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

Annotations already declare the safe-read profile (readOnly, idempotent, non-destructive, open world), so the bar is low, yet the description still adds real behavior: the exact field set returned for a number (title, status, date, authors, abstract, plus obsoletes/is-obsoleted-by/updates/is-updated-by), and the capped result count ('up to five') for title searches. That limit and the two-mode return shape are not derivable 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?

Front-loaded with the trigger condition, followed by parameter rules and then return-shape behavior. Every sentence carries distinct information, and the two-mode contrast is expressed economically.

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?

Despite an output schema existing, the description usefully summarizes per-mode results and the follow-up pattern, which is exactly what an agent needs to chain calls. Requirements, exclusions, and both invocation modes are covered with no gaps.

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 earns above baseline by explaining the semantic consequence of each parameter: a number yields full detail metadata, title words yield a short list of up to five numbered matches. The 'not both' constraint is reinforced here as well as in 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 and resource ('look up an RFC') and immediately grounds it with concrete example questions, so an agent knows exactly what class of request this covers. Siblings are unrelated utilities, so no differentiation is needed.

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?

Explicitly frames the trigger ('use this when the user asks about an RFC'), gives two natural-language examples, and states the mutual exclusion rule ('Pass either the RFC number, or words from its title (not both)'). It also routes the follow-up: title matches are a two-step flow where you call again with a number.

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