wheelgap

Find the Python dependencies that have no prebuilt wheel for your target platform, before your Docker build does.

Point it at your lockfile and the platforms you ship to (ARM servers, Alpine images, Windows on ARM, free-threaded Python 3.14t). It tells you which packages pip or uv will have to compile from source, and which can't be installed at all.

📊 New: wheel coverage for the top 5,000 PyPI packages, by platform and Python version, updated nightly.

Install and run (under 30 seconds)

With uv:

uvx wheelgap

Or with pipx:

pipx run wheelgap

Or install it: pip install wheelgap.

Run either one in a project directory. It finds uv.lock, pylock.toml, poetry.lock, pdm.lock, Pipfile.lock, requirements.lock or requirements.txt on its own.

Usage

See the recipes for a free-threading readiness report you can use in scripts.

# Will my Alpine ARM image compile anything?
wheelgap -p 3.13 -t alpine-arm64

# Is my stack ready for free-threaded Python 3.14?
wheelgap -p 3.14t -t all

# Several Pythons at once, Linux on both architectures
wheelgap uv.lock -p 3.12,3.13,3.14 -t linux-x86_64,linux-aarch64

# No -p? A .python-version file next to uv.lock (written by uv or pyenv) sets the Python
wheelgap uv.lock -t linux-x86_64

# Check a Pipenv project's default and development dependencies
wheelgap Pipfile.lock -p 3.13 -t linux-x86_64,linux-aarch64

# Check a PDM project's locked distribution files
wheelgap pdm.lock -p 3.13 -t linux-x86_64,linux-aarch64

# No lockfile? Check packages directly (latest version, or pin one)
wheelgap psycopg2 uvloop numpy==2.3.4 -t windows,win-arm64

# Take the target from the final stage's image (e.g. python:3.13-alpine
# or ghcr.io/astral-sh/uv:0.13.7-python3.13-trixie-slim), following
# named stages like `FROM base AS runtime` back to the image they start from.
# A python X.Y tag without a Debian release (python:3.13-slim) is read as
# the release Docker Hub currently builds it on (trixie, glibc 2.41, for 3.9
# and later); patch tags like 3.12.7-slim keep the --glibc default. Pin
# -bookworm or -trixie for an answer that doesn't move
wheelgap --dockerfile Dockerfile

# Machine-readable, for scripts and CI
wheelgap --json > wheelgap.json

# Why is it a gap? List each rejected wheel and the reason
wheelgap -t alpine-arm64 --explain

Projects usually ship to the same platforms, so you can write the defaults down once in pyproject.toml (next to the lockfile, or in the current directory). Command-line flags still win.

[tool.wheelgap]
python = ["3.13", "3.14t"]
targets = ["linux-x86_64", "linux-aarch64", "musl-aarch64"]
glibc = "2.31"

Each cell in the table is one of:

Packages that are fine everywhere are hidden; --all shows them.

--explain lists, for each gap, the wheels that were rejected and why, closest misses first:

armlib 1.4.0 on musl-aarch64: ● source
  armlib-1.4.0-cp313-cp313-manylinux_2_17_aarch64.manylinux2014_aarch64.whl  manylinux_2_17_aarch64 is a glibc wheel; musl (Alpine) needs musllinux

For uv.lock inputs, --explain also shows why the package is installed at all: the shortest dependency path from your project (or from a dependency group, shown as (dev group)) to the gap package. Paths are worked out per target, since markers can pull a package in on one platform only. With --json --explain, each package gets a matching via object keyed by target, like rejected: "via": {"win-arm64": ["myapp", "uvicorn", "uvloop"]}. Other inputs have no dependency graph, so they show no path (and "via": {}).

In --json output, results, rejected and via are all keyed by target label: just the platform ("linux-x86_64") when one Python is checked, or Python and platform ("3.13 linux-x86_64") with several. The top-level targets list gives each target's label, python and platform, so a script can look the key up instead of building it:

import json

data = json.load(open("wheelgap.json"))
key = next(t["label"] for t in data["targets"] if t["python"] == "3.13" and t["platform"] == "linux-x86_64")

uvloop 0.21.0 on win-arm64: ● source
  via: myapp → uvicorn → uvloop

If you think wheelgap got a package wrong, that output (or --json --explain) is all a bug report needs, with no need to share your lockfile.

Exit codes: 0 no gaps, 1 gaps found, 2 bad input. --exit-zero always exits 0. --fail-on missing (or fail-on = "missing" in [tool.wheelgap]) accepts source builds and only exits 1 when a package can't be installed at all.

If an input can't be read (a missing lockfile, an unknown target, a bad [tool.wheelgap] value), --json prints {"error": {"message": "...", "type": "TargetError"}} on stdout instead of results, next to the usual wheelgap: error: line on stderr and exit code 2. Command-line usage errors from argparse are still plain text on stderr.

Use --ignore psycopg2 for accepted gaps (repeatable or comma-separated, with case-insensitive package-name matching and equivalent hyphens, underscores and dots): matched packages are excluded from the table, counts and exit status, and listed as ignored in text (including quiet mode), JSON and Markdown. Set ignore = ["psycopg2"] in [tool.wheelgap] to use it by default; any --ignore flags replace the configured list rather than adding to it, and --ignore "" clears it for one run.

Use -q / --quiet (or quiet = true in [tool.wheelgap]) to show only the gap summary and package names. Clean runs without ignored packages are silent, JSON and Markdown output are unchanged, and quiet text output cannot be combined with --explain (--json --explain and --markdown --explain work).

Targets

Run wheelgap --list-targets to see target aliases and compatibility limits, or add --json for a machine-readable list.

