devutils-mcp-server

jwt_decode

Decode JWT tokens to inspect header and payload for debugging, without signature verification.

Instructions

Decode a JWT (JSON Web Token) and display its header and payload without verifying the signature. Useful for debugging and inspecting tokens.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "token": "<token>"
    },
    "name": "jwt_decode"
  }
}

Input Schema

Name	Required	Description	Default
`token`	Yes	The JWT string to decode

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Mar 24, 2026

TDQS

A3.8/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description must fully disclose behavior. It correctly notes that the signature is not verified, a key trait. However, it does not describe the output format or any other behavioral details beyond the basic decode operation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, well-structured sentence that immediately states the main action and key qualification. It is concise and front-loaded with no wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple decode tool with one parameter and no output schema, the description adequately covers purpose, limitations, and use case. It could mention output format, but given the simplicity, it is fairly complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 100% coverage for its single parameter 'token,' which is already described as 'The JWT string to decode.' The description does not add additional meaning beyond what is in the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states that the tool decodes a JWT and displays its header and payload without verifying the signature, which is a specific verb+resource. It distinguishes itself from the sibling tool jwt_validate by noting the lack of signature verification.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description mentions it is 'useful for debugging and inspecting tokens,' which implies usage context but does not explicitly state when not to use it or compare with alternatives like jwt_validate. The guidance is implied rather than explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.