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

The description discloses the exact cost ($0.01 USDC on Base), the payTo address, the fallback service, and the behavior for unknown selectors (paid 200 with found:false). These details go far beyond what annotations (readOnlyHint, openWorldHint) convey and are critical for a paid lookup tool. No contradictions.

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?

The description packs payment, purpose, syntax, edge case, sibling relationship, and limitation into one dense but non-redundant run-on. Everything present is useful, though structure could be improved for readability. Appropriate size for a simple tool.

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?

The tool has one parameter and no output schema, so the description carries the burden of explaining behavior. It covers cost, failure semantics, and limitations, but does not state what a successful result looks like for a known selector. Good but not fully complete regarding return payload.

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 already covers hex with first-4-bytes semantics, so baseline is 3. The description adds that hex= / selector= / data= are accepted key variants, which supplements the schema's single name. This is useful but slightly ambiguous; still, it adds meaning beyond the schema.

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?

Description explicitly states '4-byte function selector lookup via public openchain.xyz (4byte.directory fallback)' – a specific verb and resource pair. It also distinguishes itself from a full ABI decoder and positions itself relative to /tx, making it easy to tell apart from siblings.

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 contrasts with /tx by noting it 'Complements /tx (inputLen only)' and explicitly says 'Not a full ABI decoder', which tells an agent when not to use it. However, it does not enumerate specific use cases or alternative sibling tools beyond these two mentions. Clear enough but slightly implicit.

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