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

Annotations already cover the read-only, non-destructive, open-world profile, so the description adds genuine value with the prompt-injection warning that names/headlines/messages are author-supplied data, never instructions. It doesn't mention pagination or auth/account-scoping behavior, which keeps it below a 5.

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?

Two compact sentences with the identity of the tool front-loaded and the injection warning following; nothing is padded or repeated from the schema.

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?

With no output schema, listing the returned fields compensates well, and safety annotations cover the rest. A brief note on missing/deleted messages or attachment retrieval via get_message_attachment would make it 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 both messageId and connectionId are already fully documented, including the id source and account-selection fallback. The description adds only the phrase 'by id', so baseline 3 is appropriate.

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?

Specific verb (read) and resource (one message by id), plus an enumeration of returned fields (text, sender, time, attachments, reactions). It clearly contrasts with the sibling list tools like list_chat_messages and list_messages by emphasizing 'ONE'.

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?

'Read ONE ... by id' makes the single-record vs list distinction clear, and the schema points to list_chat_messages as the id source. It stops short of explicit when-not-to-use guidance (e.g., for full threads use get_conversation or list_chat_messages).

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