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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real context beyond that: results are per-day, the window is bounded to 7–90 days, and a previous-period average position is included for comparison. It says nothing about how the 'potential traffic' figure is derived or how the window interacts with the limit parameter.

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?

A single sentence that front-loads the metrics list, followed by the window and comparison qualifier. No filler, though the metric enumeration plus the parenthetical range makes it dense enough that the prior-period detail could be its own clause.

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 carries the burden of explaining results, and it does list the returned metrics and their daily granularity. However, it never resolves the tension between a 90-day window and `limit` defaulting to 25 rows, nor does it explain what 'potential traffic' means. For a data-retrieval tool with three optional parameters this is adequate but leaves a real ambiguity.

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 `days`, `limit` and `project_id` are already fully documented in the schema, including defaults and ranges. The description only restates the 7–90 range and adds the notion of a prior comparison period, which is not required for correct invocation. Baseline 3 applies.

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 exact metrics returned (clicks, impressions, average position, potential traffic) and the shape of the result (daily, over the last N days), so an agent can tell this is a time-series metrics tool rather than a top-N listing. It does not differentiate itself from siblings like gsc_top_pages, gsc_coverage or gsc_opportunities, leaving the agent to infer that this is the only per-day trend tool.

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?

There is no statement of when to call this versus the many adjacent GSC tools (gsc_top_queries, gsc_top_pages, gsc_opportunities, gsc_impact). The only implicit guidance is the 7–90 day window, which is a constraint, not a usage rule.

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