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

Annotations declare the mutation profile (readOnlyHint=false, destructiveHint=true, idempotentHint=false), and the description adds rich context beyond them: it auto-creates/reuses a chat, is hard-limited to one reply per comment ever, bypasses the 24h window, and omits media attachments. These are exactly the operational traits an agent needs before calling a write tool.

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 purpose in the first clause, then layers constraints and interactive-element behavior. It is dense but nearly every clause carries a distinct, decision-relevant fact; only the dm_message_send parity sentence is arguably redundant.

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 mutation tool with no output schema and seven parameters, the description covers the platform scope, the one-shot constraint, window bypass, and how postback taps surface as inbound messages. An agent has everything needed to call it correctly and anticipate the side effects.

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 coverage is 100%, so the baseline is 3, but the description adds cross-parameter constraints not encoded in the schema: text is capped at 80 characters when buttons are present, media is unavailable, and quick replies cannot be combined with buttons on Instagram. This meaningfully extends what the schema alone conveys.

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 precise verb+resource ('Send a DM to the author of a comment, in reply to that comment') and names the Meta concept ('Private Replies'). The scope ('Instagram and Facebook (Page comments) only') and the implicit contrast with dm_message_send, which it references for interactive-element parity, let an agent place it correctly among siblings.

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 strong usage context: bypasses the 24h window for comments up to 7 days old, one private reply per comment ever, and platform limits. It references dm_message_send but only for feature parity, not as an explicit 'use that instead when X' routing rule, so it stops just short of full when/when-not guidance.

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