JWT Decoder Skill

Overview

On paid plans, pass a PEM public key, certificate or JWK as publicKey to verify RS, PS, ES and EdDSA signatures and check exp and nbf. HMAC (HS*) secrets and alg none are always refused, and keys are never fetched from URLs.

Live Test JWT Decoder Skill Skill →

The tool

Once your client is connected to the VerveKit server, this appears in its tool list as JWTDecoderSkill. It is read-only and open-world — it fetches and never mutates anything on your side — so most clients call it without asking you to confirm.

{
  "name": "JWTDecoderSkill",
  "arguments": {
    "token": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6InNhbXBsZS1rZXktMSJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaXNzIjoiaHR0cHM6Ly9hdXRoLmV4YW1wbGUuY29tIiwiYXVkIjoiYXBpLmV4YW1wbGUuY29tIiwiaWF0IjoxNzY3MjI1NjAwLCJleHAiOjIwODI3NTg0MDB9.hP0O9ELZGk-KN3upyYqdOnPY2Ig7FAzfUY_xytzOCBIhn0_TWdzl2dbLPlj0rkCDsRIQX0I5t9Xv551VI1W9dmvRGtVztyeD3IKHnIn24baOUtjU7Eb6FHL_iWMu5PqMeQJPFytuYbYhzjjCNfFPgAciGgn1Celr8H7_q51x5naMb-nbTvBc5SIX9MBnegGzabExBYQ-OsdKOoYmK0uymNIgC3834jlPuhuJHkPsxX7ncKoSQ4wheiLaZDwFANlT1NrD2XgKyyh-LIIg9CRwqB_WDktZ_R6UusNkLRhKJ20ff29ttkyRhJZzEqRRK60xYn7iPyg4YQni1J_w-oAa_w"
  }
}

You do not name the tool yourself; the model picks it. Asking about eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6InNhbXBsZS1rZXktMSJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaXNzIjoiaHR0cHM6Ly9hdXRoLmV4YW1wbGUuY29tIiwiYXVkIjoiYXBpLmV4YW1wbGUuY29tIiwiaWF0IjoxNzY3MjI1NjAwLCJleHAiOjIwODI3NTg0MDB9.hP0O9ELZGk-KN3upyYqdOnPY2Ig7FAzfUY_xytzOCBIhn0_TWdzl2dbLPlj0rkCDsRIQX0I5t9Xv551VI1W9dmvRGtVztyeD3IKHnIn24baOUtjU7Eb6FHL_iWMu5PqMeQJPFytuYbYhzjjCNfFPgAciGgn1Celr8H7_q51x5naMb-nbTvBc5SIX9MBnegGzabExBYQ-OsdKOoYmK0uymNIgC3834jlPuhuJHkPsxX7ncKoSQ4wheiLaZDwFANlT1NrD2XgKyyh-LIIg9CRwqB_WDktZ_R6UusNkLRhKJ20ff29ttkyRhJZzEqRRK60xYn7iPyg4YQni1J_w-oAa_w in the terms this skill covers is enough for it to reach for JWTDecoderSkill on its own — naming it explicitly also works, and is the way to force the call.

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/mcp

Per-client setup — Claude, 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. Premium arguments are accepted on every plan but only take effect on plans that include them.

What the model gets back

The result carries a structuredContent object matching the tool's declared outputSchema, so a client reads fields without parsing prose. status is "ok" and error is null on success; a null field means the value was not available for that input, not that the call failed.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44

{
  "status": "ok",
  "error": null,
  "data": {
    "header": {
      "alg": "RS256",
      "typ": "JWT",
      "kid": "sample-key-1"
    },
    "payload": {
      "sub": "1234567890",
      "name": "John Doe",
      "iss": "https://auth.example.com",
      "aud": "api.example.com",
      "iat": 1767225600,
      "exp": 2082758400
    },
    "signature": "hP0O9ELZGk-KN3upyYqdOnPY2Ig7FAzfUY_xytzOCBIhn0_TWdzl2dbLPlj0rkCDsRIQX0I5t9Xv551VI1W9dmvRGtVztyeD3IKHnIn24baOUtjU7Eb6FHL_iWMu5PqMeQJPFytuYbYhzjjCNfFPgAciGgn1Celr8H7_q51x5naMb-nbTvBc5SIX9MBnegGzabExBYQ-OsdKOoYmK0uymNIgC3834jlPuhuJHkPsxX7ncKoSQ4wheiLaZDwFANlT1NrD2XgKyyh-LIIg9CRwqB_WDktZ_R6UusNkLRhKJ20ff29ttkyRhJZzEqRRK60xYn7iPyg4YQni1J_w-oAa_w",
    "isExpired": false,
    "expiresAt": "2036-01-01T00:00:00.000Z",
    "issuedAt": "2026-01-01T00:00:00.000Z",
    "tokenAge": "309 days",
    "algorithm": "RS256",
    "expiresIn": 288757380,
    "notYetValid": false,
    "securityAnalysis": {
      "isUnsecured": false,
      "hasExpiration": true,
      "isLongLived": true,
      "issues": [
        "Token lifetime exceeds 24 hours"
      ]
    },
    "warning": "Signature verified with the supplied public key.",
    "signatureVerification": {
      "verified": true,
      "algorithm": "RS256",
      "keyType": "RSA",
      "reason": null,
      "claimsValid": true,
      "claimsReason": null
    }
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Failure modes

Errors come back as tool errors carrying a sentence the model can act on, not a bare status code. Error handling covers the full list.

A call costs 1 credit each time the tool actually runs; a model that reasons about the tool without calling it costs nothing.

Use cases

Token Debugging

Debug and inspect JWT tokens during development to view header and payload contents

Token Analysis

Analyze token structure and claims for free, and verify the signature against a public key on paid plans

Expiration Check

Check token expiration status and view expiration timestamps

Token Inspection

Inspect token contents for troubleshooting authentication issues

Other ways to use JWT Decoder Skill

Set up JWT Decoder 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.

Related

More in Data Conversion: