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

readOnlyHint=true already tells the agent this is a safe read; the description adds that results are scoped to a single link and derived from visit firing data, which is real context. It does not mention whether an empty result means no pixels or an unconfigured link, nor any result ordering or limits.

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 the purpose stated before the parameter clause, and the platform parenthetical earns its place by defining output scope. Slightly dense, but no wasted sentences.

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 one-parameter read tool with no output schema, the description is sufficient: it names the platforms returned and the input that drives the result. Only the empty-result / not-configured semantics are left unaddressed, a minor 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?

Only one parameter and schema coverage is 100%, with the schema saying 'The link to check.' The description's 'given its link_id' reinforces which identifier is expected but adds no format or sourcing detail beyond the schema. 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 (list), resource (retargeting pixels) and scope (that fire on a link's visits, given link_id), and enumerates the pixel platforms returned. This clearly separates it from retargeting_pixels_get and retargeting_pixels_update, which operate on pixel configuration rather than per-link firing.

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?

The phrasing 'that fire on a link's visits' implies the diagnostic use case, but there is no explicit when-to-use, no prerequisites, and no reference to sibling tools such as retargeting_pixels_get for pixel-level configuration. Usage is inferable rather than stated.

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