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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and a closed world, so the safety profile is covered. The description adds scope ('in the address book') and clarifies this is a pre-merge investigation that itself does not merge, but says nothing about how duplicates are matched or what the limits do.

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?

One short sentence with zero filler and no repetition of the title. It is a subordinate-clause fragment that leads with the trigger rather than the action verb, which is slightly less front-loaded than ideal but still efficient.

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 two-parameter read tool with an output schema and full annotations, the description covers trigger, scope, and pipeline position adequately. The material gap is that it does not resolve the overlap with contacts.duplicates.check, leaving tool selection ambiguous for the most likely confusion pair.

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?

Schema description coverage is 100% with only two simple parameters (contact_id required, limit defaulting to 10), so the schema carries full meaning. The description adds no syntax, format, or edge-case detail for either parameter, which is the baseline 3 case.

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 states a clear action and resource: find duplicates of a given contact, with match reasons, and situates it before merging. It is understandable on its own, but it never distinguishes itself from the very similar sibling contacts.duplicates.check, so an agent still has to guess which of the two to pick.

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 an explicit trigger ('when you suspect a contact has duplicates') and a workflow position ('before merging'), which implies the merge/unmerge siblings are the downstream step. However, it names no alternative and gives no exclusion criteria, so the check-vs-find decision is left to inference.

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