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

The description goes beyond the annotations (openWorldHint, destructiveHint) by disclosing delivery speed, lack of telecom requirements, and the payment flow via Bitcoin Lightning. It also adds the critical matching constraint between create_payment and send_sms. The schema further notes international one-way behavior, but the description still adds substantial behavioral context.

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 three sentences, front-loaded with the main purpose, followed by key features and the payment dependency. Every sentence adds essential information without unnecessary elaboration or repetition of schema details.

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 description covers purpose, prerequisites, payment method, and global reach. With no output schema, it would be helpful to state what the agent receives after sending (e.g., confirmation ID), but the detailed schema notes for phoneNumber mitigate this gap. Overall, it is sufficiently complete for an SMS-sending tool.

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 input schema already describes all three parameters in detail (100% coverage). The description adds value by emphasizing that phoneNumber and message must match those used in create_payment, which is not stated in the schema. This extra nuance justifies above-baseline score.

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 tool's purpose: to reach a human via SMS for real-world coordination. It uses specific verbs ('send', 'reach') and distinguishes from sibling tools like send_email and send_fax by focusing on SMS and global reach.

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?

Provides clear context for when to use ('when your task requires real-world coordination') and explains the prerequisite of creating a payment via create_payment. However, it does not explicitly mention alternatives or when not to use it, so it falls short of a 5.

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