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

Annotations already declare readOnly, idempotent and non-destructive, so 'Free; changes nothing' is largely confirmatory, but the description adds real behavioral content the schema does not: newest-first ordering and the meaning of each machine.ended reason (evicted vs stopped, out_of_funds, paused, failed). It does not mention retention or result-size behavior beyond the default window.

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-loads what it is, then conditions, then cost. The middle sentence is a dense run-on with nested parentheticals, but nearly every clause carries event-type semantics that the agent needs given there is no output schema.

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?

With no output schema, the description must carry return-value meaning, and it does by explaining all three event types and their failure reasons. Pagination and the 30-day default window are left to the schema, which is acceptable; nothing an agent needs to call it is missing.

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% and both parameters (limit, since) already document their defaults and ISO 8601 format. The description adds no syntax, bounds or semantics beyond the schema, so the baseline 3 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?

Opens with a specific resource and ordering: 'Events on your machines, newest first', then enumerates the three event kinds and what each carries. It clearly differs from siblings like list_instances or get_instance, though it never names an alternative explicitly.

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?

'Check it when a machine stops answering, and after any alert on a tool result' gives concrete trigger conditions an agent can act on. It stops short of exclusions or naming the sibling (get_instance) that covers a still-running machine, so it is clear context rather than full routing guidance.

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