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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds the important behavioral guarantee that it shares the same planner as the real scheduler, meaning the simulation is authoritative rather than approximate. It also discloses the enumerated status vocabulary the agent will need to interpret results, though it says nothing about cost or latency for large simulations.

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 what the simulation produces, then the safety guarantee, then the fidelity claim — a sensible ordering with no filler. The long parenthetical status list is dense but justified because there is no output schema to carry it.

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 fully carries the burden of explaining return contents (times, rendered copy, statuses, problems, launch_blockers) and the read-only guarantee. Nothing an agent needs in order to call this correctly against a 4-parameter schema 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 coverage is 75%; the one undocumented parameter, horizon_days, is given meaning by 'over the next N days' in the description. The remaining params (as_of, contacts, campaign_id) are already described in the schema, so the description closes the only gap.

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 (simulate) and resource (campaign send plan) and enumerates exactly what the output contains: per contact and step, send time in UTC and local, rendered subject/body, and a status enum. This is clearly distinguishable from launch_campaign or get_campaign 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?

'Nothing is written or sent' plus 'this is what the scheduler will do' makes the pre-launch dry-run use case obvious and implicitly routes the agent away from launch_campaign. However, it never explicitly names launch_campaign as the alternative or states a when-not condition, so it stops short of full routing guidance.

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