Yandex Metrika: compare periods

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

Annotations already declare read-only, idempotent, non-destructive and open-world, so safety is covered. The description adds real behavior beyond them: identical-conditions requirement for comparability, null percent on a zero baseline, percentage points for rate metrics, quota consumption with cache fallback, and an explicit prompt-injection warning about labels being external data.

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 comparison semantics and no filler sentences; each clause carries content (default period, null-percent edge case, quota, injection safety). The semicolon-chained density makes it slightly harder to scan than a bulleted structure would be.

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 an 11-parameter nested tool with an output schema, the description covers comparison semantics, defaults, edge cases, quota behavior and safety, which is what an agent needs before calling. The only meaningful gap is explicit sibling differentiation against the report and timeseries tools.

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%, so the bar is the baseline 3, and the description does add meaning: it explains that dimensions produce per-segment comparisons and restates the default period pair, which governs how the periods object should be left unset. It still does not explain the interaction between preset and goal_ids beyond what schema text says.

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: 'Compares Yandex Metrika traffic between two periods'. It also names the comparison outputs (baseline, current, absolute and percent change, percentage points) and contrasts the mode with per-segment comparison via optional dimensions, which separates it from metrika_run_report and metrika_run_timeseries.

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 operating guidance: same counter/metrics/filters/time zone for a valid comparison, default period pair, and an explicit caution not to loop calls because they spend API quota (with cache caveat). It does not explicitly say when to prefer this over metrika_run_report or metrika_run_timeseries, so the sibling routing is inferred rather than stated.

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