agent-utils-mcp

tool_jwt_decode

Decode a JWT payload to inspect its contents without verifying the signature.

Instructions

Decode a JWT payload without verification (inspection only).

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": "tool_jwt_decode"
  }
}

Input Schema

Name	Required	Description	Default
`token`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 7, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations provided, the description carries the behavioral disclosure burden. It transparently states that verification is not performed, which is the most important behavioral limitation. It does not describe failure modes for malformed tokens, but the output schema may cover edge cases.

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, front-loaded sentence with no filler. Every word adds value: 'Decode', 'JWT payload', 'without verification', and 'inspection only' all convey essential information.

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, single-parameter utility with an output schema present, the description covers the core context: what the tool does and what it does not do. It could add explicit cancellation of verification against a signing key, but the 'without verification' phrase adequately fills that gap.

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 0% description coverage, so the description must compensate. It clarifies that the 'token' parameter is a JWT and that the payload is the decoded result, which gives partial meaning. However, it does not specify whether the full JWT or just the payload part should be passed, leaving some ambiguity.

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 states a specific verb ('Decode'), a specific resource ('JWT payload'), and a critical scope qualifier ('without verification, inspection only'). It clearly distinguishes this from any verification or encoding tool.

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

Usage Guidelines4/5

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

The description implicitly tells the agent when to use this tool: when JWT inspection is needed without signature verification. It does not explicitly mention alternatives or exclusions, but the 'inspection only' phrase provides enough context for a simple utility.

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

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