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

With no annotations, the description carries the full burden and does disclose the key side effect that sending a message lets the candidate reply in messenger. However, it does not mention other behavioral factors such as permissions, external send effects, or the requirement to provide subject and recruiterContact when opening a new thread, leaving some transparency gaps.

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 two short sentences with the mode behavior front-loaded and an English summary for accessibility. Every word contributes to understanding the tool without redundant filler.

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 tool with three modes and no annotations, the description covers the core dispatch rules and the async reply behavior. It relies on the rich 100%-covered schema for parameter requirements like subject/recruiterContact, and it does not describe return values since there is no output schema; these are minor gaps rather than blockers.

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 covers all five parameters with descriptions, so the baseline is 3. The description adds value by specifying the parameter-combination logic (absence of text/conversationId = list, conversationId = history, text = send), which is not fully captured by any single schema field.

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 clearly identifies the tool's purpose as messaging with a candidate and enumerates three specific actions: listing threads, reading a thread history, and sending a message. This disambiguates it from sibling tools like send_vacancy or ask_about_experience because it owns the candidate-correspondence domain.

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 explicit mode-selection rules based on parameter presence: no text/conversationId lists threads, conversationId reads history, text sends a message. This is clear context, though it does not explicitly name sibling tools or state when not to use this tool in favor of an alternative.

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