HMAC Signing Skill
The tool
HMAC combines a cryptographic hash function with a secret key to produce a signature that verifies both data integrity and authenticity. Essential for API authentication, webhook verification, and secure message signing.
Once your client is connected to the VerveKit MCP server, this appears in its tool list as HMACSigningSkill. It is read-only and open-world: it fetches, it never mutates anything on your side, so most clients will call it without asking you to confirm.
{
"name": "HMACSigningSkill",
"arguments": {
"message": "Hello World",
"secret": "my-secret-key"
}
}What that looks like in a conversation
You don't name the tool — the model picks it. Asking about Hello World in the terms this source covers is enough for it to reach for HMACSigningSkill on its own.
Connecting
One server URL covers every skill in the catalog, including this one. Authorization is OAuth — the client opens a browser once and there is no key to paste into a config file.
{
"mcpServers": {
"vervekit": {
"url": "https://api.vervekit.com/v1/mcp"
}
}
}https://api.vervekit.com/v1/mcpPer-client setup — Claude Desktop, Cursor, VS Code, ChatGPT — is on the MCP setup page.
Arguments
These are the properties on the tool's inputSchema, so a well-behaved client validates them before the call is made.
| Argument | Type | Example | Description |
|---|---|---|---|
messageRequired | string | Hello World | The message to sign |
secretRequired | string | my-secret-key | The secret key for HMAC generation |
algorithm | string | sha256 | Hash algorithm to use One of: sha256, sha384, sha512, sha1, md5. |
encoding | string | hex | Output encoding format One of: hex, base64. |
What the model gets back
The result carries a structuredContent object matching the tool's declared outputSchema, so a client can read fields without parsing prose. status is "ok" on success and error is null; a null field means the value wasn't available for that input, not that the call failed.
{
"status": "ok",
"error": null,
"data": {
"hmac": "2cd7c25025198d4458002ceb064ad37ccfbbe46650876d693f5e080bd954e449",
"algorithm": "sha256",
"encoding": "hex"
}
}Fields
| Field | Type | Example | Description |
|---|---|---|---|
hmac | string | 2cd7c25025198d4458002ceb064ad37ccfbbe46650876d693f5e080bd954e449 | Generated HMAC signature in specified encoding format |
algorithm | string | sha256 | Hash algorithm used for HMAC generation |
encoding | string | hex | Output encoding format applied to the signature |
Failure modes
Errors come back as tool errors with a sentence the model can act on, not a bare status code.
| Status | What it means |
|---|---|
400 / 422 | The arguments didn't validate. The message names the offending one. |
401 | The OAuth session is invalid or expired — reconnect the server. |
403 | Out of credits. Not a bad key — the month's allowance is spent. |
404 | This skill isn't part of VerveKit. Check the catalog. |
429 | Brief rate limit. Retrying after a moment succeeds. |
Other ways to use HMAC Signing Skill
Set up HMAC Signing Skill on VerveKit, or reach the same source a different way. Your VerveKit account and credits work on all of them — one key, one balance.
Frequently asked questions
Do I have to tell the agent to use HMACSigningSkill?
No. The tool's name and description are in the model's context once the server is connected, so it selects the tool when the question calls for it. Naming it explicitly works too and is useful when you want to force the call.
Does connecting the server expose every tool at once?
Yes — one connection lists the whole VerveKit catalog. Clients with a tool budget can usually filter the list; the credit cost is per call, so an unused tool costs nothing.
What does a call cost?
1 credit each time the tool actually runs. A model that reasons about the tool without calling it costs nothing.
Is there a REST version of this?
Yes — the same source is available as a plain HTTPS endpoint on APIVerve, linked above. Same data, same credits, same account.