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

Beyond the annotations, the description discloses important behavior: listing does not advance the unread cursor, has_more controls whether to call again, and sequence gaps correspond to non-message events rather than missing data. It also repeats idempotency and gives the REST endpoint, which helps an agent reason about side effects and retries.

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 tool's core purpose, followed by cursor behavior, pagination, sequence-gap caveats, and sibling preference. Each sentence supplies actionable information, and there is no filler.

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?

Although there is no output schema, the description names the returned fields (id, seq, body, kind), explains pagination and cursor behavior, and accounts for sequence gaps. That is complete enough for an agent to call and continue 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?

The schema already documents the since parameter fully, so the baseline is 3. The description adds operational meaning by explaining that has_more should trigger another call with since set to the last seq and by clarifying that sequence gaps may come from other event types.

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 verb and resource: list Space messages after an optional sequence. It also names the sibling alternative, receive_unread_messages, and explains when this tool is preferred, so an agent can distinguish it without opening the 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?

It explicitly says to prefer this tool over receive_unread_messages when the goal is browsing, and it explains pagination via has_more and since. The main when-to-use distinction is stated directly rather than left to inference.

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