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

Annotations only flag destructiveHint=true, but the description adds substantial behavioral context: real SMS is sent, credits are consumed per message part whether delivered or not, the action cannot be undone, sandbox mode validates and prices without charging, and retries risk duplicate delivery. This aligns with and enriches the destructive hint rather than contradicting it.

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?

Front-loads the critical WRITE/real-SMS/credit warning, then covers sandbox, scheduling, retry safety, and recipient limits in compact sentences. Every clause carries actionable information with no 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?

Given eight parameters, minimal annotations, and no output schema, the description supplies the missing safety, cost, sandbox, scheduling, duplicate-prevention, and scope information needed to invoke the tool correctly. Return values are not required to be explained because no output schema exists and the description points to delivery-report tools for verification.

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 eight parameters, establishing a baseline of 3. The description adds operational meaning beyond the schema by clarifying that sandbox is required and should default to validation mode, and that schedule queues rather than sends, which is useful cross-parameter context.

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 and resource (sends a real SMS to ONE recipient) and distinguishes itself from siblings by explicitly excluding bulk/list sends and naming cancel_scheduled_message and the delivery-report tools.

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 explicit when-to-use guidance: use sandbox=true first unless the user clearly asked to send now, use schedule for later sends, cancel via cancel_scheduled_message, and do not retry on error without checking list_delivery_reports / list_scheduled_messages.

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