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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true), so the bar is lower. The description adds genuine behavioral context beyond them: the 24-hour reply restriction on Instagram and Messenger and the platform scope. It omits rate limits or failure behavior, but the 24h constraint is a valuable disclosure.

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?

Three tight sentences, front-loaded with the action and platforms, then the constraint, then the ID sourcing. Every sentence carries distinct 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?

No output schema exists, and the description doesn't describe the return value, but annotations cover safety and the schema fully documents all five parameters. For a send tool the remaining gap (response shape, attachments) is minor, leaving it nearly complete.

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 relational meaning beyond the schema by specifying that conversationId and/or participantId come from list_conversations and that at least one is needed, clarifying how the ID parameters combine.

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 ('Send a direct message reply') and enumerates the target platforms (Messenger, Instagram, X). This implicitly separates it from siblings like reply_to_comment and create_post, though it never names an alternative explicitly.

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?

Gives clear entry context: use accountId plus conversationId and/or participantId from list_conversations, and notes the platform-specific 24-hour reply window. It lacks explicit when-not-to-use guidance (e.g., outside the 24h window or for comments vs DMs), so it stops 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.