List Address Books

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds one genuine behavioral fact beyond that – it returns empty books that searchContacts hides – but says nothing about ordering or scale of the result set.

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?

Compact, note-style, and front-loads the field list with the createContact linkage flagged inline. The opening fragment "Address books MCP clients may use:" is slightly awkward, but nothing is padding.

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 output schema, return-shape disclosure is the description's main job; it names addressBookId, name, readOnly and default but omits value types and any indication of how many books come back. Adequate for a simple list tool, but not fully self-contained.

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 zero input parameters, so the baseline is 4; however, the description's field list is really describing returns, not inputs, and it doesn't explain formats (e.g. what readOnly/default values look like). It adds useful meaning but not fully at the level expected for a no-param tool.

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 names the resource (address books) and the action ("Lists"), and enumerates the fields returned, so an agent knows exactly what it gets back. It implicitly separates itself from searchContacts by noting it lists empty books that searchContacts cannot show, though the verb appears only in the second sentence.

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 concrete usage context: addressBookId is what createContact needs, and the "default" book is used when createContact receives no addressBookId. It also carves out a niche versus the sibling searchContacts (empty books). It stops short of an explicit "call this before createContact" instruction, but the routing is clear.

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