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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is fully covered. The description adds the useful fact that last-fired timing is returned, but says nothing about pagination, result caps, or what happens when an account has no pixels. With annotations carrying the safety burden, a 3 is appropriate.

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 sentences: the first front-loads what the tool does, the second explains the practical reason to call it. No filler, no restatement 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 one-parameter read tool with rich annotations, the description covers what is returned (pixels plus last-fired time) and the business context for calling it. The only minor gap is workflow placement — it doesn't say this is typically a precursor step to meta_create_ad_set — but nothing needed to invoke it correctly is missing.

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 single parameter's description already points to 'act_...' from meta_list_accounts. The description adds no format, scoping, or validation detail beyond the schema, so this is the baseline case rather than a value-add.

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 ('List a Meta ad account's pixels') plus a scope detail ('when each last fired'). This clearly separates it from siblings like meta_list_accounts, meta_list_pages, or meta_insights without needing the schema opened.

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 second sentence supplies concrete context for when this tool matters: choosing a pixel whose Lead event fires on the client's thank-you page for a website-leads ad set. That's clear situational guidance, but there is no explicit exclusion or named sibling alternative (e.g., when to inspect events instead).

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