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

Annotations already flag destructive=true, idempotentHint=false and openWorldHint=true; the description adds genuinely new behavioral context beyond them — that user approval must be preserved and that an uncertain failure must be resolved by state inspection rather than retry. It does not say whether the acceptance can be undone or what changes post-acceptance, which keeps it at 4.

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 short sentences with the core action front-loaded and total absence of filler. The 'External action:' label is slightly jargon-y but still efficiently signals the consent requirement.

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 destructive, non-idempotent mutation with no output schema and fully documented parameters, the description covers the two things an agent most needs: consent gating and non-retry semantics. Missing only post-state information (what happens to the thread after acceptance, whether it is reversible).

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% and the per-parameter text is already detailed (exact chat.id format, PAGE_<page_id>_INBOX, account_id disambiguation rules). The description adds no parameter-level meaning of its own, so the 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?

States a specific verb (accept) and resource (a message request) plus the scope constraint (in its original inbox), which separates it from facebook_accept_friend_request and from listing tools like facebook_list_inbox_chats. It never explicitly names a sibling to contrast with, so it stops short of a 5.

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?

'External action: preserve explicit user approval' establishes the precondition for calling it, and 'never retry after an uncertain failure; inspect current state first' gives clear failure-path guidance. It does not tell the agent where to obtain inbox_id/chat_id (e.g., facebook_list_inboxes), so routing to prerequisites is left implicit.

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