# JWT Payload Extractor MCP for AI Agents MCP

> JWT Payload Extractor lets you peek inside JSON Web Tokens without needing the secret key. It decodes payloads and checks expiration dates instantly through your AI client.

## Overview
- **Category:** developer-tools
- **Price:** Free
- **Endpoint:** https://edge.vinkius.com/vk_preview_ZDWvfAAQYs5wuqUcHTycNIaN4acsQhRWK43rr8eY/mcp
- **Tags:** jwt, auth, decoding, payload, token

## Description

You're debugging an auth flow and see a massive, encoded string in your network logs. Instead of hunting for a web-based decoder or manually pasting strings into a browser console, you just hand the token to your agent. This MCP handles the heavy lifting by splitting the segments, normalizing the Base64URL encoding, and turning that unreadable mess into clear JSON. You can grab specific user IDs, check when a session is set to expire, or verify claims like roles and permissions. It's part of the Vinkius catalog, so you get instant access alongside thousands of other specialized tools. No more manual decoding or guessing if a token is still valid; just get the data you need directly in your workflow.

## Tools

### extract_token_identity
Pulls a single, specific claim like a user ID or role from a token. It saves you from reading through the whole payload.

### check_token_expiry
Checks if a specific JWT has passed its expiration timestamp. It's great for quickly seeing if a session is still valid.

### decode_jwt_payload
Decodes the entire payload segment of a JWT string into readable JSON. Use this to see all claims at once.

## Prompt Examples

**Prompt:** 
```
Can you tell me what's inside this token? eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT3fwpMeJf36POk6yJV_adQssw5c
```

**Response:** 
```
The payload contains the following information:

* **Subject (sub):** 1234567890
* **Name:** John Doe
* **Issued At (iat):** 1516239022
```

**Prompt:** 
```
Is this token still valid? eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE1MTYyMzkwMjJ9.signature
```

**Response:** 
```
**Status:** Expired

The expiration timestamp is 1516239022, which has already passed.
```

**Prompt:** 
```
What is the user role in this JWT? eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX3JvbGUiOiJhZG1pbiJ9.signature
```

**Response:** 
```
The `user_role` claim is set to **admin**.
```

## Capabilities

### Read encoded payloads
Turns unreadable JWT strings into readable JSON objects.

### Verify session lifespan
Checks the expiration timestamp against the current time to see if a token is still active.

### Isolate user identities
Pulls specific claims like subject or custom IDs from the token data.

## Use Cases

### Debugging expired sessions
A developer sees a 401 error and asks their agent if the token is still valid using check_token_expiry.

### Verifying user permissions
An engineer needs to confirm a 'role' claim is present in a new auth flow by using decode_jwt_payload.

### Automating identity checks
A tester uses extract_token_identity to ensure the correct subject ID is being passed in a test suite.

## Benefits

- Stop manual decoding: Use decode_jwt_payload to see claims without using external websites.
- Instant expiration checks: Quickly run check_token_expiry to debug session timeout issues.
- Targeted data retrieval: Pull exactly what you need with extract_token_identity instead of parsing JSON manually.
- No secret keys required: Inspect the payload structure even when you don't have access to the signing key.
- Cleaner debugging: Keep your sensitive token data within your local AI client environment.

## How It Works

The bottom line is you get instant visibility into token contents without needing cryptographic keys.

1. Paste your encoded JWT string into your AI client.
2. The MCP splits the token and normalizes the Base64URL encoding.
3. You receive the decoded payload or specific claim values in plain text.

## Frequently Asked Questions

**How can I use JWT Payload Extractor to see my user data?**
You simply provide the encoded token to your AI client, and it will decode the payload so you can read all the claims like user IDs or roles.

**Does JWT Payload Extractor verify if a token is authentic?**
No, this MCP only decodes the content. It does not perform cryptographic signature verification to check if the token was tampered with.

**Can I use JWT Payload Extractor to find out when a session ends?**
Yes, you can use it to inspect the expiration claim and see exactly when the token is set to expire.

**Is JWT Payload Extractor useful for checking permissions?**
Absolutely. You can use it to quickly pull specific permission or role claims from a token to verify your auth logic.

**Do I need to provide my private keys to JWT Payload Extractor?**
No, you only need the encoded JWT string itself. The tool decodes the payload without needing any secret keys.

**Does this tool verify the JWT signature?**
No, the server focuses exclusively on the deterministic parsing of the payload segment. It does not utilize any cryptographic primitives or secret keys to validate the integrity of the signature segment. Tools available: `decode_jwt_payload`, `check_token_expiry`, `extract_token_identity`.

**How can I see the expiration date of a token?**
The server extracts the 'exp' claim from the decoded JSON object and compares its Unix timestamp against the current system time to identify if the token's operational window has expired.

**Can I extract specific user IDs from the token?**
Yes. After parsing the payload segment into a JSON structure, the server traverses the object hierarchy to retrieve the value associated with any specified key, such as 'sub' or custom user identifiers.