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

readOnlyHint=true already declares the safety profile, so the bar is lower. The description adds genuine behavioral context the annotation does not: the return payload shape, the meaning of `has_more`, and that older messages remain pageable. It does not mention auth or per-account constraints beyond what on_behalf_of's schema already says.

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?

Front-loaded summary sentence with the routing instruction second, then a compact returns block. No filler, and the structured tags make the output contract scannable.

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?

There is no output schema, so the description carries the full return-value burden and does so with the returns block (title, count, has_more, message fields). Combined with schema-documented pagination, an agent has everything needed to call and consume this tool 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 100%, so limit, offset, session_id and on_behalf_of are already fully documented, including the paging semantics of offset. The description adds no parameter-level detail beyond the schema, which is the expected baseline when the schema does the heavy lifting.

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 and resource ("Retrieve readable messages from a past chat session") and implicitly distinguishes itself from search_chat_history by positioning itself as the read step after discovery. An agent can tell which of the two chat tools to call without opening either 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?

Explicitly instructs to call search_chat_history first to obtain the session_id, which is a real precondition and routes the agent correctly. It stops short of stating when *not* to use this tool (e.g., live/active sessions or non-chat message sources), so it is clear context without full exclusions.

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