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

Annotations already indicate readOnly=false and idempotentHint=true. Description adds two useful behaviors: links are removed and recipient is told an assistant sent it. This goes beyond annotations without contradicting them.

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?

Two sentences with zero redundancy. Front-loaded with the core action, then usage condition, then behavioral notes. Every sentence adds value.

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 messaging tool with no output schema, the description covers key operational details: sender identity, recipient, use case, and content transformations. Missing error/rate-limit info but not critical for basic invocation.

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 has 100% description coverage, including descriptions for listing_id, message, and idempotency_key. The tool description adds no new parameter-specific meaning beyond what the schema already provides, so baseline of 3 is appropriate.

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?

Description states a specific action (send message) with a clear target (landlord of a rental) and actor (signed-in person). It distinguishes itself from siblings by noting it's for questions a listing doesn't answer, setting it apart from request_tour or start_application.

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 condition for use: 'Use for questions a listing does not answer.' This implies when to use, but doesn't explicitly mention alternatives like request_tour for tours or start_application for applications, though those are implicitly different. Clear enough for routing.

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