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

Annotations already indicate readOnlyHint=false (write operation), idempotentHint=false, and openWorldHint=true, so the safety profile is largely covered. The description adds the requirement for authentication via environment variables, which is useful context. However, it does not disclose behaviors such as side effects (e.g., actual SMS delivery), rate limits, or failure handling, so it adds only modest value beyond annotations.

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 a single, concise sentence that front-loads the primary action and includes essential setup information. Every word earns its place, with no redundant or vague content.

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 tool has nested objects, an output schema (not shown but indicated), and annotations. The description covers the basic purpose and environment requirements, but does not mention anything about the array nature of 'to', potential multi-recipient behavior, or the need for pre-approved templates (though the schema mentions 'Approved EngageLab SMS template ID'). With an output schema present, return values need not be described, but the description could still be more complete regarding input prerequisites and behavioral nuances.

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 only 50%, with the outer 'template' object lacking a description, and the tool description does not compensate by explaining the parameters. The schema itself provides descriptions for 'to' and the inner fields of 'template' (id and params), but the description merely mentions 'using a template' without elaborating on required structure or parameter semantics. This leaves gaps that could confuse an agent about how to construct valid inputs.

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 clearly states the action ('Send SMS'), the target system ('EngageLab'), and the method ('using a template'). It is specific and unambiguous, making it easy for an agent to understand what this tool does even without sibling tools for comparison.

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 provides clear context by mentioning the required environment variables (ENGAGELAB_DEV_KEY and ENGAGELAB_DEV_SECRET), which is important for successful invocation. However, it does not explicitly state when to use this tool versus alternatives or provide exclusions, though no sibling tools exist. This gives clear context but no when-not-to-use guidance.

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