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draw_polyline

Draw connected line segments through a list of points to outline shapes and paths in a sprite; close the loop for polygons or enable pixel-perfect for clean pixel art.

Instructions

Draw connected line segments through a list of points.

points: list of {"x": int, "y": int}. Set closed=True to connect the last point back to the first (outline a polygon). pixel_perfect removes L-corner pixels across the whole path for a clean pixel-art outline.

Coordinates: (0, 0) is the top-left pixel. x grows right, y grows DOWN. A span given as position plus size covers x .. x + width - 1, so width is a count of pixels, not an offset to the far edge.

Centring differs between primitives, so check this when aligning two shapes:

  • draw_rectangle(x, width) spans x .. x+width-1, centred on x + (width-1)/2. An even width therefore centres on a half pixel.

  • draw_ellipse(center, radius) spans center-radius .. center+radius, which is always an ODD 2*radius+1 pixels wide and always centred on a whole pixel.

  • draw_ellipse_in_box(x, y, width, height) takes the same bounding box as draw_rectangle and fills it exactly, so it is the one to use for an even diameter, a disc centred on an even canvas, or a circle that has to line up with a rectangle.

  • draw_symmetric_pixels mirrors about the canvas, not about either of the above.

Writes falling outside the canvas are dropped rather than raising. Every drawing tool reports pixels_written, and pixels_clipped when anything was dropped, so compare those against what you asked for rather than trusting ok.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
colorYes
frameNoDefault: 1.
layerNo
closedNoDefault: false.
pointsYes
filenameYes
pixel_perfectNoDefault: false.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed14 schema fields changedv0.10.0
    • addedInput schema / properties / closed / description
      Added value: +"Default: false."
    • removedInput schema / properties / closed / title
      Removed value: -"Closed"
    • removedInput schema / properties / color / title
      Removed value: -"Color"
    • removedInput schema / properties / filename / title
      Removed value: -"Filename"
    • addedInput schema / properties / frame / description
      Added value: +"Default: 1."
    • removedInput schema / properties / frame / title
      Removed value: -"Frame"
    • removedInput schema / properties / layer / anyOf
      Removed value: -[
      -  {
      -    "type": "string"
      -  },
      -  {
      -    "type": "null"
      -  }
      -]
    • removedInput schema / properties / layer / default
      Removed value: -null
    • removedInput schema / properties / layer / title
      Removed value: -"Layer"
    • addedInput schema / properties / layer / type
      Added value: +"string"
    • addedInput schema / properties / pixel_perfect / description
      Added value: +"Default: false."
    • removedInput schema / properties / pixel_perfect / title
      Removed value: -"Pixel Perfect"
    • removedInput schema / properties / points / title
      Removed value: -"Points"
    • removedInput schema / title
      Removed value: -"draw_polylineArguments"
  2. First observedv0.7.0

TDQS

A4.3/5.0
Behavior5/5

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

Annotations only declare readOnlyHint=false and openWorldHint=false, so the description carries the behavioral burden and does so well: out-of-canvas writes are silently dropped rather than raising, and every drawing tool reports pixels_written/pixels_clipped, with the explicit warning to compare those rather than trusting 'ok'. That is exactly the failure-mode context an agent needs before a write.

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?

Purpose is front-loaded, followed by parameter semantics, then coordinate conventions and clipping behavior; each block earns its place. The multi-bullet centring comparison is tangential to this specific tool and could be relegated elsewhere, which keeps it from a full 5.

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

Completeness4/5

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

With no output schema, the description steps in to describe the returned pixels_written/pixels_clipped counters and the clipping failure mode, plus the coordinate system and centring conventions. The only remaining gap is the semantics of color, frame and layer, which an agent must infer.

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 coverage is only 43%, so the description must compensate, and it does for the non-obvious parameters: points is defined as a list of {x:int, y:int}, closed is explained as connecting last point to first, and pixel_perfect removes L-corner pixels. color, frame, layer and filename remain undocumented in both schema and description, which keeps it short of a 5.

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?

The opening sentence names a specific verb and resource — 'Draw connected line segments through a list of points' — which is clearly distinct from siblings like draw_line, draw_curve, draw_rectangle and draw_ellipse. An agent can identify the tool's job without inspecting the schema.

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

Usage Guidelines3/5

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

It hints that closed=True produces a polygon outline, but it never states when to prefer draw_polyline over draw_line or draw_curve. The comparative guidance it does give (draw_ellipse_in_box vs draw_rectangle centring) is about other primitives rather than about selecting this tool.

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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