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

Annotations already flag destructiveHint=true and readOnlyHint=false, so the agent knows this mutates state. The description adds only that validation is reused; it does not say whether the prior schedule is overwritten, whether the send must be pending, what validation failures look like, or whether the operation is reversible — meaningful gaps for a destructive mutation.

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?

A single short sentence with the action front-loaded and no wasted words. Its brevity is efficient, though it borders on under-specification rather than tightness.

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 destructive, no-output-schema mutation with a nested required object and 0% parameter documentation, the description leaves out the essentials: what must be true beforehand, what the scheduled_at value means, and what changes occur. It is too thin for the tool's complexity and sibling density.

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 0% with two required parameters, including a nested body requiring scheduled_at. The description mentions nothing about scheduler_id or the format/timezone expectations of scheduled_at, so it does not compensate for the undocumented schema.

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 ('Reschedule') and resource ('an upcoming send'), which is clearly distinguishable from cancel_upcoming_send and edit_upcoming_send by implication. It does not explicitly name or contrast with those siblings, so it stops short of a 5.

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 guidance on when to use this versus edit_upcoming_send or cancel_upcoming_send, nor any prerequisites such as needing the send to still be pending. The only hint is 'existing scheduling validation', which does not tell an agent how to choose between siblings.

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