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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered by structured data. The description adds the pre-flight positioning value of the call, but says nothing about whether the estimate is a range or a point value, its typical latency, or account/folder resolution behavior when multiple accounts are enabled.

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?

A single front-loaded sentence with no filler; the purpose and the moment of use arrive immediately. It is arguably too terse rather than padded, so brevity is not the issue.

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 is the only place an agent could learn what an "estimate" looks like (a number, a range, a breakdown by placement), and that is absent. For a read-only, open-world lookup with a fully documented schema, it is workable but leaves a real gap around the return value.

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 100%, so all four parameters – including the nested targeting object with its example sub-fields – are already documented. The description names the targeting spec but adds no syntax guidance, example payloads, or constraints for the optional folder/account/language parameters, so it stays at the baseline.

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?

Description pairs a specific verb and resource ("Estimate the audience size") with the input type ("targeting spec"), so an agent knows exactly what the tool returns conceptually. It does not differentiate itself from near-siblings such as linkedin_reach_estimate or google_ads_reach_frequency, though the name prefix carries the platform scoping.

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 gives a timing cue for use ("before creating or changing an ad set"), which is genuine usage context. However, it names no alternatives and no exclusions – it never tells the agent to prefer meta_targeting_search for finding valid targeting options first, or what to do if the spec is rejected.

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