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

Beyond annotations (readOnly=false, idempotent=false, destructive=false), the description discloses visible side effects: the item appears on the phone as a Planned run, the person can move or delete it there, it begins at that moment, and the answer carries `run`. It stops short of stating whether re-planning the same moment duplicates a plan (relevant given idempotentHint=false) or what happens on conflict.

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 plus a comma-clause, front-loaded with the core action and the future-moment scope. Every clause adds usable information — example, phone visibility, timezone requirement, return field — with 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?

There is no output schema, but the description names the return payload (`run`). With 5 parameters at full schema coverage, the description covers the remaining questions an agent would have: deferred timing, phone-side editability, timezone format, and start_run-consistent naming/values.

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 baseline is 3, and the description earns a bump by adding a real constraint not spelled out in prose in the schema: the moment must carry its time-zone offset in ISO 8601. It also tells the agent `name`/`values` behave as in start_run, which is useful cross-tool semantics beyond the per-field schema text.

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 specific verb and resource ('Plans a run of one of the person's routines') and pins the distinguishing scope: a future moment rather than now. The example 'Morning tomorrow at seven' and the contrast with start_run ('Takes name and values as start_run does') let an agent tell it apart from the sibling without opening either 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?

The description makes clear when to use it: scheduling for a moment to come, as opposed to start_run for immediate execution. It explicitly covers the ask_first case via the schema, but does not state an explicit exclusion ('do not use to run now') or what happens if the moment is invalid/in the past.

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