left_click

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

With no annotations, the description carries the full burden and it does disclose a real behavioral trait: the allowlist gate and the failure mode (returns an error and performs no action). It does not cover timing, focus side effects, or what modifiers do, but the key safety-relevant behavior is stated.

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 short sentences with zero waste; the action is front-loaded and the constraint follows. Nothing is repeated and nothing needs expanding.

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 two-parameter mouse action with no annotations and no output schema, the description covers the essential gating behavior. The only shortfall is that the meaning and consequences of the optional modifier parameter are left entirely to the schema.

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?

Schema description coverage is 100%, so both parameters are already documented in the schema with detailed semantics (pixel coordinates read from the screenshot, modifier key syntax). The description adds nothing about parameters beyond 'given coordinates', so the baseline 3 applies.

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?

States a specific verb (left-click) and a specific resource (the given coordinates). The word 'left' inherently disambiguates from the sibling tools right_click, middle_click, double_click and triple_click, so an agent can pick it without opening others' schemas.

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 a concrete precondition for use: the frontmost application must be in the session allowlist, otherwise the call errors and does nothing. It does not explicitly say when to prefer this over left_mouse_down/left_mouse_up or double_click, so it stops short of full routing guidance.

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