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

Annotations already declare this as a read-only, idempotent, non-destructive operation. The description adds valuable behavioral context beyond annotations: nothing is sent or saved, and unknown placeholders render empty rather than failing, which is non-obvious and important for interpreting preview results.

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?

The description is tightly written and front-loads the primary purpose. Every sentence carries useful information: the preview behavior, the safety/failure semantics, and the alternative tools.

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 simple two-parameter, read-only preview tool with full schema coverage and annotations, the description is complete enough. It explains what the agent will see and why it is safe, and it routes adjacent work to the correct siblings.

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 `campaignId` and `message` are already documented in the input schema. The description adds some useful context about placeholder resolution and using a real lead, but does not provide additional parameter syntax or format details 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?

The description states a specific verb and resource: render a draft message against a real campaign lead to inspect merge-field resolution. It also distinguishes the preview action from saving via `flow_set` and from sending a test email via `campaign_send_test_email`.

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?

It gives explicit when-to-use guidance: check the copy before committing it to a step. It also names the alternatives for adjacent tasks, `flow_set` for saving and `campaign_send_test_email` for putting a real email in front of the user.

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