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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the extra value here is the disclosure of return contents and the failure mode ('an error when the ad is inaccessible'). It doesn't mention rate limits, partial results, or behavior with multiple comma-separated IDs, keeping it below 5.

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 verb and resource, then returns, then the disambiguating scope note. No filler or repetition of the title.

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 single-parameter read with no output schema, the description does the necessary work by naming the returned fields and the error case. Minor gaps remain around multi-ID batch behavior and whether missing fields are omitted or null, but nothing critical to invoking it is absent.

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% and the schema already spells out both accepted forms (single integer or comma-separated string with an example). The description only says 'by ID' and adds no syntax, batch-size, or ordering guidance beyond the schema, so baseline 3 applies.

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 ('Read an advertising-library ad by ID') and enumerates what comes back (configuration, content, creative references, channel, status). It also fences itself off from analytics tools by noting it is an 'ad definition, not an experiment performance report,' though it doesn't name the nearest siblings like search_ads_by_names or fetch_creative_details.

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?

Usage is implied rather than stated: the agent can infer this is the ID-based lookup path and not a performance report. There is no explicit 'use this when you have IDs, use search_ads_by_names when you only have names' routing, and no stated prerequisites or exclusions.

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