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

No annotations are provided, so the description carries the full burden. It discloses that the tool sends a message and returns a message_id, and it mentions the max length. However, it does not mention side effects (e.g., costs), error conditions, delivery guarantees, or any permission requirements. For a write operation, this is a moderate level of transparency, but not comprehensive.

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 short, with three sentences that each add value: purpose, format constraint, and return value. It is front-loaded with the primary action. It contains slight redundancy with the schema (max length and phone format), but it's still efficient and easy to parse.

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 is simple (3 params, no nested objects, no output schema). The description covers the essential behavior (send, return id), format constraints, and a concrete example. It lacks information on error handling or delivery implications, but for a straightforward send operation, this is adequate. No annotations exist to supplement, but the description covers the core needs.

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 parameters. The description repeats the phone-number format and max length that are already in the schema, adding no new semantic value. It provides a concrete example (420777123456) that is also in the schema, so no additional compensation is needed.

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 specific action and resource: 'Send an SMS message to a phone number via SmsManager.cz.' It also mentions the return value (message_id), making the tool's purpose unambiguous. No sibling tools exist, so differentiation isn't required.

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: it's for sending SMS messages, and it explicitly notes the phone number format and character limit. There are no alternatives listed, so no explicit exclusions are needed. It implicitly tells the agent when to use it, and the constraints are practical.

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