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

With readOnlyHint and idempotentHint annotations covering safety, the description adds valuable context that the operation lists all contacts in the caller's own address book, implying a comprehensive read. It does not contradict annotations and provides enough behavioral clarity for a simple list operation.

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 a single, concise sentence with no wasted words. It is front-loaded with the verb and clearly states the scope and resource.

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 simple, parameterless list tool, the description is complete. With no output schema required and annotations covering safety, it fully explains what the tool does. The sentence provides all necessary context for an agent to select and invoke the tool correctly.

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?

There are no parameters, and schema coverage is 100% (vacuously). The baseline for zero parameters is 4, and the description adds no parameter information because none exists. This 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 'List everyone in the caller's address book' uses a specific verb ('List') and resource ('address book'), and clearly differentiates from sibling tools like contacts_add, contacts_delete, and contacts_find by indicating a full listing rather than a targeted search or mutation.

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?

The description gives clear context for use (browsing all contacts in the caller's address book), but does not explicitly mention alternatives or when not to use it. The lack of parameters and mention of 'everyone' imply a broad listing, but no direct comparison to contacts_find is provided.

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