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MalloyTheDev

Aseprite MCP

by MalloyTheDev
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

modify_selection

Expand, contract, or outline the current selection by a pixel amount to isolate edges for outlines or contact shadows in Aseprite sprites.

Instructions

Grow, shrink, or outline the current selection.

Args:
    op: "expand" grows by `quantity` pixels, "contract" shrinks, "border" replaces
        the selection with a band of that width around its edge. A border selection
        is how you scope an outline or a contact shadow to where two forms meet.
    quantity: How many pixels, at least 1.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
opYes
filenameYes
quantityNoDefault: 1.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv0.10.0

TDQS

B3.3/5.0
Behavior2/5

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

Annotations provide only readOnlyHint=false and openWorldHint=false. The description does not state what happens to the prior selection, whether the operation is destructive/irreversible, error conditions (e.g., no active selection), or permission requirements. For a mutating tool, this leaves substantial behavioral gaps.

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?

Front-loaded purpose sentence followed by per-parameter explanation; efficient and organized. The 'Args:' block formatting is slightly verbose but every line carries information.

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

Completeness3/5

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

With no output schema and thin annotations, the description covers op and quantity adequately but omits filename entirely and says nothing about mutation semantics or post-conditions. It's adequate to invoke the tool but not complete for a mutation on shared state.

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 only 33% (only quantity has a description), so the description must compensate. It does add real meaning: explains that op takes one of three named values and what each does, and that quantity is in pixels with a minimum of 1. It does not document the filename parameter at all, leaving one gap.

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

Purpose4/5

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

States a specific verb (grow, shrink, outline) and resource (current selection), and the op semantics are spelled out precisely. It doesn't explicitly differentiate from siblings like select_region, invert_selection, or deselect, but the operation on an existing selection is reasonably distinct.

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?

The description implies the tool operates on an existing selection ("the current selection") but gives no when-to-use guidance, prerequisites, or alternatives. The note that a border selection 'is how you scope an outline or a contact shadow' hints at usage context without naming or contrasting sibling tools.

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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