Read LINE messages

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

Annotations already provide readOnlyHint, openWorldHint, and idempotentHint, covering safety and idempotency. The description adds valuable context beyond that: 'Side-effect free: no files written' reinforces read-only, and 'Only rows rendered on screen are visible (virtualized list)' discloses a critical limitation about what data is accessible. This enriches the agent's understanding of the tool's behavior.

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 two concise sentences. The first sentence front-loads the primary action and the optional room behavior, while the second adds critical behavioral caveats. No unnecessary words or redundancy; every sentence earns its place.

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 tool has 9 parameters but none required, and an output schema exists to define return values. Annotations cover read-only, idempotent, and open-world aspects. The description explains the core operation and the virtualization limitation, which is the key behavioral constraint. Combined with schema and annotations, the agent has enough information to call the 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 89%, so most parameters are already documented in the input schema. The description does not add additional meaning to parameters beyond what the schema provides; it only mentions `room` in passing. Since the schema carries the heavy lifting, a baseline score of 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?

The description states a specific action: 'Read latest messages, opening a room first when `room` is given.' This clearly identifies the verb (read) and resource (LINE messages), and the optional room-opening behavior. It distinguishes from siblings like search_messages (search) and unread_digest/unread_full (unread summaries) without needing to name them.

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 implies usage for reading messages from the current view or a specified room, but it does not explicitly contrast with sibling tools or state when to prefer this over search_messages or unread_* tools. The context of sibling names suggests differentiation, but the description itself provides no explicit when-to-use guidance or exclusions.

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