Coverage

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), yet the description still adds substantive behavior: the default window is the last 7 days and the queryable range is capped at 90 days, a constraint absent from the schema. Per-day granularity and the 1440-polls-per-day denominator are also disclosed. That is real added context above the 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?

One sentence that front-loads the time scope and then lists outputs in a tight enumerated series; every clause carries content. The opening 'When Tifa was watching' is the one piece of jargon a reader must infer a meaning for.

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?

With no output schema, the description effectively serves as the return-value contract by naming each reported metric, which is exactly what an agent needs to decide whether to call it. It omits pagination/shape details and cost, but for a two-optional-parameter read-only report it is close to sufficient.

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 description coverage is 100%, so the per-field format details (ISO 8601, epoch seconds, London dates) need no repeating. The description nonetheless adds the effective default range (7 days to now) and the 90-day maximum, which the schema does not state. Modest but genuine value beyond the structured fields.

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 enumerates the specific payload: per-source spans, share of range watched, uncovered gaps, and per-UTC-day poll counts (of 1440) and failures. That is far more concrete than the bare name 'coverage'. It never differentiates itself from siblings such as period_stats or current_status, and the phrase 'When Tifa was watching' is unexplained shorthand, so it falls short of a 5.

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 a crisp use condition: 'Check it before reading a quiet period as a good one' – i.e. use this to validate whether silence means no data versus no events. It offers no explicit when-not or named alternative among list_lines/period_stats, so it is clear guidance without exclusions.

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