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Capture the main display or a window as a base64 JPEG with pixel dimensions. Read target coordinates from the image to execute precise mouse clicks — subsequent actions map to this coordinate space.

Instructions

Capture the screen — the whole main display, or a single window with window="" — and return a base64 JPEG plus a text note with its pixel dimensions. ALL coordinate-taking tools (mouse_move, *_click, scroll) expect coordinates in THIS image's pixel space — origin (0,0) top-left, x right, y down — so read target positions directly off the returned image; subsequent clicks are mapped through it automatically. PREFER window="" (substring of its title or app name) over the whole display whenever you are working inside one app: a full-display shot is downscaled to ~1280px wide, so small UI (list rows, sidebar items, buttons) becomes only a few pixels — too small to read or click accurately. A window capture is larger and sharper, returns a smaller image (fewer pixels → less context, faster turn), and clicks map into the window automatically. marks is ON by default: it boxes+numbers actionable elements (needs Accessibility) and lists each as [N] — activate one with click_mark(number=N), the most reliable way to click with no coordinate guessing. A magenta coordinate grid (for reading x/y) is shown automatically when marks is off and hidden when it is on; pass grid=true to force both, or marks=false for pure coordinate mode. If a target is still too small to click, use zoom_region to magnify part of this image.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
gridNoOverlay a labeled coordinate grid (magenta rules + pixel labels) for reading off click coordinates. Omitted by default it follows the AX-first rule: OFF when `marks` is on (you click by number, not coordinates), ON when `marks` is off (coordinate mode). Pass grid=true to force it on alongside marks, or grid=false to suppress it.
marksNoSet-of-Mark: number every actionable UI element (buttons, links, fields) and list each as `[N] role "label"`, so you can activate it with click_mark(number=N) — the most reliable targeting, no coordinate guessing. Defaults ON (AX-first). Needs Accessibility permission. Covers native controls AND web content — real links/buttons on semantic pages, and on div-rendered pages (e.g. webmail) the list rows are numbered too (their click lands via a coordinate at the row center). Only canvas/game- style surfaces with no AX come back empty. Pass marks=false for pure coordinate mode.
windowNoCapture only a single on-screen window instead of the whole display — a case-insensitive substring of the window title or app name (e.g. "Safari", "Settings"). Smaller, sharper image = less context and better click precision. Subsequent clicks map to this window automatically.
Behavior5/5

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

With no annotations, description fully discloses behaviors: downscaling of full display, coordinate system, default marks-on behavior, grid display logic, and limitations for canvas surfaces.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Well-structured with clear sections, but somewhat lengthy. Could be trimmed slightly without loss of essential information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given complexity (3 optional params, no output schema), description completely covers return format, coordinate mapping, defaults, and fallback suggestions.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema has 100% parameter descriptions, but description adds valuable context: default interaction between grid and marks, substring matching for window, and preference for window capture.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description explicitly states it captures screen or window and returns base64 JPEG with dimensions. It also explains how coordinates relate to the image, clearly distinguishing it from sibling tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides clear when-to-use guidance: prefer window capture when working inside an app, when to use marks vs grid, and when to fall back to zoom_region for small targets.

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

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