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

With no annotations provided, the description carries the full burden and does disclose the critical traits: no key required, no signature verification, deterministic, and free/no payment. It does not cover malformed-token error behavior or whether decoding is strict about base64url padding, so it is strong but not complete.

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?

One compact sentence plus a short routing clause; the free/no-payment qualifier and the no-signature caveat are front-loaded where the agent will see them first. Nothing is wasted.

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 deterministic utility with no output schema, the description supplies the key limitation (no signature verification) and the return intent (header and payload claims). Minor gaps remain: it does not state the output shape explicitly or what happens on an invalid token, but nothing critical to correct invocation is missing.

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 schema already includes an example token value, so the single parameter is fully documented structurally. The description adds no syntax, format, or validation detail about the token beyond what the schema provides, so the 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 and resource ('Decode a JWT') plus the exact scope ('parse header and payload claims without a key'). This clearly separates it from adjacent siblings like u_base64 or u_json, which an agent could otherwise confuse for JWT work.

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 description bounds usage by stating 'no signature verification', which tells the agent not to rely on this for trust decisions, and it names the transport options (MCP or POST /u/jwt). However, it never says when to prefer this over sibling utilities such as u_base64 when a user just wants to peek at a token, so usage is implied rather than explicit.

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