left_mouse_down

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

No annotations are provided, so the description carries the full burden. It clearly discloses the hold behavior and that release requires left_mouse_up, which is key. The persistent session requirement is also stated. Could mention potential issues if already pressed, but overall adequate.

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?

A single sentence that efficiently conveys the action and the prerequisite. No unnecessary words or details. Perfectly front-loaded.

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 one-parameter tool with no output schema, the description covers the essential behavior, coordinate meaning, and session requirement. It also references the companion tool for release. Minor omission: no mention of constraints like coordinate bounds or timeout.

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 already provides a complete description of the coordinate parameter (format, constraints, meaning). The description adds no further semantic value beyond what the schema states, so baseline 3 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 explicitly states 'Press and hold the left mouse button' with a clear verb and resource. It distinguishes from sibling tools like left_click (press and release) and left_click_drag (press, move, release) by noting the hold action and release via left_mouse_up.

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 implies usage when a persistent mouse press is needed, but no explicit when-to-use or when-not-to-use guidance is given. It mentions the persistent session requirement but does not contrast with alternatives like left_click or left_click_drag.

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