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MalloyTheDev

Aseprite MCP

by MalloyTheDev
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list_slices

Read-only

Retrieve all sprite slices with bounds, pivot, color, and user-data, including parsed JSON, to inspect animation metadata and distinguish unset from set fields.

Instructions

List every slice with its bounds, center, pivot, colour and user-data.

User-data comes back two ways, because it is one string that is sometimes a document.
`data` is the string exactly as Aseprite stores it, so it round-trips through
`set_slice` unchanged. `data_parsed` is added only when that string is valid JSON,
which is the shape worth sending: `{"type": "hitbox", "id": "body"}` is what
`export_slice_metadata` reads a slice's type and id from, and what
`build_asset_from_spec` writes. A slice with no user-data has neither field, so "set
and forgot" and "never set" are now distinguishable, which they were not while this
tool reported the same thing for both.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
filenameYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.10.0
    • removedInput schema / properties / filename / title
      Removed value: -"Filename"
    • removedInput schema / title
      Removed value: -"list_slicesArguments"
  2. First observedv0.7.0

TDQS

A3.9/5.0
Behavior4/5

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

Annotations only declare readOnlyHint and openWorldHint, so the description carries the return-shape burden and does so well: it explains that `data` is the raw stored string, that `data_parsed` is conditionally present only for valid JSON, and that a slice with no user-data has neither field. This 'set and forgot vs never set' distinction is real behavioral context an agent cannot get from the annotations or schema, though ordering/other field formats remain undisclosed.

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?

It is front-loaded with the one-line purpose before any elaboration, and the JSON example earns its place by making the expected payload concrete. The closing clause about prior behavior ('which they were not while this tool reported the same thing for both') is mildly editorial and could be trimmed, but the overall length is justified by the subtle return semantics.

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 and no annotation detail, the description must explain the return value, and it thoroughly covers the hardest part (the two forms of user-data and their conditional presence). It stops short of describing the format of the other returned fields (bounds, center, pivot, colour) or any ordering/pagination, which leaves a small but real gap for a list tool.

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 single parameter is a bare `filename: string` with 0% schema description coverage, and the description adds nothing about it (e.g. whether it is a path, an open sprite, or a project-relative name). The parameter is trivially inferable from sibling conventions, so this is adequate but leaves a real gap given the description otherwise has room to say more.

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 gives a specific verb ('List'), an explicit scope ('every slice'), and enumerates the returned fields (bounds, center, pivot, colour, user-data). This is unmistakably distinct from siblings such as list_sprites or get_sprite_info, and it names the companion tools (set_slice, export_slice_metadata, build_asset_from_spec) that consume the data.

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 usage by explaining that `data` round-trips through `set_slice` and that `data_parsed` is 'the shape worth sending' to `export_slice_metadata`/`build_asset_from_spec', which hints at inspecting slices before exporting. However, it never states an explicit when-to-use or when-not-to-use rule, nor does it point to an alternative inspection tool, so the guidance remains inferred rather than stated.

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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