Decode a JWT token to inspect its header, payload, claims, signature, and expiry information without performing signature verification.
Decode a JWT token without verification. Returns the header, payload with all claims, signature, and expiry information.
| Name | Required | Description | Default |
|---|---|---|---|
| token | Yes | JWT token string (e.g., "eyJhbGciOiJIUzI1NiIs...") |
Changes observed during successful MCP inspections.
v1.4.2Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark this as read-only, and the description adds a key behavioral caveat: it decodes without verification, which is significant for security-sensitive decisions. It also discloses what information is returned, extending beyond the annotation's simple read-only hint.
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 opens with the core action and scope, then lists the returned components. Every part adds value with no repetition or filler.
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 tool with one parameter and no output schema, the description adequately covers the essential behavior and return values. It could briefly note behavior on malformed tokens, but the current wording is sufficient for an agent to select and invoke it correctly.
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?
Schema description coverage is 100% and the only parameter, token, is already described as a JWT token string with an example. The description reinforces that the input is a JWT and explains the output, but it does not add new meaning to the token parameter itself.
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-resource pair, 'Decode a JWT token', and immediately clarifies the important scope 'without verification'. It also names the decoded components (header, payload, signature, expiry), making the tool's purpose unmistakable even without sibling JWT tools.
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 verification' provides clear contextual guidance: this tool is for decoding only, not for validating tokens. It implies that agents needing signature verification should look elsewhere, though it does not name an alternative tool explicitly.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.