left_mouse_down

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

With no annotations, the description carries the burden. It discloses the hold action, error if already held, and the allowlist requirement. It does not discuss edge cases like dragging, but the core behavior is well covered.

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 three sentences, front-loaded with the action, and every sentence adds value. No redundancy or unnecessary information.

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 param-less tool with no output schema, the description covers purpose, prerequisites, sequence, and error conditions. It is complete and leaves no ambiguity about how to use the tool.

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 no parameters, so the schema describes them all. The description adds context about usage that goes beyond the schema, making it helpful for an agent. Given zero parameters, a baseline of 4 is appropriate.

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 states the action: press and hold the left mouse button. It distinguishes itself from siblings like left_mouse_up and left_click by explaining the hold behavior and the release step.

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?

Provides step-by-step context: use mouse_move first, call left_mouse_up to release. Also specifies the prerequisite that the frontmost app must be in the allowlist. No explicit when-not-to-use, but the guidance is clear.

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