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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely non-obvious behavior beyond that: a segment is app-wide regardless of the platform it was created on (madeOn records origin), and size/people are computed relative to the platforms requested. It omits pagination and result-limit behavior, which keeps it from a 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 tight sentences with the resource definition front-loaded and no filler. The later sentences shift from what the tool returns to how fields are computed, which is dense but earns its place given there is no output schema.

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, zero-required-parameter list tool with no output schema, the description usefully pre-explains the key return fields (size, people, madeOn). However, it never addresses result volume, ordering, or the appId/productId fallback rules, leaving meaningful gaps for an agent deciding how to call it.

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 the baseline is 3 and the schema already documents appId, platforms, and productId in detail. The description adds one useful link — that requested platforms scope the size/people counts — but does not clarify the appId-versus-productId relationship, which is the most ambiguous part of the schema.

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 opens with a concrete resource definition — "Saved audiences of an app, with their filters and current size" — which lets an agent recognize segments as saved-audience objects distinct from subscribers, ratings, or notifications in the sibling list. The listing verb is only implied (the tool name carries it), and no sibling is named as an alternative, so it stops short of a 5.

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?

There is no statement of when to call this versus alternatives — notably estimate_audience, which is the obvious sibling for audience-size questions. The text explains how segment size is computed across platforms, but that is semantics, not usage routing; an agent must infer the selection criteria itself.

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