SVG optimizer in pure MoonBit: svgo-compatible plugin pipeline with path data optimization, colour and number cleanup, and render-diff verification

svg

svgo

optimizer

minifier

wasm

frontend

Download zip

Author

PerfectPan

Version

0.2.1

License

MIT

Repository

github.com/PerfectPan/svgo.mbt

Last updated

1 hour ago

Downloads

#svgo.mbt

An SVG optimizer written in MoonBit, shipped as WebAssembly. All 34 plugins in svgo's preset-default, in its order and with its semantics, and none of the Node.js dependency tree: a 200 KB wasm-gc module that runs in the browser, Node, Bun and Deno, a CLI that installs with npx, and a MoonBit library.

Website & playground · API reference · mooncakes.io · npm @rivus/svgo

#Quickstart

JavaScript (Node 24+, Bun 1.4+, Deno 2, Chrome 130+, Firefox 134+, Safari 18.4+; see Runtime compatibility):

npm i @rivus/svgo

import { optimize } from "@rivus/svgo";
const r = await optimize(svg, { precision: 3 });
r.data; r.originalSize; r.size; r.passes; r.applied;

Command line, without a toolchain (Node 24+; bunx and deno run -A npm:@rivus/svgo work too):

npx @rivus/svgo input.svg -o out.svg
cat input.svg | npx @rivus/svgo > out.svg       # stdin, or pass "-" as the input
npx @rivus/svgo icons -r -o dist                # a directory, recursively
# installed (npm i -g @rivus/svgo) the command is `svgo-mbt`

MoonBit:

moon add PerfectPan/svgo

///|
test "optimize" {
  let result = @svgo.optimize(
    (
      #|<svg xmlns="http://www.w3.org/2000/svg" width="10px" height="10px">
      #|  <!-- Generator: Sketch -->
      #|  <g fill="#FF0000" stroke="none">
      #|    <rect x="0" y="0" width="10.000" height="10.000"/>
      #|  </g>
      #|</svg>
    ),
  )
  inspect(
    result.data,
    content=(
      #|<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"><path fill="red" d="M0 0h10v10H0z"/></svg>
    ),
  )
}

Config provides plugin selection, params : Map[String, Json], precision, multipass, and pretty printing; see the API reference for all fields.

#Command line

svgo-mbt input.svg                            # optimized SVG on stdout
svgo-mbt input.svg -o out.svg --stats         # write a file, print size statistics
svgo-mbt input.svg -p 2 --pretty              # 2 decimal places, indented output
svgo-mbt input.svg --json                     # {data, originalSize, size, passes, applied}
svgo-mbt input.svg --plugins convertPathData,sortAttrs
svgo-mbt input.svg --param cleanupIds.preserve=logo,icon --param cleanupIds.minify=false
svgo-mbt input.svg --disable convertShapeToPath --enable moveGroupAttrsToElems
svgo-mbt --list                               # available plugins

Exit codes: 0 on success, 1 for a usage error, 2 when a file could not be parsed (the names go to stderr, so a shell loop can act on them).

--param <plugin>.<key>=<value> is repeatable. Values true/false become booleans, integers become numbers, comma-separated values become string arrays, and other values remain strings.

#Plugins

Enabled by default, in svgo's preset-default order:

