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

Annotations already declare readOnlyHint=true, so the non-mutating nature is covered. The description adds genuinely useful context beyond that: it requires a Proof account, requires authenticating this client first, and explicitly clarifies that start_login does NOT unlock this tool, preventing a plausible misfire.

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 action in the first sentence, followed by the observed effect on output. The second paragraph is slightly verbose but earns its place by covering the auth prerequisite and the start_login caveat, so no sentence is wasted.

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 return burden and does so conceptually ('shows how the message will look with placeholder variables filled in'), plus it covers the auth prerequisite. For a read-only 7-param preview tool this is close to sufficient, with only the sibling distinction left implicit.

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?

With 100% schema description coverage across all 7 parameters, the schema already documents channel, message_type, body, profile_id and the button fields. The description only adds the general notion of placeholder variables being filled in, conveying no per-parameter syntax or constraints 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 and resource: preview a template with sample data before saving, rendering it as a sub-account would send it. It is clearly distinct from get/list/update/delete_template, though it never names its closest sibling (render_template) to disambiguate the two rendering tools.

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?

The phrase 'before saving' implies the pre-persist use case, and the second paragraph gives a concrete workflow (authenticate, then call again). However, there is no explicit when-not guidance and no routing to render_template, which appears to do a similar rendering job, leaving the agent to infer the boundary.

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