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zoom_region

Magnify a region of the current screenshot at native resolution to read exact coordinates on canvases or custom views before clicking. The zoomed area becomes the new click coordinate space.

Instructions

Zoom into a rectangle of the CURRENT image (the last screenshot's pixel space) and re-capture it at native resolution — a sharp, legible magnified view. Only that rectangle is captured (not the whole display), so it is also smaller and quicker to take than a full-display shot. Use it to read exact positions on surfaces that expose no marks (canvas/games, custom-rendered views) before clicking, or to stay scoped while working inside one area. Pass x, y, width, height in the current image's pixels (width,height > 0). The returned image becomes the new coordinate space, and clicks afterward map into the zoomed region automatically. marks defaults OFF (read coordinates off the overlaid grid); grid defaults ON. Take a screenshot first so there is an image to zoom into.

Input Schema

NameRequiredDescriptionDefault
xYesLeft edge of the rectangle, in the CURRENT image's pixel space (the last screenshot's coordinates).
yYesTop edge of the rectangle, in the current image's pixel space.
gridNoOverlay a labeled coordinate grid. Defaults ON for a zoom (coordinate mode); pass grid=false to suppress it.
marksNoSet-of-Mark numbering. Defaults OFF for a zoom — the zoom is the tool for surfaces that expose no marks, so you read coordinates off the grid. Pass marks=true to also number any actionable elements inside the region.
widthYesWidth of the rectangle in current-image pixels. Must be > 0.
heightYesHeight of the rectangle in current-image pixels. Must be > 0.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.3.0
    • removedInput schema / title
      Removed value: -"ZoomRegionParams"
  2. First observedv0.1.0

TDQS

A4.8/5.0
Behavior5/5

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

No annotations exist, so the description carries the full burden and does so richly: only the rectangle is captured (not the whole display), it is smaller/quicker, the returned image becomes the new coordinate space, and subsequent clicks automatically map into the zoomed region. It also discloses the non-obvious defaults (marks off, grid on) and the reason behind them.

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?

The core action and scope constraint are front-loaded, and nearly every sentence earns its place (caveats, defaults, coordinate-space behavior, prerequisite). Minor padding such as 'a sharp, legible magnified view' keeps it from a 5.

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?

With no output schema and no annotations, the description still explains what the returned image means (new coordinate space, automatic click remapping) and the prerequisite screenshot. Nothing an agent needs to call this correctly is missing.

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

Parameters4/5

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

Schema description coverage is 100%, so baseline is 3; the description adds value by framing x/y/width/height as current-image pixel space with width,height > 0 and by explaining the intent behind the grid/marks defaults. It does not add new syntax or ranges beyond the schema, so it stays just above baseline.

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?

States a specific verb+resource+scope: zoom into a rectangle of the CURRENT image and re-capture at native resolution, distinguishing it from a full-display screenshot in the same sentence. An agent can tell this apart from sibling 'screenshot' without opening either schema.

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?

Explicit when-to-use: read exact positions on surfaces that expose no marks (canvas/games, custom-rendered views) before clicking, or to stay scoped within one area. It also names the prerequisite (take a screenshot first) and the trade-off versus a full-display capture.

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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