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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds value by explaining the content type (statistic/record/anecdote) and that it includes a link to the source note, providing context beyond the annotations. It does not mention any rate limits or authentication, but these are not necessary given the tool's simplicity and 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?

The description is a single, compact sentence that immediately conveys the tool's purpose and output. It is front-loaded with the core concept and contains no redundant information.

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 read-only tool with one well-documented parameter and no output schema, the description adequately explains what the tool returns (a fact with a link) and the source context. It is complete for an agent to call it correctly without needing additional clarification.

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?

The schema provides 100% coverage for the single locale parameter, including its enum values, default, and description. The tool description does not add any parameter-specific detail beyond what the schema already states, so the baseline of 3 is appropriate.

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?

The description clearly states the tool provides the highlighted fact of the day—a statistic, record, or anecdote—drawn from a published note and includes a link to that source. The verb 'get' combined with the resource 'fact_of_the_day' is specific, and the description's content distinguishes it from sibling tools like get_article or get_matches.

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 implicitly signals when to use this tool (when a user asks for the daily fact), but it does not explicitly mention alternatives or exclusion criteria. The name and description make the use case obvious, so the guidance is clear but not explicit.

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