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

Annotations already cover safety (readOnly, idempotent, closed-world), so the description's added value is the substance: it discloses the result content (distance remaining, 'how far off they are') and the population filter ('Active drivers'). The main undisclosed trait is what threshold counts as 'close', which materially changes result size.

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?

One compact sentence that front-loads the population and the milestone concept before the return content. The trailing clause 'with how far off they are' is slightly awkward but earns its place by describing the output.

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 single-parameter, read-only tool this is close to sufficient, and annotations plus schema carry most of the load. However, with no output schema the description should clarify what a result record contains (driver, milestone type, remaining count) and roughly what 'close' means; both are left to inference.

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 single parameter already documents the slug format, the pattern constraint, and the omit-for-all behavior. The description adds only an indirect hint that omitting the driver yields 'every milestone that is close', which is essentially a restatement of 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?

The description names the resource precisely ('career milestone ... or an all-time team record') and the population ('active drivers'), with a concrete example ('100th podium') that makes the concept unambiguous. It implicitly separates itself from get_record (actual records) by focusing on proximity rather than the record itself, though it never names a sibling.

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?

Usage is only implied: the phrase 'close to' signals the tool is for forward-looking/preview questions rather than lookups. It gives no explicit when-to-use versus get_record or peak_finder, and no statement that it excludes retired drivers or historical retrospective queries beyond the word 'Active'.

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