jwt-validate
Verify and validate JSON Web Tokens (JWTs) by checking signatures, expiration, claims, and structure. Use when the user wants to verify, validate, or check a JWT — e.g. "verify this token", "is this JWT valid", "check the signature", "validate this token against my JWKS", "is this token expired". Supports HMAC, RSA, and ECDSA with secrets, PEM keys, or JWKS endpoints.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/jsonwebtoken/jwt-skills --skill jwt-validate- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads jwt-validate automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
JWT Validate
Verify a JWT's signature and validate its claims. Confirms the token is authentic, unexpired, and structurally sound.
Validation Order
Check in this order. Stop and report at the first failure.
1. Structure
- Exactly 3 dot-separated parts, each valid base64url
- Header and payload parse as valid JSON
- Header contains
alg;algis notnone(unless explicitly expected)
2. Claims
expmust be in the future (report time until expiry or how long ago it expired)nbfmust be in the past or presentiatmust be in the past; flag if > 30 days oldiss,aud,sub— if user provides expected values, they must match- Allow 60 seconds clock skew tolerance on all time checks
3. Signature
Requires the user to provide a secret, PEM public key, or JWKS URI. Always pass secrets and tokens via inline env vars to avoid shell history exposure.
Node.js (preferred):
First, ensure jose is available — install it globally if missing:
node --input-type=module -e "await import('jose')" 2>/dev/null || npm install -g jose
Then verify the token:
JWT_TOKEN='the.jwt.here' JWT_SECRET='user-provided-secret' node --input-type=module -e "import {jwtVerify} from 'jose'; try { const {payload}=await jwtVerify(process.env.JWT_TOKEN, new TextEncoder().encode(process.env.JWT_SECRET), {algorithms:['HS256'],clockTolerance:60}); console.log('VALID'); console.log(JSON.stringify(payload,null,2)); } catch(e) { console.log('INVALID:',e.message); }"
Python:
JWT_TOKEN='the.jwt.here' JWT_SECRET='user-provided-secret' python3 -c "
import jwt,json,os
try:
d=jwt.decode(os.environ['JWT_TOKEN'],os.environ['JWT_SECRET'],algorithms=['HS256'],leeway=60)
print('VALID'); print(json.dumps(d,indent=2))
except Exception as e: print(f'INVALID: {e}')
"
JWKS verification (Node.js):
JWT_TOKEN='the.jwt.here' JWKS_URI='https://example.auth0.com/.well-known/jwks.json' node --input-type=module -e "import {jwtVerify,createRemoteJWKSet} from 'jose'; try { const {payload}=await jwtVerify(process.env.JWT_TOKEN, createRemoteJWKSet(new URL(process.env.JWKS_URI)), {algorithms:['RS256']}); console.log('VALID'); console.log(JSON.stringify(payload,null,2)); } catch(e) { console.log('INVALID:',e.message); }"
If no secret/key is provided, perform structure + claims validation only, and clearly state the signature was NOT verified.
Output Format
## JWT Validation Report
Structure: PASS
Claims: PASS — exp 2025-06-15T12:00:00Z (expires in 2h)
Signature: PASS — RS256, key kid "abc123"
Result: VALID
On failure:
## JWT Validation Report
Structure: PASS
Claims: FAIL — exp 2024-01-15T12:00:00Z (expired 6 months ago)
Signature: SKIPPED
Result: INVALID — token expired
Security Rules
- Never trust the token's
algheader for verification. Always use the algorithm the user expects or that matches the provided key type. Trusting the header enables algorithm confusion attacks where an attacker switches RS256 to HS256 and signs with the public key as an HMAC secret. - Always specify
algorithmsas an explicit allowlist in verification calls. Never passalgorithms: [decoded.header.alg]. - Never pass secrets/tokens as literal command-line arguments. Use environment variables. Args are visible in shell history and
psoutput. alg: none— Flag as a critical security issue. The token is unsigned and cannot be trusted.- If no key is provided, validate structure and claims only. Clearly state: "Signature was NOT verified — token authenticity is unknown."
FAQ
What does the jwt-validate skill do?
Verify and validate JSON Web Tokens (JWTs) by checking signatures, expiration, claims, and structure. Use when the user wants to verify, validate, or check a JWT — e.g. "verify this token", "is this JWT valid", "check the signature", "validate this token against my JWKS", "is this token expired". Supports HMAC, RSA, and ECDSA with secrets, PEM keys, or JWKS endpoints.
How do I install jwt-validate?
Run npx skills add https://github.com/jsonwebtoken/jwt-skills --skill jwt-validate in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/jwt-validate/ (personal) or .claude/skills/jwt-validate/ (project).
Which AI agents can use jwt-validate?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is jwt-validate safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains jwt-validate?
It is published by jsonwebtoken in jsonwebtoken/jwt-skills. It has 628 recorded installs.
More from jsonwebtoken/jwt-skills
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