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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds value beyond that by disclosing the return artifact ('a preview link') and the lifecycle position ('before activating'), which tells the agent this is a non-mutating inspection step. It does not mention link expiry, permission requirements, or error behavior for invalid placements.

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 action, the artifact, and the motivation in that order, with no filler. The parenthetical '(or creative)' adds a small amount of ambiguity but also useful flexibility, so it largely earns its place.

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 five-parameter read-only tool with no output schema, the description covers what it returns (a link) and why it is used (pre-activation review). The remaining gaps, namely how folder and account scope the lookup and what happens when a placement is unsupported, are minor for a simple preview call.

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 60%, so the schema already documents folder, account, and language. The description adds only marginal meaning: 'ad (or creative)' hints that the ad parameter accepts a creative reference, and 'given placement' maps loosely to the format enum. It says nothing about the account/folder scoping parameters or valid placement values beyond the enum itself.

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: 'Get a preview link for an ad (or creative) in a given placement'. An agent can distinguish this from meta_ads (listing) or meta_creative_insights (analytics) because the deliverable is explicitly a preview link, not data. It stops short of naming a sibling alternative, so it is clear but not fully differentiated.

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 clause 'so the user can see how it looks before activating' implies the usage context (pre-launch creative review) without stating it as a rule. There is no explicit when-not guidance, no mention of what to do if the ad is already active, and no pointer to alternative preview approaches among the many meta_* siblings.

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