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

Annotations already establish read-only, non-destructive, closed-world behavior, and the description adds substantial value on top: the exact output shape (ISO times for iat/nbf/exp, expiresIn, issuer/subject/audience) and a concrete enumeration of security findings it surfaces (alg none, HS* with URL-like kid, off-site jku/x5u, oversized payloads, sensitive field names). That is far beyond annotation coverage.

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?

Purpose is front-loaded and every clause carries information — the difference is that the return/findings enumeration is packed into one long run-on sentence rather than being broken out, which slightly hurts scanability but wastes no words.

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 must describe returns, and it does so in detail, including the findings taxonomy. For a single-parameter, read-only tool this leaves nothing an agent needs 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?

One parameter at 100% schema description coverage, so the schema already documents the token format and the ignored 'Bearer' prefix. The description adds no parameter-level detail beyond the schema, which is the expected baseline here.

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) plus the critical scope limit that the signature is not verified. No sibling does anything similar, and the tool's boundary is unambiguous.

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 parenthetical 'it never takes a secret' and 'without verifying the signature' effectively tell the agent when NOT to reach for this tool (any real trust/verification decision). It stops short of naming an alternative verification path, but no sibling offers one, so context is adequate.

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