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

Goes well beyond annotations by disclosing the charging model: $0.01/call via x402 USDC or card key, first 25 free, failed calls free, and that repeats are not free. This cost and idempotency consequence (paired with idempotentHint=false) is exactly the operational context 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?

Front-loads the return value, then usage, then pricing. Four dense sentences with little waste, though the payment sentence packs several clauses that could be trimmed slightly.

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?

No output schema exists, so the description carries the return contract and does so fully (message, length, server time), while also covering cost and safety. 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 description coverage is 100% and documents the single message parameter with a 2,000-character limit, so the schema does the work. The description only adds a trivial 'Example: message=hello' and no format or constraint detail beyond the schema, so 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?

States a specific verb and resource (returns the message you send) plus the exact payload (length and server time), which no sibling tool does. An agent can distinguish this from text_stats or ping without opening the schema.

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?

Explicitly says to use it for testing an x402 client, payment flow, or agent tool wiring end to end, which is a clear context. It does not name an alternative or exclusion, but for a self-evidently unique echo tool none is needed.

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