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

Beyond the read-only annotation, the description discloses the source-check order, source-specific null behavior, 404 semantics when an id is unknown to both sources, the cost of one credit, and the deliberate placement of reach data in raw. It also clarifies a subtle field meaning: countries here is ad targeting, not search-market context.

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 dense but front-loaded, starting with what the tool returns and then explaining source resolution. It is somewhat long, but nearly every sentence carries behavioral or semantic information relevant to correct invocation.

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 does a good job explaining the shared Ad shape and source-specific null fields, as well as 404 and reach-field behavior. It is nearly complete, though the undocumented cache_max_age parameter remains a gap.

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?

The description richly explains ad_id as a numeric id or URL from either surface, going beyond the schema's brief note. However, schema coverage is only 50% and cache_max_age is neither described in the schema nor mentioned in the description, leaving one parameter undocumented.

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 resource and retrieval mode: one TikTok ad by id or URL. It also distinguishes this lookup from its dual-source resolution behavior and from broader search semantics, so an agent can identify the correct tool without opening the schema.

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 clearly explains when a URL restricts the query to one surface and when an id triggers the Creative Center-then-Library fallback. The only gap is that it does not explicitly name tiktok_adLibrarySearch as the alternative for discovery rather than direct lookup.

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