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

Annotations already disclose the safety profile (readOnlyHint=true, destructiveHint=false), so the description is freed to describe output shape: the question, beat-by-beat narration, and per-beat visual types (map, timeline, key figure, bar chart, quote). It also notes the return of a canonical pollar.news URL and the semantics of the 'next' timeline marker. No auth or rate-limit details, but output behavior is well covered.

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 core action and identifier, then enumerates return content efficiently in one long sentence. Slightly dense—the visual-type list could be trimmed—but no sentence is pure waste and the important routing info comes early.

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 being present (so return values needn't be re-explained), the description still usefully summarizes the payload structure and the meaning of the 'next' timeline marker. With annotations covering safety and the schema covering types, the only unpaid bill is the absent locale semantics beyond the enum, which is minor.

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 only 50%—the slug parameter is documented as 'Event slug (per-locale)' and locale is an enum with a default—but the description adds the critical detail that the slug is event-scoped and comes from specific sibling tools. That provenance and per-locale implication go beyond the terse schema, lifting it above the baseline 3.

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 (Fetches) and resource (the explainer for one news event) keyed by a uniquely-identifying parameter (event slug). It distinguishes itself from siblings by noting the slug comes from list_explainers or get_event, and by defining explainer content (question, narration beats, visual data) that separates it from get_event or get_thread.

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 clear context—'Suited to questions about why a story matters'—and names upstream tools that supply the required slug (list_explainers, get_event). It does not explicitly state when NOT to use it (e.g., to use get_event for raw event data), so it stops short of full routing guidance.

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