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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the bar is lower; the description still adds a genuinely useful trait not in annotations — that reading does NOT mark the chat read — plus a concrete inventory of what is returned (sender_display_name, contact form details, read receipts, attachments, page_context). It omits pagination behavior despite cursor-like params.

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?

A single sentence, front-loaded with the verb and the field inventory, with zero filler. It does effectively duplicate the title verbatim and crams five payload attributes into one clause, but size is appropriate for the information conveyed.

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?

The field inventory compensates for the absent output schema, and the no-mark-as-read clause covers the main side-effect concern. However, with 7 inputs, three of them required and two having enums/cursors, leaving every parameter undocumented and giving no pagination guidance is a real gap for an agent trying to call it 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?

Schema description coverage is 0% across 7 parameters, so the description must compensate and does not: it never mentions company, environment, conversation, view, after, file_id, or receipt_after. Names like sender_display_name and page_context are response fields, not inputs, so they add no parameter meaning.

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 ("Read") and resource ("original Messenger messages") and enumerates the payload fields, so the agent knows it fetches full message content for a chat. It does not name or contrast with siblings such as summer_messenger_conversations_list or summer_messenger_email_read, so differentiation is left to the name alone.

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?

There is no explicit when-to-use guidance. The clause "without marking the chat read" hints at a distinguishing condition versus whatever tool does mark chats read, but no alternative is named and no prerequisites (company/environment/conversation required params) are mentioned.

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