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

With no annotations, the description carries the burden and does disclose key traits: no sending, no credits consumed, and that passed fields override saved campaign settings. It does not mention permission requirements or rate limiting, and says nothing about what the preview returns (HTML, text, rendered object).

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?

Compact, front-loaded with the core action before the configuration branches. The middle clause ('with the writing rules, tone, Communication Rules or fixed text') is a slightly dense list that costs some readability.

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?

Covers the two main invocation flows but leaves gaps for a 9-parameter, nested-object tool with no output schema: nothing explains the mode enum, the variant/sample structures, or what the rendered preview actually looks like. An agent could call it, but not confidently interpret the result.

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?

Adds real meaning beyond the 67%-covered schema: the campaign_id vs agent_id+prompt relationship, the 'any field you pass overrides them' precedence, and follow_up #k semantics. It leaves mode/variant/fixed-text details to the schema, which is acceptable at this coverage level.

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 ('render the exact email a campaign would send') and scope (first email or follow-up #k), which distinguishes it from the many send/activate siblings. It does not name a specific alternative like preview_agent_email or get_campaign_email, but the 'No sending, no credits' clause makes the non-mutating preview role clear.

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 explicit configuration paths: campaign_id to use saved settings, or agent_id + rules for an unsaved draft, plus the override rule. It doesn't say when to choose this over preview_agent_email or crm_preview_email_to_lead, so the alternative-selection guidance is incomplete.

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