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

With readOnlyHint already covering the safety profile, the description adds substantial context: alg none/HS/jku/x5u flagging behavior, the no-verification limitation, and a full pricing/charging model (failed calls not charged). This is rich disclosure beyond the annotations.

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?

Front-loaded with the core action and output, followed by limitations and pricing. Dense but every clause carries meaning; the pricing sentence is long yet relevant to invocation decisions.

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 an output schema present, return values needn't be explained, and the description fully covers behavior, limitations, security flags, and cost. Nothing an agent needs to call it correctly 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 coverage is 100% with a single fully documented token parameter, so the schema does the heavy lifting. The description adds the base64url JSON / compact header.payload.signature framing, but no format details beyond the schema, so baseline 3 is appropriate.

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 (a JWT you supply), then enumerates exactly what it reports: algorithm, key id, claims, and time checks. This is unambiguous and clearly distinguishable from the network/DNS/blacklist siblings.

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?

It gives explicit scope boundaries — it does not verify the signature (no key given) and does not fetch the key URL — which tells the agent what this tool will not do. There's no direct sibling alternative to route to, but the exclusions provide clear usage context.

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