send_message_to_phone

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

With no annotations provided, the description fully discloses the delivery condition (only if registered), the success/error return messages, and a list of possible exceptions (invalid number, not registered, connection issues, authentication failure, invalid message format). This goes beyond basic operation and gives the agent a realistic expectation of behavior.

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 well-structured with clear Args, Returns, and Raises sections, making it easy to scan. It contains a slight redundancy in the opening sentences but every section adds meaningful information without excessive verbosity.

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 2-parameter tool with no annotations and no schema descriptions, the description is remarkably complete. It covers purpose, parameter semantics, return values, and error conditions, leaving little ambiguity about how to invoke the tool and what to expect.

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?

The schema provides only type strings with no descriptions, so the parameter details in the description are essential. It thoroughly explains 'cellphone' format (international, country code, DDD, no special characters, example) and 'message' content (text, emojis, line breaks), including the specific rule to prepend 55 if missing.

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 it sends a text message to a specific phone number via WhatsApp, using the verb 'Envia' and resource 'mensagem de texto para um número de telefone específico'. It distinguishes from the sibling tool 'send_message_to_group' by emphasizing 'números de telefone individuais'.

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 context that the message will only be delivered if the number is registered on WhatsApp, which is a key usage condition. It also implies the tool is for individual numbers, differentiating it from group messaging, though it does not explicitly name alternatives or state when not to use it.

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