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

Annotations only say readOnlyHint=false and destructiveHint=false, which are minimal. The description adds meaningful behavioral context beyond them: the tool 'costs credits' and the same keyword set re-queried within a week is free. This discloses cost/quota impact and caching behavior that the annotations do not convey, which is exactly the kind of trait an agent needs before invoking a non-read-only tool.

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, roughly 65 words, with the core purpose front-loaded in the first sentence. The second sentence handles usage triggers, and the third covers parameter behavior plus cost/caching. Every sentence earns its place with zero redundancy.

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?

Even though there is no output schema, the description enumerates the returned data points (monthly search volume, CPC, competition, 12-month trend), so an agent knows what to expect. Combined with fully documented parameters, credit-cost disclosure, free re-query policy, and max-keyword constraint, nothing essential is missing for correct invocation.

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% with rich descriptions already, including example values for keywords and specific market codes for location_code. The description adds only marginal value by restating the omit-for-worldwide behavior and clarifying that a market code targets one country. Given the high schema coverage, baseline 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 a specific action and resource: retrieving 'Google Ads (Keyword Planner) monthly search volume, CPC, competition and 12-month trend'. This is a specific verb+resource with concrete metrics and constraints (up to 10 keywords, one call). It clearly differentiates from siblings like research_backlinks and research_competitors by focusing on keyword search metrics rather than link or competitor analysis.

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 explicit when-to-use guidance: 'Use when the user asks how often something is searched, or to size a keyword before writing a page.' This establishes clear context for invocation. However, it does not name alternatives or state when-not-to-use, which keeps it a step below full routing clarity.

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