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

Annotations already declare read-only, idempotent, non-destructive behavior, so the safety profile is covered. The description adds genuinely useful context beyond that: the comparison of the range 'against the same number of days just before it' and the connectivity prerequisite. It does not, however, address freshness, sampling, or rate limits.

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?

Two tight sentences: the core capability and comparison behavior lead, followed by prerequisites, safety note, and related tools. No redundancy, every clause carries information.

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 an output schema present, return values need not be spelled out, and annotations carry the safety profile. The description covers the prerequisite, scope, and comparison behavior an agent needs to invoke it correctly.

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 both from/to parameters (including the default of the last 28 settled days) are already fully documented. The description's mention of a date range and comparison period is framing rather than added parameter semantics, so the 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?

States a specific verb (Reports) and resource (Google Analytics organic search sessions, active users, key events, top organic landing pages) with a comparison window. It names related siblings (get_search_performance, get_content_performance) but never explains how this tool differs from them, so it falls short of full sibling differentiation.

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 context: 'Requires a connected Google Analytics property' and 'Does not change anything,' plus points to related tools. However, it never states the condition under which an agent should pick this over get_search_performance or get_content_performance, so there is context but no explicit when/when-not.

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