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

With no annotations, the description carries the full burden of behavioral disclosure. It does disclose an access prerequisite and the return behavior, but it does not state whether rendering is side-effect-free, how missing variables are handled, or whether anything is sent or persisted. The word 'Render' implies a read-like operation, but it is not made explicit.

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 short, front-loaded with the core purpose, and every sentence earns its place. The return value is stated in the first line, and the access note is compact yet specific.

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?

The description is incomplete for a tool with no output schema and no annotations. It explains return value and access, but it leaves critical call-time information undocumented: valid message_type values, how the template is selected, and what happens when variables are missing or incomplete. An agent cannot confidently construct correct input from this description alone.

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 the structured schema already documents channel, message_type, and each variable key. The description adds only generic phrasing ('provided variables') and no additional parameter meaning, which matches the baseline of 3.

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 ('Render') with a specific resource ('a template') and explicitly says what it returns ('fully rendered message content'). It is understandable in isolation, but it does not differentiate from closely related siblings such as preview_template or render_auth_link.

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 description gives actionable access guidance ('needs a Proof account', authenticate then call again, 'start_login does NOT open this tool'), which helps the agent sequence the call correctly. However, it never explains when to use render_template versus preview_template or render_auth_link, so the choice among sibling tools is left implicit.

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