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

Beyond annotations, the description discloses the paid nature of the call ($0.005 per call in USDC on Solana via x402) and the exact MCP payment flow, including the PaymentRequired challenge and retry mechanism. It also documents the HTTP equivalent endpoint. These are important behavioral traits not captured by 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?

The description is front-loaded with the core operation and then provides payment details. The payment mechanism is necessarily detailed for a paid tool, and the HTTP equivalent is extra but useful. It is appropriately sized overall.

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 one simple parameter and no output schema, the description covers the essential operation, its exclusion of signature verification, and the payment flow. It could briefly describe the decoded return shape, but the missing detail is minor for such a low-complexity tool.

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?

The input schema has 100% description coverage, but the parameter description is only the tautological string 'string'. The tool description implies that the 'token' parameter is a JWT, but it does not add syntax, format, or validation details beyond that implication.

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 states a specific verb and resource: 'Decode a JWT header+payload'. It also scopes the operation by clarifying '(no signature verification)', so an agent can immediately tell this apart from tools that might validate or verify JWTs.

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 description gives clear usage context by stating that it decodes only and explicitly excludes signature verification. It does not name an alternative verification tool, but the scope limitation is enough to know when this tool is not appropriate.

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