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

With no annotations, the description carries real weight and delivers: it discloses paid access ($0.001 via x402) and that no network call occurs, which are non-obvious operational facts. It stops short of describing the response shape or error behavior for invalid/odd-length hex, so it isn't fully complete.

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?

Two short, dense sentences with the core capability front-loaded and no padding. The phrase '4-byte selector note' is slightly awkward and the price clause reads as an afterthought, but overall it is efficiently structured.

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 3-parameter tool with no output schema, the description never says what the return looks like, whether multiple 'as' targets produce a combined result, or how failures are signaled. The payment and locality details help, but an agent still has gaps before calling.

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 67%, so the schema documents hex constraints and the request_id idempotency key on its own. The description echoes four of the six 'as' enum values but omits uint256 and bytes, and says nothing about request_id, so it adds only marginal 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?

States a specific verb (decode) and resource (hex) plus the concrete output targets (utf-8, bytes32, address, selector). It doesn't explicitly differentiate itself from siblings like base64 or sha256, but the local-conversion framing is clear enough for selection.

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?

'Local-only' and 'No network fetch (no 4byte.directory)' implicitly tell the agent this won't resolve arbitrary selectors externally, suggesting use when offline/local semantics matter. However there is no explicit 'use this when' guidance or named alternative tool, so usage remains inferred.

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