Decode a JWT token to display its claims without signature verification.
Decode and display the claims in a JWT token (without signature verification)
| Name | Required | Description | Default |
|---|---|---|---|
| token | Yes | JWT token to decode |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it discloses the most important behavioral trait: this tool does not verify signatures, meaning it will decode tokens regardless of validity. It also implies a read-only, non-mutating operation by saying 'decode and display', which is sufficient for this simple tool.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, front-loaded sentence that conveys the action, the target resource, and the key limitation with zero wasted words.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a single-parameter tool with no options and no output schema, the description adequately covers what the tool does and its key caveat. It could mention what happens with malformed tokens or the exact return shape, but the minimal complexity makes the current description sufficient for correct invocation.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The schema already covers the only parameter with a description ('JWT token to decode'), and the tool description adds no new semantic detail such as expected format, error behavior, or edge cases. With 100% schema coverage, a baseline of 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description uses a specific verb ('Decode and display') with a clear resource ('claims in a JWT token'), and immediately distinguishes itself from signature verification via the parenthetical. This makes the tool's purpose unambiguous even among siblings like verify_token and generate_token.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The phrase 'without signature verification' clearly tells an agent that this tool is for inspection, not validation, which is a useful usage boundary. However, it stops short of explicitly naming verify_token as the alternative or stating when verification should be used instead.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.