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Selection

select

Idempotent

Read or change the active selection to scope drawing, transforms, and recoloring. Supports rectangle, ellipse, color match, invert, grow, shrink, and combine modes.

Instructions

Read or change the active selection. Ops: 'get', 'none', 'all', 'rect', 'ellipse', 'color' (select every pixel matching a colour), 'invert', 'grow', 'shrink'. A selection scopes draw, transform and recolor, which is usually cheaper and safer than masking by hand.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`op`	Yes
`mode`	No	How this selection combines with the existing one.	replace
`rect`	No
`color`	No	For op 'color'.
`frame`	No	1-based frame number. Omit to use the active frame.
`layer`	No	Layer name. Omit to use the active layer.
`amount`	No	Pixels, for grow/shrink.
`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.
`tolerance`	No
`contiguous`	No	For op 'color'.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`empty`	Yes
`bounds`	No
`sprite`	Yes
`pixelCount`	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

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=false and idempotentHint=true. The description adds that the tool reads or changes the selection and that it affects downstream operations, which is useful behavioral context beyond the annotations. No contradiction found.

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?

Two sentences, front-loaded with the main action and a concise op list. The note about scoping is valuable and adds no fluff.

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?

Given 10 parameters, a nested object, and an output schema, the description covers the tool's purpose and effect on other operations. It does not explain return values (output schema exists) or detailed param behaviors (schema covers most). Adequate for agent use.

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 schema provides descriptions for several parameters (mode, color, frame, layer, amount, contiguous, sprite). The description itself only clarifies the 'color' op. With 70% schema coverage, the description adds marginal value over the schema, so baseline 3 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 states the verb 'read or change' and the resource 'active selection', then enumerates the supported operations. It clearly distinguishes this tool from drawing/transform/recolor operations by explaining that selection scopes them, which separates 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 Guidelines4/5

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

The description explains that a selection scopes draw, transform and recolor, and notes it is cheaper/safer than manual masking. This gives clear context for when to use selection, though it does not explicitly name alternatives or list exclusions.

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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