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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description goes much further: the URL contains an opaque per-workspace token (not the login), it is created on first request (a side effect worth flagging), it is a read-only export the calendar app cannot use to change data, and rotation is the remedy for leakage. This is exactly the behavioral context annotations cannot 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?

Four tight sentences, front-loaded with what the tool returns, then how to use it, then the security model, then the escape hatch. No filler; each clause carries distinct information.

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, yet the description states 'Returns { feed_url }', and it covers token semantics, creation timing, read-only guarantees, and rotation. Nothing an agent needs to call this correctly or explain the result to a user 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?

The tool takes zero parameters, so there is nothing to disambiguate and the baseline of 4 applies. The description correctly adds no parameter commentary and instead documents the single return field.

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 — 'Get the caller's read-only ICS calendar subscribe URL' — which is unambiguous and distinct from siblings like rotate_calendar_feed_url or get_calendar_status. An agent knows exactly what it will receive.

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 states the concrete use case ('Paste it into Google Calendar / Apple Calendar / Outlook subscribe by URL') and explicitly routes to the alternative when the condition changes ('If the URL leaks, call rotate_calendar_feed_url'). Both the when and the when-else are present.

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