weixin_contacts

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

With no annotations provided, the description carries the full burden. It clearly indicates this is a read/list operation and discloses the return fields: userId, lastSeen, lastText, contextToken, msgCount. It lacks details like pagination or ordering, but for a simple list tool, it is sufficiently transparent.

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 concise sentences: first states the purpose, second lists return fields and provides a practical usage hint. No redundant words, front-loaded with the key action.

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 zero-parameter tool with no output schema, the description covers the essential return values and the next step (using userId in weixin_send). It could mention ordering or that lastSeen is a timestamp, but the information provided is sufficient for most use cases.

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 input schema has zero parameters, so the baseline is 4. The description adds meaning beyond the schema by explaining the output fields and how to use the resulting userId, which is valuable context.

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 opens with a specific verb and resource: 'List users who have messaged the bot.' It clearly states the tool's function and differentiates from sibling tools like weixin_send and weixin_poll, which involve sending or polling messages rather than listing contacts.

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 provides clear context: use this tool to discover users who have messaged the bot, and then use the returned userId as the 'to' parameter in weixin_send. It doesn't explicitly name alternatives or exclusions, but the downstream usage is implied and sufficient for a contact-listing tool.

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