List pixels

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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=true), so the description's job is to add context — and it does by disclosing a specific failure mode: a 404 means pixel management is not enabled for the account. That is non-obvious, actionable error semantics an agent could not get from structured fields. It stops short of noting result volume or pagination.

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?

Two short sentences, front-loaded with the resource definition and followed by the error condition. Every clause carries information; nothing is redundant with the title or annotations.

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 parameterless, read-only listing tool with no output schema, the description supplies the entity meaning, the key return field, and a notable error case. The only omission is any hint about the shape or size of the returned list, which is minor here.

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?

There are zero input parameters, so the baseline is 4 and there is no parameter meaning to explain. The phrase 'of the ad account' usefully signals that scope comes from the authenticated account rather than an argument.

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 names a concrete resource ('Conversion data sources (web pixels) of the ad account') and clarifies what is returned ('with their pixel_id'), which is unambiguous and goes beyond the bare name. It does not explicitly differentiate itself from siblings like list_conversion_event_settings, though the domain terminology makes the distinction reasonably inferable.

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 only implied: an agent can infer this is the way to discover pixel_id values, but the description never states when to call it versus alternatives or what the prerequisites are. No explicit when-not guidance is given, which is acceptable for a zero-argument read tool but leaves a gap.

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