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/alchemy-webhooksnpx skills add hookdeck/webhook-skills --skill alchemy-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 | $0.00064 | $0.01456 |
| Opus 5 | $0.00032 | $0.00728 |
| Sonnet 5 | $0.00013 | $0.00291 |
| Haiku 4.5 | $0.00006 | $0.00146 |
Grade A, and why
alchemy-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 — 122 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Alchemy Webhooks
When to Use This Skill
- How do I receive Alchemy webhooks?
- How do I verify Alchemy webhook signatures (the
X-Alchemy-Signatureheader)? - How do I handle ADDRESS_ACTIVITY, MINED_TRANSACTION, or NFT_ACTIVITY events?
- Why is my Alchemy webhook signature verification failing?
- How do I set up Alchemy Notify webhooks for onchain activity?
Verification (core)
Alchemy signs every webhook with HMAC-SHA256 over the raw request body, hex-encoded, in the
X-Alchemy-Signature header. There is no sha256= prefix and no timestamp — just the hex digest.
The key is the per-webhook signing key (copied from the top-right of that webhook's detail page in
the Notify dashboard, or fetched via the Notify API), not your app's Auth Token.
The alchemy-sdk npm package manages webhook CRUD but does not verify signatures — implement HMAC
yourself. Always compute the HMAC over the raw body; a re-serialized JSON body will not match.
const crypto = require('crypto');
function verifyAlchemySignature(rawBody, signature, signingKey) {
if (!signature) return false;
const digest = crypto
.createHmac('sha256', signingKey)
.update(rawBody, 'utf8') // rawBody: exact bytes/string received, never re-stringified JSON
.digest('hex');
try {
return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(digest));
} catch {
return false; // length mismatch = invalid
}
}
For complete handlers with route wiring, event dispatch, and tests, see:
Common Event Types
The webhook type field identifies the event. Alchemy webhooks are scoped per chain/network.
| Type | Triggered When |
|---|---|
ADDRESS_ACTIVITY |
ETH/ERC-20/ERC-721/ERC-1155 transfers involving tracked addresses |
MINED_TRANSACTION |
A tracked transaction is mined into a block |
DROPPED_TRANSACTION |
A tracked transaction is dropped from the mempool |
NFT_ACTIVITY |
ERC-721/ERC-1155 transfers for tracked NFT contracts |
NFT_METADATA_UPDATE |
Metadata for a tracked NFT is refreshed |
GRAPHQL |
A Custom Webhook GraphQL query matches new onchain data |
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 218 B
- examples/express/package.json 377 B
- examples/express/README.md 1.1 KB
- examples/express/src/index.js 4.3 KB runs code
- examples/express/test/webhook.test.js 4.8 KB runs code
- examples/fastapi/.env.example 149 B
- examples/fastapi/main.py 3.8 KB runs code
- examples/fastapi/README.md 1.4 KB
- examples/fastapi/requirements.txt 82 B
- examples/fastapi/test_webhook.py 5.7 KB runs code
- examples/nextjs/.env.example 149 B
- examples/nextjs/app/webhooks/alchemy/route.ts 3.5 KB runs code
- examples/nextjs/package.json 489 B
- examples/nextjs/README.md 1.1 KB
- examples/nextjs/test/webhook.test.ts 3.3 KB runs code
- examples/nextjs/vitest.config.ts 140 B runs code
- references/overview.md 3.8 KB
- references/setup.md 3.2 KB
- references/verification.md 4.8 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 · 122 lines · 64 tokens per session scan A c6dc52c29b54
alchemy-webhooks is a skill published in the GitHub repository hookdeck/webhook-skills (84 stars, last pushed 6d ago), licensed MIT. It adds 64 tokens to every session and 1,456 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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