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

Goes well beyond the annotations by disclosing the one-hour lifetime, the one-per-wallet limit, no-account signature ownership, and the exact recovery flow for the auth message (send a placeholder signature and read details.expected). It even specifies both signature encodings (EIP-191 and solana:<pubkey>:<sig>), which is exactly the behavioral detail an agent needs.

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 'FREE' scope well and keeps the core mechanics tight, but the closing paragraph about POST /feedback is off-topic for this tool and inflates the description without helping an agent call free_inbox correctly.

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 carries the return burden and does explain the expected refusal payload (details.expected), but it does not describe what a successful call returns (e.g., the inbox address/identifier or expiry representation). Otherwise complete for a 3-required-param signed request.

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%, so the baseline is 3, but the description adds meaning beyond the schema: it explains that the signature is proof over the server-named message and how to obtain that message, plus the two accepted signature forms. This is real added value over the generic schema descriptions.

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 action and resource: claim one free live inbox per wallet for one hour. It explicitly differentiates from its close sibling create_inbox ('A sibling of create_inbox, not a discount on it'), so an agent can disambiguate without opening either 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?

Gives clear context: use this to receive one code before paying for the 24 h tier, and states the quota constraint (one address, one hour, next one must be bought). It does not spell out the explicit fallback condition for choosing create_inbox instead, but the routing intent is unambiguous.

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