plugin	what it does
removeDoctype, removeXMLProcInst, removeComments, removeMetadata	strip the prolog and editor comments (<!--! ... --> legal comments are kept)
removeEditorsNSData	drop Inkscape / Sketch / Illustrator / Figma namespaces, elements and attributes
cleanupAttrs, removeDesc, cleanupIds, removeUselessDefs	normalise whitespace, drop Created with ... descriptions, unused ids and unreferenced <defs> children
cleanupNumericValues	round numbers, remove px
convertColors	rgb() / names / #RRGGBB to the shortest form
mergeStyles, inlineStyles, minifyStyles	merge <style> elements, inline matching rules to style="...", minify CSS and drop unused selectors
removeUnknownsAndDefaults	drop attributes equal to their defaults, unless an ancestor overrides them
removeDeprecatedAttrs	drop attributes the SVG spec deprecated, keeping the ones that still render
removeNonInheritableGroupAttrs	drop presentation attributes off a <g> that children cannot inherit
removeUselessStrokeAndFill	drop stroke-* when nothing is stroked, fill-* when nothing is filled
cleanupEnableBackground	drop enable-background unless a filter uses BackgroundImage
removeHiddenElems, removeEmptyText	zero-size shapes, display:none, empty paths and texts
convertShapeToPath, convertEllipseToCircle	rect / line / polyline / polygon to path, equal-radius ellipses to circles
moveElemsAttrsToGroup	lift an attribute every child shares onto their group
collapseGroups	unwrap groups and push their attributes down
convertPathData	element transforms baked into the data, curve runs to arcs, relative/absolute per segment, H/V/S/T shorthands, straight curves to lines, precision with drift compensation
convertTransform	multiply, decompose and round transform lists, drop identity and redundant ones
mergePaths	join adjacent paths with identical attributes when their outlines do not intersect
removeEmptyAttrs, removeEmptyContainers, removeUnusedNS, sortAttrs, sortDefsChildren	final cleanup

Optional: removeDimensions, removeTitle, moveGroupAttrsToElems.

Parameters use svgo's names and JSON shapes. Each plugin receives only its own object; omitted fields use these defaults:

Plugin	Parameters and defaults
cleanupIds	remove: true, minify: true, preserve: [], preservePrefixes: [], force: false
convertColors	currentColor: false, names2hex: true, rgb2hex: true, shorthex: true, shortname: true
convertShapeToPath	convertArcs: false, floatPrecision: config precision
convertTransform	floatPrecision: config precision (3), transformPrecision: 5 (limited to matrix precision), degPrecision: derived from matrix digits and float precision
removeComments	preservePatterns: ["^!"]; false or [] removes all comments
removeUnknownsAndDefaults	unknownContent, unknownAttrs, defaultAttrs, uselessOverrides, keepDataAttrs, keepAriaAttrs: all true; keepRoleAttr: false
removeUselessStrokeAndFill	stroke: true, fill: true, removeNone: false
sortAttrs	xmlnsOrder: "front"; order: ["id", "width", "height", "x", "x1", "x2", "y", "y1", "y2", "cx", "cy", "r", "fill", "stroke", "marker", "d", "points"]

preserve and preservePrefixes accept one string or an array of strings. currentColor accepts a boolean or an exact color string and does not replace colors inside masks. preservePatterns supports literal substring matches and ^-prefixed literal prefix matches, not full regular expressions.

#Performance

Same Node process, both with multipass, milliseconds per call (node packages/compare/collect.mjs, Node 24, svgo 4.1.0):

file	size	svgo.mbt (wasm-gc)	svgo-js	ratio
sketch-icon.svg	836 B	0.119	0.319	2.7×
inkscape-drawing.svg	2 KB	0.188	0.669	3.6×
SVG_logo.svg	4 KB	0.579	1.674	2.9×
Tux.svg	50 KB	7.092	14.238	2.0×
Ghostscript_Tiger.svg	68 KB	12.485	36.016	2.9×
World map (low resolution)	85 KB	11.889	51.867	4.4×

Between 1.7× and 4.4× depending on the file, 2.9× at the median. Cold start on a small icon, whole process (scripts/cli-bench.sh): native CLI about 10 ms, Node build about 50 ms, svgo CLI about 160 ms.

