SVG Polish

A fast, lossless, type-safe SVG optimizer for Python.

svg_polish shrinks SVG files — strips editor metadata, collapses redundant attributes, dedups gradients, optimises path data and transforms — while guaranteeing that the output renders identically to the input. The library is fully typed (py.typed), thread-safe, secure-by-default against XML attacks, and ships with a single short API: optimize().

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Why SVG Polish

Before	After
style="fill:#ff0000;stroke:#000000"	fill="#f00"
Inkscape / Sketch / Adobe namespaces	Removed
Verbose path commands	Collapsed and rounded
Duplicate gradients	Deduplicated
Hostile XXE / billion-laughs payload	Rejected before parsing

Install

Requires Python 3.10+.

pip install svg-polish

The install is pure Python and depends only on defusedxml. A svg-polish[fast] extra is reserved for the v1.x lxml-backed XML engine (~3–5× faster on large files); v1.0 ships only the defusedxml.minidom backend.

Quick start

Python

from svg_polish import optimize

optimized = optimize('<svg xmlns="http://www.w3.org/2000/svg">…</svg>')

That's the whole pitch. Read from disk, write to disk:

from pathlib import Path
from svg_polish import optimize, optimize_path

with open("input.svg", encoding="utf-8") as f:
    svg = f.read()

optimized = optimize(svg)

with open("output.svg", "w", encoding="utf-8") as f:
    f.write(optimized)

# or, in one line via the path-aware helper:
Path("output.svg").write_text(optimize_path("input.svg"), encoding="utf-8")

Pass OptimizeOptions for tuning:

from svg_polish import optimize, OptimizeOptions

opts = OptimizeOptions(
    digits=3,
    shorten_ids=True,
    enable_viewboxing=True,
    strip_comments=True,
)
optimized = optimize(svg, opts)

For metrics, use optimize_with_stats:

from svg_polish import optimize_with_stats

result = optimize_with_stats(svg)
print(f"saved {result.saved_bytes} B ({result.saved_ratio:.1%}) in {result.duration_ms:.1f} ms")

For async web frameworks:

from svg_polish import optimize_async

async def handler(svg: str) -> str:
    return await optimize_async(svg)

Command line

svg-polish -i input.svg -o output.svg
cat input.svg | svg-polish > output.svg
svg-polish -i input.svg -o output.svgz       # gzip-compressed output

Aggressive settings:

svg-polish -i input.svg -o output.svg \
  --enable-viewboxing \
  --enable-id-stripping \
  --enable-comment-stripping \
  --shorten-ids \
  --indent=none

Run svg-polish --help for the full flag list.

Public API

Symbol	Purpose
optimize(svg, options=None)	Canonical entry point. Alias of optimize_string.
optimize_string(svg, options=None)	str/bytes in, str out.
optimize_bytes(svg, options=None)	bytes in, UTF-8 bytes out.
optimize_path(path, options=None)	Read from a filesystem path.
optimize_async(svg, options=None)	await-able wrapper via asyncio.to_thread.
optimize_with_stats(svg, options=None)	Returns an OptimizeResult with metrics.
OptimizeOptions	Frozen dataclass — the only configuration shape.
OptimizeResult	Optimised SVG + stats + duration.
ScourStats	Per-pass counters.

Exceptions: SvgPolishError (base) → SvgParseError, SvgPathSyntaxError, SvgTransformSyntaxError, SvgOptimizeError, SvgSecurityError, InvalidOptionError. See docs/api.md for the full reference.

What it does

• Removes editor metadata (Inkscape, Sodipodi, Illustrator, Sketch).
• Strips default attribute values and empty attributes.
• Converts colors to the shortest equivalent form.
• Deduplicates <linearGradient> / <radialGradient> definitions.
• Collapses <g> wrappers and merges sibling groups.
• Optimises <path> d data (relative coords, h/v/s shortcuts, segment merging).
• Optimises transform, patternTransform, gradientTransform.
• Reduces numeric precision to a configurable digit count.
• Optionally shortens IDs, strips comments, converts to viewBox, embeds rasters.
• Custom serialiser produces tight, deterministic output.

All passes are lossless by default — see docs/performance.md for the opt-in decimal_engine="float" mode that trades reproducibility for ~3-5× faster numeric arithmetic.

Security

Inputs are parsed through defusedxml, so XML external entity attacks, billion-laughs, and external DTD fetches are rejected before they touch the optimiser. Inputs over 100 MB are refused by default. See SECURITY.md for the threat model and docs/security.md for usage patterns.

Documentation

• docs/api.md — Python API reference.
• docs/architecture.md — module layout, layering, pipeline.
• docs/performance.md — tuning guide and benchmarks.
• docs/security.md — usage patterns for untrusted input.
• docs/cli.md — command-line reference.
• docs/configuration.md — OptimizeOptions field-by-field.

Development

git clone https://github.com/g-battaglia/svg_polish.git
cd svg_polish
uv sync

uv run poe test          # full test suite (~660 tests)
uv run poe test-cov      # with coverage HTML report
uv run poe lint          # ruff lint
uv run poe format        # ruff format
uv run poe typecheck     # mypy strict
uv run poe check         # all of the above

uv run poe bench         # save a performance baseline
uv run poe bench-compare # compare current run against the baseline

Origin

svg_polish is a fork of Scour, originally created by Jeff Schiller and Louis Simard in 2010, later maintained by Tobias Oberstein and Patrick Storz. Upstream Scour has been dormant since August 2021. This v1.0 release is a ground-up modernisation:

• Python 3.10+ only; no six, no Python 2 compatibility shims.
• Single typed public surface (OptimizeOptions, OptimizeResult, optimize_*).
• Modular passes (one file per transformation) instead of a 4 700-line monolith.
• Thread-safe Decimal precision contexts.
• Secure-by-default XML parsing with defusedxml.
• 100% line coverage, mypy --strict clean, ruff clean.

License

Apache License 2.0 — see LICENSE.

svg_regex.py is derived from code by Enthought, Inc. (BSD 3-Clause). Full attribution in NOTICE.