What the connected CardDAV server can do

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

Annotations already declare this as read-only, idempotent, and non-destructive. The description adds useful behavioral context beyond those hints: it performs live capability probing (checking whether optional features actually work) and warns that CardDAV implementations vary. No contradiction with annotations.

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?

Two tightly written sentences. The first front-loads the concrete output substance; the second adds a pragmatic trigger for when to call the tool. Every clause earns its place; no filler or schema repetition.

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 parameters, an output schema present, and annotations covering the safety profile, the description fully covers what an agent needs: what it reports, why it matters, and when to run it. Nothing material 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 has zero parameters, so the description is not required to explain parameter meaning. The baseline of 4 applies, and the description appropriately focuses on what the returned information will tell the agent rather than on inputs.

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 uses a specific verb ('Reports') and identifies a distinct resource: the connected CardDAV server's capabilities, including DAV compliance tokens and supported vCard versions. This clearly distinguishes it from sibling tools that operate on contacts, address books, or groups.

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 it: 'The first thing to run when something behaves differently than expected.' This gives clear contextual guidance, though it doesn't name specific alternative tools or exclusion cases, so it falls just short of a 5.

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