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

Annotations cover the safety profile (readOnlyHint, openWorldHint), and the description meaningfully adds the return payload (hierarchy, heading, text capped at 50,000 chars, last-amended date, official URL), the data coverage, and the x402 payment model where failed calls are not charged. The payment/charging behavior is important context an agent cannot get from annotations.

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?

Four sentences, front-loaded with the core purpose, and each sentence carries information (modes, return fields, coverage, pricing). No filler, though the coverage sentence is marginally expendable relative to the rest.

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 an output schema present and safety annotations supplied, the description need not explain return values, yet it still summarizes them. It covers the payment/auth requirement, data coverage, and both call modes; only edge cases like conflicting/partial parameter sets are unaddressed.

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 description coverage is 100%, so the baseline is 3, but the description adds real value by grouping the parameters into two invocation modes (q for search vs. title/part/section for section lookup), a pairing the schema does not express. It also notes the 50,000-character text cap, which is a response-side constraint tied to usage.

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 specific verbs (searches, retrieves) and a precise resource (US eCFR via the official API), and clearly separates two operating modes: keyword search vs. single-section lookup. It does not name or differentiate from the adjacent sibling law_federal_register, which covers a different legal corpus, so it falls short of a 5.

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 implies how to select a mode (use q for keyword search; title/part/section for section retrieval) but never states when to prefer this tool over siblings or when not to use it. Usage is inferable from the mode framing rather than explicitly guided.

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