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

Annotations already signal read-only and non-destructive behavior. The description adds meaningful behavioral context: it requires Zalo to be connected and, if not, returns an actionable connect hint instead of an empty list. This goes beyond the annotations without contradicting them.

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 sentences with no filler. The primary purpose is front-loaded, and the prerequisite/failure behavior is added compactly in the second sentence.

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, zero-required-parameter read-only list tool, the description covers purpose, scope, prerequisite, and the key error behavior. A minor gap is that the return shape is not described and the relationship between 'limit' (described as 'friends') and 'chats' (friends and groups) is slightly ambiguous, but overall it is sufficient.

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 schema already documents the only parameter 'limit' with 100% coverage, so the baseline is 3. The description does not add parameter-level meaning beyond what the schema provides, but it does not need to in this 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 uses a specific verb and resource ('Lists your Zalo conversations') and adds concrete scope ('friends and groups') plus an intended use ('pick a recipient'). This clearly distinguishes it from sibling tools like zalo_read_messages, zalo_search_messages, or similar list tools for other platforms.

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 clear context for when to use the tool—before picking a recipient for a message—and states the prerequisite that Zalo must be linked. It does not explicitly name alternatives or say when not to use it, so it stops 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.