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

Annotations already mark the tool read-only, and the description adds useful behavioral context about the kind of analysis performed: statistical unusualness, referrer surges, first-time referrers, and share-of-traffic jumps. It discloses the summarization behavior without contradicting the readOnlyHint.

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 a compact, front-loaded summary with a concrete list of what the tool surfaces. The trailing 'period: 7d default' is slightly redundant with the schema, but the overall size is appropriate.

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?

Given an output schema and fully documented parameters, the description is sufficient for an agent to know what this tool returns and when to call it. It could be more complete with explicit sibling guidance, but nothing essential appears 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 description coverage is 100%, so the schema already documents both parameters. The description only repeats the period default and adds no new parameter semantics beyond what the schema provides; the baseline of 3 is appropriate.

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 resource (notable movements in a period) and spells out concrete output categories: unusual traffic days, referrer surges, first-time referrers, pages with jumped share, and recorded annotations. It does not use an explicit verb and does not call out a sibling differentiation, so it stops short of 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?

The phrase 'without scanning raw numbers' gives the agent clear context for when this digest-style tool is appropriate versus looking at raw data. It does not explicitly name alternatives or state when not to use it, but the intended use case is reasonably clear.

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