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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is known. The description adds the cost implication ('Spends a credit or two') and the return format (compact JSON with listed fields), which goes beyond annotations. This adds useful behavioral context without redundancy.

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 two sentences with zero filler. It front-loads the core purpose and usage, then adds the alternative and cost note. Every sentence earns its place, making it highly efficient.

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?

For a read-only search tool with 7 parameters all documented in the schema, the description covers the essential aspects: when to use, return structure, and cost. It does not mention pagination or edge cases, but the schema's limit description covers max returns and default. Overall, it is sufficiently complete for an agent to call it correctly.

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 every parameter is already documented in the schema. The description restates the mutual exclusivity of query vs. companyName/pageId, but that is already implied in the schema descriptions (e.g., 'use INSTEAD of companyName/pageId'). The description does not add meaningful new meaning beyond what the schema provides, so a 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 states a specific verb and resource: 'Structured Meta Ad Library pull'. It clearly defines the scope as fetching ads by keyword (query) or advertiser (companyName/pageId), distinguishing it from generic research. This is specific and unambiguous, and the contrast with research_ads in the same sentence reinforces the clarity.

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 explicitly states when to use: 'use when you know exactly WHAT to fetch', and gives the alternative for open-ended research: 'use research_ads instead'. This provides clear usage context and a named alternative, leaving no ambiguity about selection criteria.

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