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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds material context beyond that: no secrets are needed or stored, a free tier of 10 calls/day, and the paid path via x402 or X-API-Key credits — cost and rate-limit facts an agent needs before calling.

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?

Capability is front-loaded in the first sentence and the security and pricing notes follow in order. The payment boilerplate is somewhat dense but short, and every clause carries a distinct fact.

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?

An output schema exists, so return values need no explanation, and the description covers key sources, algorithms and cost model. The minor gap is that the example token is an HS256 token while only asymmetric algorithms are listed as verifiable, which could confuse an agent about whether HMAC-signed tokens are verifiable.

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%, so all three parameters are already documented, including discover = use iss OIDC discovery. The description confirms the JWKS URL / OIDC discovery duality and adds the supported signature algorithm families, but adds little meaning the schema does not already carry — 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?

The description uses specific verbs (decode, explain claims, verify) against a specific resource (JWT) and names the supported algorithm families RS/PS/ES/EdDSA plus both key sources. It is clearly JWT-specific, though it does not explicitly contrast itself with sibling verifiers such as signature_verify or hmac_verify.

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?

There is no explicit when-to-use or when-not-to-use guidance and no named alternative. The only routing signal is the mention of two key-resolution modes (JWKS URL vs issuer OIDC discovery), which is parameter guidance rather than tool-selection guidance.

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