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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds meaningful behavioral scope by enumerating exactly what the comparison returns (totals, devices, moved pages/queries, matching-property GA sessions, in-window Google updates), which the annotations cannot convey.

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 operation, and the follow-up sentence handles the optional parameter. The first sentence is dense with comma-separated output clauses but each clause carries information, so there is no obvious waste.

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 appropriately shoulders the burden by describing the return contents, and it covers all three parameters plus the triggering context. It omits pagination/format details but nothing critical for correct invocation is missing.

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 baseline is 3. The description goes beyond the schema by clarifying 'pages' semantics for filtering ('narrows it to URLs that contain that text, such as /blog/'), which adds interpretation value on top of the schema's 'Optional URL text' wording.

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: it 'compares equal periods before and after a date' and enumerates the outputs (totals, devices, moved pages/queries, GA sessions, Google updates). The comparison operation is distinctive, but no sibling (e.g., seo_data or seo_report) is named, so the differentiation is implied rather than explicit.

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 concrete triggering contexts ('a site change or a Google update'), which tells the agent when this tool is the right choice. It stops short of naming an alternative tool or stating when not to use it, so it does not reach the 5 level.

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