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

Goes beyond annotations by disclosing that it publishes to a real person's inbox, the 24-hour window constraint, and Instagram's Advanced Access requirement. Annotations already indicate write operation (not read-only) but description adds crucial failure 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?

Well-structured with main action first, then safety warning, then constraints, then Instagram specifics. Every sentence adds value, though it could be slightly more concise; still efficient for the information density.

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?

Thorough coverage of a complex tool (two channels, permissions, time windows, failure modes) despite no output schema. Addresses all necessary context for an agent to use safely and correctly.

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?

Adds value beyond 100% schema coverage by explaining how to obtain recipient_id (from get_conversation or list_comments) and implying mutual exclusivity of text and image_url. Schema descriptions are present but description provides practical sourcing and usage 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?

Clearly states the action (send), the resource (direct message), and the channels (Messenger or Instagram Direct). Distinguishes from siblings like private_reply and comment-related tools by explicitly saying 'Instagram comments are NOT affected.'

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 (within 24-hour window), when-not-to-use (outside window requires message tag or paid channel), and safety advice (confirm with human). Also details Instagram Direct permissions and failure mode (timeout, subcode).

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