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

Annotations only say readOnlyHint=false and idempotentHint=false; the description adds the important non-obvious behavior: it sends one real text per number, returns per-number Twilio errors, and 'success' only means Twilio accepted, not delivered, due to carrier filtering of unregistered US senders. It also points to a doc resource for error codes, which annotations cannot convey.

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 action and prerequisite, and every sentence contributes distinct information (preconditions, return shape, success semantics, doc pointer, sibling exclusion). It is slightly dense at five sentences, but nothing is filler.

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?

No output schema exists, yet the description describes the return value (per-number results with Twilio errors) and the success caveat. With one 100%-covered parameter and explicit preconditions, an agent has everything needed to call it and interpret the result.

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% and the single project_id parameter is already fully documented with a format and source tools (list_projects, create_project, bootstrap_site). The description only indirectly references the parameter via 'the project's numbers' and adds no new syntax or sourcing guidance, so the schema does the heavy lifting.

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 names a specific verb (send one test text), the exact resource (each of the project's numbers via the team's Twilio account), and explicitly distinguishes itself from the sibling test_webhook. An agent can tell what it does without opening the schema.

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?

It gives an explicit precondition ('Use after setting notify_phones'), failure conditions (no Twilio account, no notify_phones), and a named alternative with the exclusion ('Do not use this to test email or the webhook — call test_webhook'). This is the when/when-not/alternatives pattern at full strength.

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