Tanod MCP server

utilpeek: sign or verify an HMAC (webhook signatures)

hmac_sign_verify

Read-onlyIdempotent

Sign or verify HMACs with a shared key for webhook and API payloads, including GitHub, Stripe, and Slack signatures, to check authenticity and integrity.

Instructions

utilpeek: Sign or verify an HMAC, including GitHub, Stripe and Slack webhook signatures. For plain digests use hash_text; for JWTs use verify_jwt. Returns the HMAC of a message under a shared key (sign), or whether a signature matches it in constant time (verify); handles GitHub (sha256= prefix accepted), Stripe v1 (of {t}.{raw body}) and Slack v0 (of v0:{timestamp}:{raw body}) webhook signatures. Input: mode, message, key, optional key_encoding, algorithm, output and, for verify, signature. Malformed hex or base64, a sha*= prefix naming another algorithm, or verify without a signature is a 422 (not charged). Other prefixes (v0=, v1=) are not stripped. sha1 is for legacy webhooks only. The key and message are never echoed. Typically under 0.1 s. Price: USD 0.001. Free: 10 utilpeek calls per IP per UTC day. The submitted text is never logged or stored. Docs: https://tanod.dev/learn/verify-webhook-signature-hmac-api.html

Input Schema

TableJSON Schema

Name	Required	Description	Default
`key`	Yes	The shared secret (at most 1 KiB), read as `key_encoding`. Never echoed or logged.
`mode`	Yes	sign (compute the HMAC) or verify (check `signature`).
`output`	No	Signature encoding: hex (default) or base64.	hex
`message`	Yes	The signed payload exactly as received (e.g. the raw webhook body), as text; at most 64 KiB as UTF-8.
`algorithm`	No	sha256 (default), sha512, or sha1 (legacy webhooks only).	sha256
`signature`	No	verify only: the signature to check, in `output` encoding. A `sha256=` style prefix (GitHub's X-Hub-Signature-256) is stripped when it names `algorithm`.
`key_encoding`	No	utf8 (default), hex or base64 (standard alphabet).	utf8

Output Schema

TableJSON Schema

Name	Required	Description
`error`	No	Only on an error result: an object {code, message}, or the reason string of an x402 PaymentRequired object.
`valid`	No
`output`	No
`algorithm`	No
`signature`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.0Oct 15, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Adds substantial behavior beyond the annotations: verify is a constant-time comparison, malformed hex/base64 or a mismatched `sha*=` prefix or verify-without-signature returns 422 and is not charged, non-`sha*=` prefixes (`v0=`, `v1=`) are deliberately not stripped, and key/message are never echoed or logged. Annotations already cover the safe-read/idempotent profile, and this text layers on the operational edge cases an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose then routing then mechanics, and nearly every sentence carries distinct information (prefix rules, 422 semantics, timing, pricing). It is dense and long, and the price/quota/docs sentences sit awkwardly mid-paragraph, but there is little true filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 7-param tool with an output schema and full annotation coverage, the description supplies everything else needed: sibling routing, provider-specific signature formats, error behavior, size/timing expectations, and data-handling guarantees. Nothing an agent needs to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3; the description goes beyond it by explaining how `signature` interacts with `algorithm` (the `sha256=` prefix is only stripped when it names the active algorithm) and by framing `message` as 'the signed payload exactly as received (e.g. the raw webhook body)', which is meaningful for signature correctness. It does not, however, re-explain `key_encoding` or `output` beyond what the schema already says.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource pairing ('Sign or verify an HMAC') and immediately scopes it with the concrete use case (GitHub, Stripe, Slack webhook signatures). It explicitly names the siblings it is not (hash_text for plain digests, verify_jwt for JWTs), so an agent can disambiguate without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit when-to-use and when-not-to-use routing: 'For plain digests use hash_text; for JWTs use verify_jwt', plus per-provider guidance (GitHub `sha256=` prefix, Stripe `v1` over `{t}.{raw body}`, Slack `v0` over `v0:{timestamp}:{raw body}`). It also flags sha1 as 'legacy webhooks only', a real selection constraint.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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