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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description earns credit for behavior annotations cannot express: the result doubles as the snapshot baseline for the /api/realtime/ subscription, after which updates arrive as events. It omits any statement about ordering, volume, or pagination for large site lists.

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 sentences, front-loaded with the returned state before the realtime relationship. The trailing clause about screens never polling is slightly promotional but still carries the practical implication of the snapshot semantics.

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 single-parameter, read-only list tool with full annotation coverage and no output schema, the description covers what is returned (states plus last check) and how it fits the realtime flow. Only scale/ordering details are absent, a minor gap at this complexity.

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 100% and the single guest_token parameter is documented in the schema itself (X-Guest-Token header, owner scoping, reuse). The description adds no parameter meaning beyond that, so the baseline of 3 for a well-covered schema applies.

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 names the resource ('every site you monitor') and specifies exactly what is returned ('the state ... up, down, waiting, paused, with the last check'), which is more precise than the name alone. It stops short of an explicit verb and does not distinguish itself from look-alike siblings such as check_site or list_events.

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?

Usage is implied rather than stated: the realtime note ('after it, every check arrives as an event, so a screen never has to poll') suggests taking this snapshot first and then consuming events. There is no explicit when-to-use or when-not-to-use guidance versus check_site or list_events, so the agent must infer the choice.

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