send_postcard

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

The description discloses cost ($4.99 per card), delivery time (3-5 business days), and the physical action (robotic handwriting, USPS). It also explains the default-card fallback. Since the annotations only offer basic hints (openWorldHint, non-idempotent, non-destructive), the description carries the behavioral burden well. It does not mention irreversibility or error handling, but the cost and physical nature imply permanence.

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 four sentences with no redundancy. It front-loads the main purpose, then gives operational details (delivery time, cost), then explicit instructions and fallback behavior. Every sentence contributes essential information, making it both concise and well-structured.

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?

With 11 parameters and no output schema, the description covers the core flow and key defaults but leaves out optional parameters like idempotency_key, return_address, and handwriting_style. These are fully documented in the schema, so the description doesn't need to repeat them. However, it does not mention what the tool returns (e.g., a tracking ID), which is a minor gap given the lack of an output schema.

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 baseline is 3. The description adds little beyond a summary: it reminds the agent to provide address, message, and optionally an image, and repeats the 400-char limit already in the schema. It does not enrich parameter meaning beyond the schema's own descriptions.

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 states a specific verb and resource: 'Send a physical handwritten postcard to a US mailing address.' It clearly distinguishes itself from the sibling tool generate_message, which is for creating message content, not sending physical mail. The inclusion of 'physical,' 'robotic handwriting,' and 'USPS' leaves no ambiguity about what the tool does.

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 gives clear context for when to use the tool: when you need to send a physical postcard to a US address. It implies the alternative (generate_message) by focusing on the send action, but it does not explicitly compare against it or state exclusions. The context is unambiguous, but explicit 'when not to use' guidance is missing.

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