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

Annotations already declare readOnlyHint and destructiveHint, and the description adds substantial behavioral context: response shape, hobby-plan limitations and snippet installation, nested stats placement, units for metrics, and server-time approximation caveats. Nothing contradicts the annotations.

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?

The description is long but dense and front-loaded: purpose first, then response format, then important caveats. There is minor redundancy with the schema's nested stats example, but each section carries meaningful operational detail an agent would otherwise miss.

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 provides a complete response example, field semantics, units, plan behavior, and a precision caveat. For a read-only tool with one optional parameter, everything needed to call and interpret it correctly is present.

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 the baseline is 3; the description adds meaning beyond the schema by explaining metric units, the 'never flat on the site object' nesting rule, and timezone approximation. The date_range parameter itself is already fully documented in the schema, so this enrichment is helpful but not extraordinary.

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 opens with a specific verb and resource: 'List the sites this API key can read.' This clearly distinguishes it from sibling list tools like list_funnels and list_goals, and from create/update site tools. The scope ('this API key can read') removes ambiguity about authorization.

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?

The description gives practical guidance: use site_id with other tools, and use query_stats when timezone-exact numbers are needed. It clearly implies when list_sites is appropriate, though it does not exhaustively enumerate all sibling alternatives.

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