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

Adds substantial behavior beyond the annotations: it clarifies what is NOT affected (customer agent clock, wall-clock leases, no rewind, no target execution) and warns that 'complete receipt means action recorded, not destination reached', directing the agent to inspect result.reachedUs and failures. This receipt-vs-effect distinction and the reconcile-with-exact-key guidance are exactly the kind of operational context annotations can't convey.

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-loaded with the core action and every sentence carries operational weight (permissions, exclusions, receipt caveat, idempotency). Dense but not padded; the only cost is high information density in one block, which slightly reduces scannability.

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 10-param destructive mutation with no output schema, the description covers preconditions, side-effect boundaries, the result fields to check (reachedUs, failures), and uncertainty handling via operationKey. An agent has everything needed to invoke and reconcile 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 coverage is only 10% (only operationKey documented), so the description carries most of the burden and does well: toUs is clarified as an absolute clock target, maxEvents as the event processing cap, and the prerequisite inputs (virtualTimeUs, instance, epoch) are tied to where to read them. It still leaves some parameters (reason, service, projectId, environmentId) unelaborated, so not a full 5.

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?

States a precise verb+resource+scope: 'Advance one active run's managed Tool clock to absolute toUs, processing at most maxEvents (1–1000) scheduled events.' No sibling tool touches the managed clock, so the agent can distinguish it immediately, and the scope (one active run, absolute target, bounded events) is explicit.

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?

Gives concrete preconditions ('Read run_services for explicit clockAdvance permission, current virtualTimeUs, instance and epoch first. Requires service-control.2 clock.advance in the retained recipe') and explicit exclusions ('Does not advance the customer agent clock, extend wall-clock leases, rewind, or execute a target'), including the non-obvious rule that invoke authority never implies clock permission.

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