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

Annotations cover the safety profile (destructiveHint=true, idempotentHint=true, openWorldHint=true), so the bar is lower. The description adds things annotations can't express: no email is sent, a paid account is required, and 'set who a campaign will go to' signals replacement of the existing recipient list, which explains the destructiveHint. It doesn't spell out what happens to a previously assigned list explicitly.

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?

One compressed paragraph, front-loaded with 'WRITE:' as a signal token, then scope, then behavioral caveats. Every clause carries information; nothing is padded.

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 mutation tool with no output schema, the description supplies the essentials: write nature, audience options, no-send guarantee, paid-account prerequisite. Minor gaps remain around campaign-state prerequisites and how an existing recipient list is treated on re-assignment.

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 75% and the schema already documents match_type's OR/AND semantics and the subcategory_ids conditional requirement. The description's restatement of match_type ('any = OR, all = AND') duplicates schema content and it says nothing about campaign_id, so it adds little beyond the structured fields.

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?

Opens with a specific verb and resource ('WRITE: set who a campaign will go to') and immediately scopes the two audience modes. It explicitly distinguishes itself from the send path with 'Does not send anything', separating it from sibling enginemailer_send_campaign.

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?

'Does not send anything' implicitly routes the agent to send_campaign for the actual send and positions this as the configuration step. It doesn't state ordering or prerequisites beyond the paid-account requirement (e.g., whether the campaign must exist first), so a 4 rather than a 5.

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