jwt_decodeDecodes a JWT's header and payload WITHOUT verifying its signature, so its claims must not be trusted on this basis alone. To check authenticity, use jwt_verify.
| Name | Required | Description | Default |
|---|---|---|---|
| token | Yes | The JWT to decode. Decodes header and payload only -- does not verify the signature (use /jwt-verify for that). |
Changes observed during successful MCP inspections.
Input schema / properties / token / descriptionPrevious value: -""New value: +"The JWT to decode. Decodes header and payload only -- does not verify the signature (use /jwt-verify for that)."Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, and non-destructive, so the description is right not to repeat safety metadata. It adds genuinely valuable context beyond annotations: that the signature is unverified and claims must not be trusted on this basis, which is the key behavioral caveat for a security-adjacent 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?
Two front-loaded sentences with zero filler; the security caveat and the routing alternative each earn their place.
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-input decoding tool with no output schema and annotations covering the safety profile, the description supplies the essential caveat and the redirect to jwt_verify. It could say a touch more about the decoded shape (header/payload only), though it already implies this.
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 coverage is 100% and the single 'token' parameter is fully documented in the schema, which even repeats the no-verification caveat. The description adds no format or syntax detail beyond what the schema already provides, so baseline 3 applies.
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?
States a specific verb (decodes) and resource (JWT's header and payload) and immediately distinguishes itself from jwt_verify by scoping what it does NOT do. An agent can pick it apart from jwt_verify without inspecting schemas.
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?
Explicitly names the alternative (jwt_verify) and the condition selecting it ('to check authenticity'). The when-to-use/when-not-to-use split is fully enumerated in two sentences.
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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