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Read pixels

read_pixels

Read-only

Read a rectangular region of pixels as structured data, returning distinct colors and an index grid, for computational tasks like sampling palettes or detecting edges.

Instructions

Read a rectangular region as structured data: a list of distinct colours plus a row-major index grid. Use this when you need to compute over pixels (sample a palette from art, find a silhouette edge, copy a region) rather than just look at them. For eyeballing, 'look' is cheaper.

Input Schema

TableJSON Schema

Name	Required	Description
`frame`	No	1-based frame number. Omit to use the active frame.
`layer`	No	Layer name. Omit to use the active layer.
`region`	No	Omit to read the whole canvas.
`sprite`	No	Which sprite: its id as '#7' (what every result reports back, and the only unambiguous form — two unsaved documents are both called 'Sprite'), its filename, or its display name. Omit to use the sprite Aseprite has focused.
`composite`	No	Read the flattened image. False reads only the target layer's cel.

Output Schema

TableJSON Schema

Name	Required	Description
`x`	Yes
`y`	Yes
`grid`	Yes	Row-major indices into `colors`.
`width`	Yes
`colors`	Yes	Distinct colours; index 0 is fully transparent.
`height`	Yes
`sprite`	Yes
`uniqueColors`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedv0.1.6Sep 9, 2026

changedInput schema / properties / sprite / description

Previous value: -"Sprite filename or id. Omit to use the sprite Aseprite has focused."New value: +"Which sprite: its id as '#7' (what every result reports back, and the only unambiguous form — two unsaved documents are both called 'Sprite'), its filename, or its display name. Omit to use the sprite Aseprite has focused."

First observedv0.1.0Sep 8, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true, so the read-only behavior is known. The description adds value by describing the output structure ('a list of distinct colours plus a row-major index grid'), which goes beyond the annotation. It doesn't contradict annotations and provides useful context about the tool's non-mutating nature and return format.

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

Conciseness5/5

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

The description is concise: two sentences that front-load the core function, then provide usage context and an alternative. Every word earns its place, with no redundancy or fluff.

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 the tool has an output schema (as indicated by context signals), the description does not need to detail return values. It covers purpose, usage, and differentiation from a key sibling. With read-only annotations and a fully documented parameter schema, the description is complete for an agent to select and invoke correctly.

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

Parameters3/5

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

The input schema has 100% coverage with descriptions for all 5 parameters, including nested 'region' details. The tool description does not add any additional parameter-specific meaning beyond what the schema already provides. Per calibration, with high schema coverage, baseline is 3, and no extra param info is given, so this is appropriate.

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 description clearly states the tool's function: 'Read a rectangular region as structured data: a list of distinct colours plus a row-major index grid.' It uses a specific verb (read) and resource (rectangular region), and explicitly differentiates from the sibling 'look' tool by contrasting computation vs. eyeballing. This allows an agent to distinguish it immediately.

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 explicit usage guidance: 'Use this when you need to compute over pixels (sample a palette from art, find a silhouette edge, copy a region) rather than just look at them. For eyeballing, 'look' is cheaper.' This clearly states when to use this tool and when to use an alternative, leaving no ambiguity.

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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