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/lithic-webhooksnpx skills add hookdeck/webhook-skills --skill lithic-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/lithic-webhooks)<a href="https://agentmods.dev/skills/hookdeck/webhook-skills/lithic-webhooks"><img src="https://agentmods.dev/badge/skills/hookdeck/webhook-skills/lithic-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 | $0.00054 | $0.01777 |
| Opus 5 | $0.00027 | $0.00889 |
| Sonnet 5 | $0.00011 | $0.00355 |
| Haiku 4.5 | $0.00005 | $0.00178 |
Grade A, and why
lithic-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 yesterday.
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.
Lithic Webhooks
Lithic delivers events (card issuing, transactions, disputes, money movement) to
your endpoint as webhooks. They implement the Standard Webhooks
spec (powered by Svix), so verification is HMAC-SHA256 over
{webhook-id}.{webhook-timestamp}.{rawBody} with a per-subscription signing
secret.
When to Use This Skill
- How do I receive Lithic webhooks?
- How do I verify Lithic webhook signatures?
- How do I handle
card_transaction.updatedorpayment_transaction.createdevents? - Why is my Lithic webhook signature verification failing?
- How do I configure a Lithic event subscription and signing secret?
Signature at a Glance
| Property | Value |
|---|---|
| Headers | webhook-id, webhook-timestamp, webhook-signature (Svix also sends svix-* aliases) |
| Algorithm | HMAC-SHA256, base64-encoded |
| Signed content | {webhook-id}.{webhook-timestamp}.{rawBody} |
| Secret | Per-subscription, prefixed whsec_ (base64-decode the part after the prefix) |
| Signature header format | Space-delimited list of v1,<base64sig> |
| Timestamp tolerance | ~5 minutes (reject outside the window to block replays) |
Verification (core)
The official Lithic SDKs verify the signature and parse the event in a single
call — webhooks.unwrap(rawBody, headers, secret). It enforces the timestamp
tolerance and throws when verification fails. Always pass the raw request body.
Node (Express / Next.js):
const Lithic = require('lithic');
const lithic = new Lithic({ apiKey: process.env.LITHIC_API_KEY });
// rawBody: string from express.raw() or await request.text()
// headers: req.headers (Express) or Object.fromEntries(request.headers) (Next.js)
try {
const event = lithic.webhooks.unwrap(rawBody, headers, process.env.LITHIC_WEBHOOK_SECRET);
// event.event_type -> "card.created", "payment_transaction.created", ...
} catch (err) {
// invalid signature or stale timestamp -> respond 400
}
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 394 B
- examples/express/package.json 394 B
- examples/express/README.md 1.1 KB
- examples/express/src/index.js 3.7 KB runs code
- examples/express/test/webhook.test.js 4.5 KB runs code
- examples/fastapi/.env.example 394 B
- examples/fastapi/main.py 3.1 KB runs code
- examples/fastapi/README.md 1.4 KB
- examples/fastapi/requirements.txt 122 B
- examples/fastapi/test_webhook.py 4.1 KB runs code
- examples/nextjs/.env.example 394 B
- examples/nextjs/app/webhooks/lithic/route.ts 3.0 KB runs code
- examples/nextjs/package.json 506 B
- examples/nextjs/README.md 1.1 KB
- examples/nextjs/test/webhook.test.ts 4.9 KB runs code
- examples/nextjs/vitest.config.ts 121 B runs code
- references/overview.md 4.4 KB
- references/setup.md 2.8 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.
- yesterday First seen · 153 lines · 54 tokens per session scan A 7b833ee795e4
lithic-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (84 stars, last pushed yesterday), licensed MIT. It adds 54 tokens to every session and 1,777 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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