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SmartTools

by io.github.9thShini
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JWT decoder

jwt_decoder

Decode a JSON Web Token's header and payload (base64url). Does NOT verify the signature — that needs the secret/key. Runs on smart-tools.xyz.

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_decoder"
  }
}

Input Schema

NameRequiredDescriptionDefault
tokenYesThe JWT (header.payload.signature)
localeNoLanguage for the source_url link (default en)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.2/5.0
Behavior4/5

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

With no annotations, the description carries the full burden of behavioral disclosure. It reveals a critical limitation (no signature verification) and the decoding mechanism (base64url). It doesn't detail return format or edge cases, but for a simple decoder this is sufficient.

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 two sentences, front-loaded with the purpose, and includes a key caveat. Every word earns its place; 'Runs on smart-tools.xyz' is a minor but acceptable addition.

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 tool with only 2 parameters and no output schema, the description covers the main behavior and the most important limitation. It's complete enough for an agent to select and invoke it correctly, though it could hint at the output structure.

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?

Schema description coverage is 100%, so the schema already documents both parameters well. The description adds no parameter-specific details beyond the schema, earning the baseline score of 3.

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 the tool's function with a specific verb ('Decode') and resource ('a JSON Web Token's header and payload'). It also explicitly notes what it does NOT do (verify signature), distinguishing it from any potential JWT verification tools among siblings.

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 provides clear context (decode JWT header/payload) and an exclusion ('Does NOT verify the signature'), indicating when not to use it. However, it does not explicitly name alternative tools, which would make it a 5.

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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