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

Annotations only flag destructive/non-idempotent/open-world, while the description adds the critical real-world consequences: the customer receives it immediately, it cannot be unsent, and it consumes message credits. It also discloses the two write endpoints, which is beyond anything structured data provides.

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?

Four tight sentences with the irreversible/costly nature front-loaded, then addressing, then constraints, then endpoints. The all-caps opener is emphatic but functional; no sentence 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?

Covers irreversibility, credit cost, recipient limits, addressing modes, and endpoints for a high-stakes mutation tool with no output schema. It stops short of describing the response or failure modes (e.g., invalid number), so it is strong but not exhaustive.

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 schema already documents all six parameters including the uuid-vs-phone_number XOR and the optional department. The description restates the addressing modes rather than adding format, validation, or default details beyond the schema, so the baseline of 3 applies.

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?

States a specific verb+resource+scope: sends a real SMS/MMS to exactly one contact from the user's Textline number. It is immediately distinguishable from siblings like textline_create_customer, textline_resolve_conversation, and textline_transfer_conversation without opening any 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?

Gives concrete addressing guidance (conversation_uuid OR phone_number + optional department) and clear exclusions: 'One recipient per call; no bulk sends,' plus a pre-send confirmation step. It does not name a sibling alternative, but the constraints are unambiguous.

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