# JWT Decoder & Verifier MCP for AI Agents AI Agent Connect

> JWT Decoder & Verifier lets your AI client handle the hard math of cryptographic signature checks. While an agent can read a token's content, it can't tell if that content was forged or if the signature is actually valid. This Connector bridges that gap, allowing you to verify API keys and session tokens locally and instantly.

## Overview
- **Category:** fort-knox
- **Price:** Free
- **Endpoint:** https://edge.vinkius.com/vk_preview_D5R4DSb6SK0l9HMwb0HCmTETZzhB9BBHQbV1DXPU/ai-agent-connect
- **Tags:** jwt, cryptographic-verification, token-validation, authentication, security, signature-check

## Description

The JWT Decoder & Verifier handles the cryptographic signature checks that AI agents normally can't do. While your agent can easily read the contents of a JSON Web Token, it has no way of knowing if that token was actually signed by your backend or forged by someone else. This Connector handles the math by offloading it to the V8 engine. It allows your agent to cross-reference a token against a secret or public key to confirm it's legitimate. When you're browsing the Vinkius catalog, this is the specific tool you need when you want to move past just reading data and into actual security verification. It handles the signature validation offline, which keeps your keys private and your auth checks accurate. You get a clear answer on whether a token is real, expired, or tampered with without ever sending your keys over the wire. It is about moving from guessing to knowing because the math actually checks out. Instead of copying and pasting tokens into online decoders that might log your data, you can stay entirely within your local environment. Your agent becomes a more capable security partner, able to audit your auth flows and verify third-party webhooks with total confidence.

## Tools

### decode_jwt
Pass a JWT and secret key to verify the signature and extract the payload. This blocks forged tokens.

## Prompt Examples

**Prompt:** 
```
Check if this token is valid with my secret key: [key]
```

**Response:** 
```
### Token Verification

| Property | Status |
| :--- | :--- |
| **Signature** | ✅ Valid |
| **Expiration** | 2026-01-01 |
| **Issuer** | Auth0 |

**Result:** The token is cryptographically authentic and currently active.
```

**Prompt:** 
```
What's inside this token?
```

**Response:** 
```
### Decoded Payload

- **User ID:** 12345
- **Roles:** `admin`, `editor`
- **Scopes:** `read:files`, `write:files`
- **Expires At:** 2025-12-31T23:59:59Z

*Note: Signature has been verified as valid.*
```

**Prompt:** 
```
Why is this token failing?
```

**Response:** 
```
### Verification Error

❌ **Status:** Invalid

**Reason:** `TokenExpiredError`
The token expired on **2024-01-01**. You will need to request a new session token from the identity provider.
```

## Capabilities

### Verify cryptographic signatures
Confirm if a token was signed by your authorized key.

### Extract user roles from tokens
Pull specific permissions and roles directly from the payload.

### Check token expiration dates
Identify exactly when a session or token will expire.

### Decode header information
Read the metadata and algorithm types used in the token.

### Validate secret keys
Cross-reference tokens against your specific public or secret keys.

### Identify payload claims
Get the full list of user IDs and other data inside the token.

## Use Cases

### Debugging a failing login
A developer asks the agent to check why a token is rejected; the tool confirms the signature is invalid.

### Webhook validation
A user wants to ensure a Stripe webhook is real; the agent uses the tool to check the signature against a secret.

### Permission auditing
An admin asks the agent to list roles in a batch of tokens; the tool extracts them from the payload.

### Expiry checks
A developer wants to see how long a specific session lasts; the tool identifies the exact expiration timestamp.

## Benefits

- Stop trusting forged tokens because the decode_jwt tool performs actual math on the signature.
- Keep your secrets local since the verification happens on your machine rather than over a network.
- Get instant feedback on token expiration to catch session bugs before they hit production.
- Simplify your auth debugging by having your agent extract roles and IDs directly from the payload.
- Reduce the risk of security leaks by offloading complex crypto logic from the AI's reasoning loop to a dedicated engine.

## How It Works

The bottom line is you get cryptographically sound token validation without trusting the AI to guess the security.

1. Connect your AI client to the JWT Decoder & Verifier.
2. Provide the JWT string and your secret or public key.
3. Get a confirmation of the signature's validity and the decoded content.

## Frequently Asked Questions

**Can the JWT Decoder & Verifier check if a token is forged?**
Yes, it performs a cryptographic signature check against your secret or public key to ensure the token is authentic.

**Does the JWT Decoder & Verifier work offline?**
Yes, all decoding and verification happen locally on your machine, so your keys never leave your environment.

**Can I use the JWT Decoder & Verifier for my private API keys?**
Yes, you can provide your secret key to the tool to verify the integrity of your private API tokens.

**Is the JWT Decoder & Verifier safe for my secrets?**
Yes, because it processes everything locally. It does not send your keys or tokens to any external service.

**How does the JWT Decoder & Verifier handle expired tokens?**
It automatically checks the expiration claim and will notify you if the token is no longer valid.

**Can the JWT Decoder & Verifier read user roles?**
Yes, it extracts all claims from the payload, including user IDs, roles, and permission scopes.

**Can I decode a token without the secret?**
Yes, if you omit the secret, it will only decode the payload, but it will not verify authenticity.

**Does it check expiration dates?**
Yes, if the secret is provided, it will automatically throw an error if the token is expired.

**What algorithms does it support?**
It supports standard JWT algorithms including HS256, HS384, and HS512.