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

No annotations are provided, so the description carries the behavioral disclosure burden. It does reveal that the tool returns real-time delivery status, segments, and cost, which is useful. However, it does not mention error behavior, whether the operation is read-only, or what happens when a message ID is invalid or not found.

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 sentence with no filler. Every word contributes meaning: real-time, delivery status, segments, cost, and the ID-based lookup.

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 single-parameter getter with no output schema, the description gives a solid outline of what the agent will get back: status, segments, and cost. It is concise and complete enough for typical use, though error or not-found behavior is not described.

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%, and the message_id parameter is already explained as the ID returned by send_sms. The description adds only the general 'by ID' phrasing, so it does not need to compensate for missing schema information.

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 uses a specific verb ('Check') with a clear resource: delivery status, segments, and cost of a sent message by ID. This distinguishes it from siblings like list_messages or get_analytics, which cover different query scopes.

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 'by ID' and the schema's reference to 'Message ID returned by send_sms' make the intended usage context clear. It does not explicitly list alternatives or exclusions, but the context is sufficient for a simple getter tool.

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