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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the description correctly focuses elsewhere and adds real value: the external data source (4byte.directory), the per-call price, the x-credit-token prepaid path, and the 1 free call/day tier. The word 'candidate' usefully signals that multiple signatures may be returned.

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 example, then details. The pricing sentence is long but every clause (price, prepaid header, free tier, no API key) is decision-relevant for an agent that has to pay per call. Minor density but no filler.

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?

An output schema exists, so return-value explanation is rightly omitted. Combined with annotations for safety and the description's coverage of cost, auth, and data source, an agent has what it needs. Slightly short on ambiguity handling (multiple candidates, collision cases) but otherwise complete.

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 a 3 is the baseline, but the description goes slightly beyond the schema's terse 'Function selector' by stating the parameter is required and that it accepts either a bare 4-byte selector or full calldata, which is meaning the schema alone does not convey.

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/resolve) and resource (4-byte function selector) and illustrates it with a concrete example '0x70a08231'. The direction of conversion is unambiguous, making it trivially distinguishable from the reverse-direction sibling encode_selector.

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 clarifies the accepted input shapes ('bare selector or full calldata'), which implies usage, and gives pricing/free-tier context. However it never states when to reach for this versus alternatives such as encode_selector or tx_decode, and gives no exclusions.

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