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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description still adds meaningful behavioral value by disclosing the exact payload fields and the 30-day cost aggregate, which matters because there is no output schema.

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?

It is a single dense sentence that front-loads the resource and then lists the returned data. It is efficient, though the long comma-delimited field list is slightly harder to scan than a short structured breakdown would be.

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 carries the burden of explaining return values and does so thoroughly. It is complete enough for an agent to call the tool correctly, with only minor omissions like pagination/ordering details that are partially covered by the schema.

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%, so both parameters (id and limit) are fully documented in the schema itself. The description adds no syntax or semantic detail beyond implying default ordering by 'newest', so the baseline 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 resource — a heartbeat monitor's newest runs — and enumerates the returned fields (outcome, duration, exit code, model, tokens, cost, 30-day cost). This clearly separates it from get_run (a single run), though it does not explicitly name that sibling or otherwise differentiate itself in prose.

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?

There is no explicit guidance on when to use this tool versus alternatives like get_run or list_monitor_events. The phrase 'newest runs' hints at recent-history use, but no conditions, exclusions, or alternative-routing advice are given.

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