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

Annotations already declare readOnly, idempotent, non-destructive, and open-world behavior, but the description adds material context: public openchain database with 4byte.directory fallback, verified-contract signatures returned first, and a $0.005 USDC x402 charge on eip155:8453. This is exactly the kind of behavioral and payment detail an agent needs before invocation.

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?

Three sentences, front-loaded with the action and formats, then source and ordering, then price. Every sentence carries operational value with 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?

For a single-parameter read-only lookup with rich annotations and no output schema, the description is complete: it explains the lookup source, fallback behavior, result ordering, accepted input formats, and x402 payment requirement. Nothing essential for correct invocation 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 coverage is 100%, so the baseline is 3, but the description adds useful format detail beyond the schema: selectors are 0x + 8 hex and event topics are 0x + 64 hex, up to 20 items. The schema already covers array/string and comma separation, so this is a meaningful but not exhaustive enhancement.

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: reverse-look up 4-byte selectors and 32-byte event topics to signatures. The word "reverse" distinguishes it from the forward-signature sibling evm_selector, and the scope is clear 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?

The usage context is implied: use this when you already have selectors or event topics and need candidate signatures. However, it does not explicitly name when-not-to-use cases or the alternative evm_selector for forward lookups, nor does it state prerequisites beyond the x402 price.

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