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

Annotations only say readOnlyHint=true; the description goes well beyond by describing the return shape (byPlatform[platformId].ready and .missing), how each ad type is represented (text, post, card with title/body/destinationUrl/imageUrl and signed previewUrl), and the rule for when a card format is ready. It also discloses Space scoping semantics and how to override them, which is exactly the kind of context annotations cannot convey.

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?

Front-loaded with the core outcome (how each ad renders on every platform) before type-by-type detail and scoping. Dense rather than padded, though the em-dash-heavy enumeration of ad formats is the longest portion and could be tightened slightly.

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?

There is no output schema, so the description carries the burden of explaining return values, and it does: readiness flags, missing-media signals, per-type rendering, and signed preview URLs. Combined with Space-scoping guidance, an agent has everything needed to interpret the response and act on gaps.

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% and the single-line space_id description already explains the override behavior, so the description's Space discussion largely restates the schema. campaign_id is not elaborated beyond 'the campaign to preview', which the schema already says. Baseline 3 is appropriate when the schema does the work.

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 (preview) and resource (campaign ads) and immediately specifies scope: rendering per platform, compiled exactly as a sync would send it. It is clearly distinct from get_campaign (fetch data) and preview_sync_plan (plan-level preview) because it names the per-ad, per-platform rendering output explicitly.

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?

Gives clear context for when to reach for it (checking per-platform rendering and media readiness before a sync) and points to the concrete remediation path 'attach_asset_to_ad' when media is missing. It does not explicitly contrast with the sibling preview_sync_plan, which is the main alternative an agent might confuse this with, so it falls short of a 5.

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