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

Annotations already declare readOnlyHint=false, destructiveHint=true and openWorldHint=true, so the mutation profile is known; the description adds genuinely new behavioral facts — that replies to DM threads older than 7 days are rejected outright, and the per-platform attachment ceiling. It does not spell out the consequence of destructiveHint (the reply becomes publicly visible on the post, and there is no delete path mentioned here), which is the main remaining gap for 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?

Four sentences, front-loaded with the verb and scope, then sequencing constraint, then platform caveats. Each sentence adds a distinct fact — sibling routing, DM window, no-window platforms, attachment ceiling — with no restated boilerplate.

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 5-parameter write tool with no output schema, the description covers the essentials: where the required id comes from, which platforms are gated by a time window, and what payload limits exist. Remaining details (attachment structure, idempotency window, workspace auto-resolution) are fully carried by the rich schema, so nothing an agent needs is missing.

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 every parameter — body, attachments, workspace_id, conversation_id, idempotency_key — is already documented in the schema, including attachment ordering and idempotency retry semantics. The description's only parameter-adjacent contribution is restating the conversation_id source and the IG attachment limits, both of which the schema already covers. Baseline 3 applies.

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?

The description opens with a specific verb plus resource — "Posts a reply to an inbox conversation" — and immediately disambiguates the two resource types it covers (post comment thread vs. DM). An agent can distinguish this from list_inbox_conversations, get_conversation_messages, or like_message without opening any schema.

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?

It gives a concrete prerequisite and routes the agent to the sibling that supplies it: "Find the conversation_id with list_inbox_conversations." It also states platform-specific eligibility (7-day Meta window for IG/FB DMs, no window for comment threads and YouTube), which tells the agent when the call can succeed or fail. It stops short of naming alternatives for adjacent actions (e.g., reading a thread before replying), so it is not a full when/when-not map.

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