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

The annotations already show this is a non-read-only, non-idempotent action, but the description adds meaningful behavioral caveats: alarms are inexact to preserve battery, delivery is best-effort, and a phone that never receives the setup message never arms the reminder. It also discloses the reminder_id return value, which is the natural hook for cancel_reminder. This goes well beyond what annotations or schema reveal.

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?

The description is compact and front-loaded: purpose, use case, parameter constraint, delivery caveat, and return value appear in a sensible order with no filler. Every sentence contributes a distinct piece of information an agent needs before calling the tool.

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 two parameters, an output schema, and clear sibling relationships, the description covers all important operational risks: timing units, server-enforced bounds, local firing semantics, best-effort delivery, and the returned reminder_id. There is nothing material an agent would need to know about correct invocation that 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 100%, so the schema already documents both parameters. The description reinforces the critical facts that 'at' is an absolute Unix timestamp in SECONDS and must be within 60 seconds to 365 days, but it does not introduce meaning beyond what the schema already states. Baseline 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 opens with a specific verb and resource: 'Schedule a notification to appear on the user's phone at a specific future time.' This clearly distinguishes it from immediate-send siblings like send_notification and pairs naturally with cancel_reminder. An agent can confidently identify what this tool does without needing to inspect the 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?

It gives an explicit when-to-use trigger: 'Use this when the user asks to be reminded of something later.' It does not explicitly state when-not-to-use or name an alternative like send_notification for immediate delivery, so it stops one step short of full routing guidance. Still, the context is clear enough for correct selection in most cases.

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