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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description goes further and discloses non-obvious traits: Markdown fidelity, the 20 KB body cap with a `truncated = true` flag, and error behavior on unknown slugs. These are exactly the runtime behaviors an agent cannot infer from the annotations or schema.

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 dense sentences with zero filler: output shape first, then routing guidance, then edge-case behavior. Every sentence carries distinct information and the most decision-relevant content (what you get, when to call it) is front-loaded.

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?

Output schema exists, so return-value documentation is not required, yet the description still characterizes the response adequately. For a single-required-param read tool with full schema coverage and rich annotations, nothing an agent needs to call it correctly 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% and the slug description already covers provenance (search_news items[].slug, last segment of a /news/<slug> url), which sets the baseline at 3. The description adds that the input may be given as the slug 'or the /news/ url' (full URL rather than just the trailing segment), which is a mild but real clarification beyond the schema's wording.

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 ('Get one CarRentalList news article') and enumerates the return payload (Markdown with headings/lists/links, date, related makes, source URL). It also implicitly separates itself from search_news by framing this as the detail-fetch step. An agent can distinguish it from the other siblings without opening a 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?

Gives an explicit when-to-use condition ('details of a story found with search_news, or names an article from carrentallist.com/news') and an explicit recovery path ('An unknown slug returns an error; call search_news'). Both the trigger and the fallback alternative are named, leaving nothing to inference.

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