload, so a re-serialized JSON string will not match. (The legacy
X-Hub-Signature header carries SHA-1 — prefer the SHA-256 header.)
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 391 B
- examples/express/package.json 389 B
- examples/express/README.md 1.1 KB
- examples/express/src/index.js 4.8 KB runs code
- examples/express/test/webhook.test.js 6.8 KB runs code
- examples/fastapi/.env.example 391 B
- examples/fastapi/main.py 4.2 KB runs code
- examples/fastapi/README.md 1.2 KB
- examples/fastapi/requirements.txt 82 B
- examples/fastapi/test_webhook.py 7.0 KB runs code
- examples/nextjs/.env.example 391 B
- examples/nextjs/app/webhooks/facebook/route.ts 4.1 KB runs code
- examples/nextjs/package.json 501 B
- examples/nextjs/README.md 1.2 KB
- examples/nextjs/test/webhook.test.ts 4.3 KB runs code
- examples/nextjs/vitest.config.ts 140 B runs code
- references/overview.md 3.8 KB
- references/setup.md 3.5 KB
- references/verification.md 4.7 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.
- 3d ago First seen · 193 lines · 61 tokens per session scan A 14f4c9bf8158
facebook-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (84 stars, last pushed 6d ago), licensed MIT. It adds 61 tokens to every session and 2,214 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 2026-08-30.
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