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

Annotations are thin (readOnly=false, destructive=false), so the description carries the behavioral burden — and it delivers: the alarm is inexact to preserve battery, delivery is best-effort, and a phone that never receives the setup message never arms the reminder. These failure-mode and timing disclosures go far beyond anything the annotations express.

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?

Purpose is front-loaded in the first sentence, and each subsequent sentence earns its place: when to use, parameter units/range, timing inexactness, delivery failure mode, and return-value routing. At roughly 110 words it is not minimal, but the density of operational caveats justifies the length.

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 2-param tool with an output schema, nothing material is missing. The description covers trigger phrase, parameter constraints, timing guarantees, the delivery failure mode, and how the return value is consumed. An agent can invoke this tool correctly and set expectations appropriately without any further research.

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?

Even with 100% schema coverage, the description adds the crucial semantic that `at` is an absolute Unix timestamp in SECONDS within 60 seconds to 365 days from now. The 'from now' relative constraint and seconds-units clarification prevent real invocation bugs that the schema's bare integer bounds cannot convey.

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?

Opens with a specific verb+resource: 'Schedule a notification to appear on the user's phone at a specific future time.' This cleanly separates it from siblings like send_notification (immediate delivery) and cancel_reminder (cancellation), and the closing sentence explicitly ties the return value to cancel_reminder.

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?

Explicitly states when to use: 'Use this when the user asks to be reminded of something later.' It also names the complementary sibling (cancel_reminder). However, it never explicitly says when NOT to use it versus send_notification, though the scheduled-vs-immediate distinction is strongly implied.

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