Get ad

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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds genuinely useful non-obvious behavior: it 'Falls back to HTML/list when getAd returns 400,' disclosing an error-handling quirk that the annotations do not capture.

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 short sentences, front-loaded with the core action, then usage routing, then fallback behavior. Most sentences earn their place, though 'Returns the ad card' is mildly redundant given an output schema exists.

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?

Output schema exists, so the description need not explain return values, and it doesn't over-invest there. It covers action, alternative, and failure fallback, which is nearly everything an agent needs for a simple one-param read tool.

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 0% for the single ad_id string, so the description must carry parameter meaning. It implies ad_id is an ad identifier ('by id') but adds no format, type, or validity guidance beyond that, leaving the param thin.

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?

States a specific verb and resource ('Fetch one ad by id with full fields'), and the singular 'one ad' implicitly distinguishes it from the sibling get_ads list tool. The scope ('full fields') is concrete enough that an agent knows what it gets back.

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?

Explicitly routes metrics work to get_ad_stats ('for metrics use `get_ad_stats`') and frames this tool for diagnosis. It gives clear when-to-use context but does not address the other adjacent siblings (get_ads, preview_ad), so it falls just short of fully exhaustive guidance.

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