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

The description explicitly states this tool MODIFIES live data and consumes message credits, adding clear behavioral context beyond the destructiveHint annotation. It accurately informs the agent that this is a real-world action with cost implications.

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 two sentences long with no wasted words. The first sentence is strong and front-loaded. The second sentence packs REST details cleanly, though could be slightly restructured for 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?

The description lacks information about the return value or success/failure behavior. Since there is no output schema, the agent is left guessing the response format. For a mutation tool with credit consumption, explaining the response would improve completeness.

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 100% with detailed descriptions for each parameter. The description lists the parameters in REST format but does not add new semantic information beyond what the schema already provides. It reinforces optionality (?) but adds marginal value.

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 starts with 'SENDS A REAL SMS or MMS' which is a specific verb+resource combination. The title 'Send message' and context clearly distinguish this from sibling tools like evaluate_message or get_message.

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 advises to 'Provide only the optional fields you need' but does not explicitly state when to use this tool versus alternatives like evaluate_message or when not to use it. Usage context is implied but not contrasted with siblings.

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