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

Annotations already declare destructive=true, idempotent=true, and openWorld=true, so the description is not the sole source of safety signals. It still adds real value beyond them: the blacklist is auto-created on first use, changes are mirrored to the ad network only best-effort (so remote state may diverge), and there is a 100-site cap. It does not say whether partial failures are reported, which keeps it from a 5.

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 tight paragraph with the resource and scope front-loaded, then the two behavioral facts an agent needs (auto-created blacklist, best-effort mirroring) and the limit. No sentence is filler.

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 two-parameter mutation tool with strong annotations and no output schema, the description supplies the key operational caveats: API-only scope, auto-created blacklist, best-effort network sync, and the 100-item limit. Only the outcome/failure behavior after a call is left unspecified.

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%, so both parameters are already documented, and the 100-item cap is repeated from maxItems. The description's only added nuance is clarifying that 'sites' means placement/source ids, which is marginal beyond the schema.

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 (block) and resource (placements/source ids) with a clear scope restriction to API-type campaigns, which separates it from the sibling unblock_campaign_placement. It does not name or contrast with that sibling or get_campaign_blacklist explicitly, so it falls short of the top mark.

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 by the verb and the 'API-type campaign' qualifier; the description never says when to prefer this over unblock_campaign_placement or when to check get_campaign_blacklist first. An agent can infer intent but gets no explicit when/when-not guidance.

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