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

With readOnlyHint=true and openWorldHint=false already declaring the safety profile, the description still adds a substantive behavioral fact not in the annotations: the signature is NOT verified, so results are untrusted. The 'pure computation, free' note adds cost/latency context. Missing only notes on malformed-token behavior.

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?

Three short clauses, front-loaded with the operation and the most important caveat (no signature verification) before the safety warning and cost note. Every sentence earns its 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 one-parameter, no-output-schema tool this covers operation, trust level, and safety. The one gap is return shape — whether the result is a JSON object with separate header/payload fields or raw text — which the absent output schema leaves undocumented.

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 0% for the single 'token' parameter, so the description must carry the semantics. 'Decode a JWT header and payload' implies the input is a JWT string, but it does not state the expected format (compact JWS, three dot-separated segments) or what happens with a non-JWT input.

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 (Decode) and resource (JWT header and payload) and immediately delimits scope with 'WITHOUT verifying its signature'. An agent can tell exactly what operation it is getting, and no sibling among the many conversion/validation tools overlaps with JWT decoding.

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?

'Do not paste live secrets' gives a clear usage constraint, and the absence of any JWT verification tool in the sibling list means there is no alternative to route away from. It stops short of explicitly saying when to reach for this versus, e.g., a JSON formatter on a decoded payload, but the context is clear.

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