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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds useful behavioral context beyond annotations by disclosing plan-based history limits: 30 days on Free and 365 days on Unlimited. It repeats 'Read-only' but does not contradict 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?

Three sentences, front-loaded with the core return value and optional competitor scope. The plan-limit sentence earns its place by communicating a real constraint, and the final 'Read-only' note is short despite duplicating an annotation.

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?

The tool has an output schema for return shape and rich annotations for safety behavior. The input schema fully documents both parameters, and the description adds the important plan-based history-window constraint. Nothing essential 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 description coverage is 100%, so both parameters are already well documented. The description adds limited semantic context by clarifying that appId is optionally for a competitor app, but it does not provide meaning beyond what the schema already supplies for trackedKeywordId.

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 states a specific verb and resource: returns rank history for one tracked keyword, optionally for a competitor app. This is clearly distinct from sibling list_keywords and list_keyword_competitors, which manage or list keywords rather than return historical rank data.

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?

It gives clear context for when the tool applies: retrieving rank history for a single tracked keyword, with an optional competitor app. It does not explicitly name alternatives or when-not conditions, but the intended usage is unambiguous.

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