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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), but the description adds genuinely new behavioral context: the per-call price ($0.001), that bad input is refused before any charge, and that the tool yields a request descriptor to be invoked separately via an x402/MPP client. This pricing and error-before-charge disclosure is exactly the kind of extra context annotations cannot express.

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 purpose is front-loaded in the first clause, and the sentences each carry distinct information (capability, invocation model, error behavior). The middle sentence is somewhat overloaded with URL, price, schema, example, and client details, but 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?

With no output schema, the description carries the return-value burden and does so: it lists the decoded fields and expiry status. It also explains the invocation model, cost, and refusal behavior, so an agent has everything needed to call 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?

There is a single parameter with 100% schema description coverage ('JWT header.payload.signature'), so the schema already documents the input format. The description adds no additional syntax or format guidance for the token parameter, which matches the baseline 3 for high-coverage schemas.

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 names a specific verb and resource (decode/inspect a JWT) and enumerates exactly what is produced: header, payload, alg, kid, and iat/nbf/exp as ISO times plus expiry status. It is clearly distinguishable from the sibling utilities (util_base64, util_hash, util_json_validate) and even discloses that the tool returns a paid x402 request descriptor rather than the raw decode.

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?

'Use when you need to inspect a JWT without a key' gives a clear trigger condition, and the description explains the paid two-step flow (call the returned URL with an x402 or MPP client). It does not name an alternative sibling or state when NOT to use it, so it falls short of full when/when-not guidance.

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