#Runtime compatibility

Artifact	Runs on	Checked by
@rivus/svgo (wasm-gc)	Node 24+, Bun 1.4+, Deno 2 (tested with 2.9); Chrome 130+, Firefox 134+, Safari 18.4+	CI runs the 330-case fixture suite through the shipped wasm under Node, Bun and Deno on every push
svgo-mbt CLI, Node build	the same runtimes, via npx / bunx / deno run -A	same suite plus a CLI smoke test
svgo-mbt native binary	linux x86_64, linux arm64, macOS arm64 from GitHub releases; any other platform with moon build --target native --release app/cli	built by binaries.yml on each release
PerfectPan/svgo MoonBit library	targets wasm-gc, js and native; current MoonBit toolchain (CI installs the latest release)	moon test on js and native in CI

The wasm needs an engine with WebAssembly GC and JS String Builtins (imported string constants). Older engines fail at instantiate rather than at runtime: Node 22 and 23 report Import module="_", Bun 1.2 reports import wasm:js-string:length must be an object. This cannot be polyfilled from JavaScript because fromCharCodeArray takes a wasm-gc array. The optimizer itself does no I/O; the loader fetches the wasm over http(s) and reads file: URLs through node:fs, which Bun and Deno provide.

#Compatibility with svgo

Upstream cases (svgo e4cb29b, 2026-08-27):

	cases
pass	289
known differences	0
skipped	0

moveGroupAttrsToElems ships opt-in (--enable moveGroupAttrsToElems). Pushing a group's transform onto its children lets convertPathData bake the matrix into every path, which lengthens coordinates and leaves formerly identical siblings unmergeable. Across the test corpus files it costs 15,859 bytes on the Ghostscript tiger and saves 48 bytes across the rest. svgo shows the same effect on that file (68,101 bytes with the plugin, 52,029 without, against 52,690 for svgo.mbt).

svgo also has 19 opt-in plugins; removeDimensions and removeTitle are implemented, and the other 17 are not.

#Verification

scripts/verify.sh            # check, fmt, .mbti drift, fixtures, tests on js / native
scripts/verify.sh --full     # + wasm build, sizes vs svgo-js, resvg pixel diff, speed (needs pnpm install)

Runs unit tests, svgo's own fixture suite, resvg pixel diff, and byte-for-byte corpus checks. Details and developer guides: docs/ARCHITECTURE.md, CONTRIBUTING.md, AGENTS.md.

#License

MIT. Plugin semantics follow svgo (MIT, © Kir Belevich and contributors).

UnknownPlugin

source

pub suberror UnknownPlugin {
  UnknownPlugin(String)
} derive(@moonbitlang/core/debug.Debug
Debug)

Raised by optimize when Config::plugins names a plugin that does not exist.

impl Show for UnknownPlugin

Config

source

pub(all) struct Config {
  plugins : Array[String]
  params : Map[String, Json]
  precision : Int
  multipass : Bool
  pretty : Bool
} derive(@moonbitlang/core/debug.Debug
Debug)

What to run and how to print: the plugin list in execution order, numeric precision, multipass and pretty printing. Start from Config::default() and override fields with record update syntax.

Config::default

source

fn Config::default() -> Config

svgo's preset-default plugins in svgo's order (except the opt-in moveGroupAttrsToElems), 3 decimal places, multipass on, compact output.

Result

source

pub(all) struct Result {
  data : String
  original_size : Int
  size : Int
  passes : Int
  applied : Array[String]
} derive(@moonbitlang/core/debug.Debug
Debug)

Outcome of optimize: the optimized document plus size statistics and the list of plugins that changed something.

Result::saved_percent

source

fn Result::saved_percent(self : Result) -> Double

Bytes saved as a percentage of the original size (0 for an empty input).

list_plugins

source

fn list_plugins() -> Array[(String, String, Bool)]

Names of all available plugins with their descriptions.

optimize

source

fn optimize(svg : String, config? : Config) -> Result raise

Optimize an SVG document.

Source Files

svgo.mbt

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svgo

#svgo.mbt

#Quickstart

#Command line

#Plugins

#Performance

#Runtime compatibility

#Compatibility with svgo

#Verification

#License

#UnknownPlugin

#Config

#Config::default

#Result

#Result::saved_percent

#list_plugins

#optimize

Source Files

UnknownPlugin

Config

Config::default

Result

Result::saved_percent

list_plugins

optimize