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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds valuable non-redundant context: only counts are returned, and no IP addresses or user agents are stored, which sets correct expectations about output and privacy.

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-loads purpose, then illustrates with compact examples, then closes with output and privacy caveats. Every sentence carries information and nothing is padded.

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 compensates by stating that only counts are returned and that no IPs/user agents exist, and the examples cover the filter-plus-group idiom end to end. All 12 parameters are schema-documented, so the description does not need to repeat them.

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 schema establishes the baseline. The description goes beyond it by showing parameters in realistic conjunctions (os=iOS + country=US; group_by=source) that convey how filters compose, which is real added meaning rather than restatement.

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: count pageviews/custom events and unique visitors matching filters, with optional grouping. The four concrete examples (iOS+US, Firefox by source, signups per country, /pricing per day) make the tool's reach unambiguous. It does not explicitly distinguish itself from overlapping siblings like top_pages, top_countries, or top_browsers, which the examples actually overlap with, so it stops 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?

Four worked examples give clear contextual guidance on how to combine filters and group_by for real questions, which is strong 'when to use' signaling. However, no exclusions or named alternatives are given, leaving the agent to infer when to prefer this over the preset top_* tools.

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