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

Goes well beyond the annotations: discloses that the check is offline, that malformed signatures return 400 and are uncharged, that successful calls cost $0.01 via x402 USDC or a card key, that the first 25 are free, and that failed calls are free. Crucially it explains why repeats are not free, which reconciles with idempotentHint=false and adds real decision-relevant context.

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-loaded with the core purpose and scope before pricing and error details; nearly every sentence carries information an agent needs (limits, cost, error handling). It is dense and slightly crammed with payment mechanics, but nothing is truly redundant.

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 still explains what comes back (recovered signer address plus a match verdict when an expected address is supplied), what happens on bad input (400, uncharged), and what class of signatures are unsupported. That is enough for an agent to call it correctly and interpret the result.

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 all four parameters (message, signature, address, raw) are already documented in the schema, including the raw-bytes flag and the 65-byte signature format. The description confirms the meaning of the optional expected address ('say whether it matches') but adds no syntax or edge-case detail beyond the schema, so 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?

States a specific verb and resource ('verify an Ethereum personal_sign (EIP-191) signature: recover the address... say whether it matches'), including the exact output semantics. It also delimits scope by ruling out ERC-1271 smart-contract wallets, so an agent can distinguish this from any other crypto/EVM helper in the catalog.

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 concrete use cases (sign-in-with-wallet, proving wallet ownership, checking a signed order) and an explicit exclusion (contract wallets signing via ERC-1271 are not covered by this offline check). It stops short of naming a sibling tool as the alternative for that excluded case, which keeps it from a 5.

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