Read one Messenger / Instagram DM thread

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

Annotations already provide readOnlyHint=true and destructiveHint=false, but the description goes far beyond by disclosing the reply-window computation (based on last message, not thread updated time), the Instagram truncation behavior, and the availability of replyTo. It clearly states read-only and 0 credits, aligning with readOnlyHint. No contradictions.

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?

The description is front-loaded with the core function, then explains the critical reply-window nuance, and ends with platform-specific caveats. Every sentence contributes unique value, though the length is slightly above average. It is well-structured and lacks fluff.

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 read-only tool with subtle behavior, the description covers the main gotchas: reply window semantics, Instagram truncation, and the replyTo field. Since there is no output schema, it appropriately explains return expectations. It does not mention error cases or pagination beyond limit, but that is not essential for this tool.

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 75% (3 of 4 params have descriptions). The description adds value for `platform` by explaining the Instagram 20-message ceiling, but does not clarify `pageId` or add details for `limit` beyond the schema. Given moderate coverage and modest description contribution, it meets the baseline but does not exceed it.

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 clearly states the tool reads messages in a single DM thread, oldest to newest, with inbound/outbound markers. It distinguishes itself from sibling tools like list_meta_conversations (which lists threads) and reply_to_meta_message (which sends replies) by emphasizing the reply-allowed check and the replyTo id. The verb and resource are specific and unambiguous.

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?

The description explicitly says 'Read this before drafting' — signaling when the tool should be used (prior to composing a reply). It also explains the 24-hour reply window nuance and Instagram's 20-message truncation, guiding interpretation. However, it does not explicitly name alternative tools or provide 'when not to use' conditions, so it falls short of a 5.

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