If you know the deployment distro rather than its libc version, use --distro:

wheelgap uv.lock -p 3.13 -t linux-aarch64 --distro ubuntu-22.04
wheelgap uv.lock -p 3.13 -t musl-aarch64 --distro alpine

It supplies a glibc or musl version only: it does not select Python versions or platforms. Keep using -t for those platforms, including musl-* for Alpine. You can also set distro = "ubuntu-22.04" in [tool.wheelgap].

For each libc, an explicit --glibc / --musl wins, then --distro, then a version from --dockerfile, then a glibc / musl config value, then the config distro, then the built-in default. A distro only supplies its own libc; the other libc keeps its existing default. Names are case-insensitive; unknown names are errors. For older Alpine, pass --musl 1.1 explicitly. The text --list-targets output also lists distro names; its JSON output remains a list of platforms.

Only x86 Linux takes manylinux wheels older than glibc 2.17: every other architecture's first manylinux was manylinux2014 (glibc 2.17), so pip accepts nothing older there, and neither does wheelgap.

iOS and Android (PEP 730 and PEP 738, Python 3.13+) are checked with -t mobile or by name, for apps built with tools like BeeWare's Briefcase. Mobile dependencies are installed by a cross-platform pip run that can only use wheels, so a package with only an sdist shows as ✗ missing. --ios and --android-api (or ios = "15.0" and android-api = 28 in [tool.wheelgap]) set your app's minimum iOS version and Android API level. wheelgap checks PyPI only: Briefcase and Chaquopy also install from their own package repositories (BeeWare's on anaconda.org, and chaquo.com), which have mobile builds of packages like numpy, so a ✗ missing there may still install.

Pyodide (Python in the browser) only installs wheels: there's no compiler, so a package with only an sdist shows as ✗ missing, not ● source. Pyodide wheels are tied to one ABI per Python version and don't work across them. Pyodide also ships its own builds of many popular packages (numpy, pydantic-core and others) that aren't on PyPI. Point --pyodide-lock at the release's pyodide-lock.json (a path or https:// URL, also pyodide-lock = "..." in [tool.wheelgap]) and those count as ✓ bundled, with a note when Pyodide's version differs from the one you pinned:

wheelgap -p 3.12 -t pyodide --pyodide-lock https://cdn.jsdelivr.net/pyodide/v0.27.7/full/pyodide-lock.json

Docker platform names also work with -t, for example -t linux/amd64,linux/arm64 (also linux/arm64/v8, linux/arm/v7, linux/ppc64le, linux/s390x and linux/riscv64).

-t all checks the eight common native platforms, and -t everything adds the armv7l, ppc64le, s390x and riscv64 Linux targets (glibc and musl). Pyodide, iOS and Android are only checked when you name them. Python versions take a trailing t for free-threaded builds (3.14t), which correctly rejects abi3 wheels. Without -p, wheelgap reads a .python-version file next to the lockfile (or pyproject.toml) if there is one, and otherwise uses the Python it is running on.

In CI (GitHub Action)

- uses: actions/checkout@v7
- uses: wheelgap/wheelgap@v0.8.0
  with:
    args: uv.lock -p 3.13 -t linux-x86_64,linux-aarch64

The job fails when a dependency would build from source on a target you ship, for example when a dependency bump drops ARM wheels. The gap table also goes to the run's summary page (set summary: false to turn that off).

Outside the Action, --markdown prints the same report as Markdown, for a job summary (wheelgap --markdown >> "$GITHUB_STEP_SUMMARY") or a PR comment. With --explain, the rejected wheels go in a collapsed section.

With pre-commit

repos:
  - repo: https://github.com/wheelgap/wheelgap
    rev: v0.8.0
    hooks:
      - id: wheelgap

The hook runs when uv.lock, poetry.lock, pdm.lock, pylock.toml, Pipfile.lock, or a requirements*.txt or requirements*.lock file changes. Put your targets in [tool.wheelgap] in pyproject.toml so the hook checks the right platforms. Pass extra options with args:, for example args: [--fail-on, missing].

From Python

import wheelgap

targets = wheelgap.make_targets(python="3.13", platforms=["linux-aarch64", "musl-aarch64"])

result = wheelgap.check_package("numpy", "2.3.4", targets)  # looks the files up on PyPI
result.ok  # True if every target has a wheel
result.gaps  # the targets that don't
result.to_dict()  # {"name": ..., "results": {"3.13 musl-aarch64": "wheel", ...}}

for r in wheelgap.check_lockfile("uv.lock", targets):  # markers and the uv graph respected
    print(r.name, r.version, [t.platform for t in r.gaps])

check_packages([...]) checks many packages in parallel, and check_package(..., files=[...]) works offline from filenames you already have.

Scanning the top PyPI packages

python -m wheelgap.scan --top 5000 --out coverage.json

This checks the latest release of the most-downloaded packages (from top-pypi-packages) against the eight common platforms (and Pyodide), for Python 3.13, 3.14, 3.14t, 3.15 and 3.15t by default, and writes one JSON file with per-platform totals. It's the data behind the coverage tracker on the roadmap.

With an AI coding agent

wheelgap ships a check-wheels skill that teaches coding agents to run it, read its JSON and suggest fixes. It follows the open Agent Skills format.

Claude Code (install from this repository as a plugin):

/plugin marketplace add wheelgap/wheelgap
/plugin install wheelgap@wheelgap

On Claude Code 2.1.275 or later, /plugin install wheelgap --marketplace wheelgap/wheelgap does both in one step.

Codex, Cursor, GitHub Copilot and others: copy integrations/claude-code/skills/check-wheels/ into your project's .agents/skills/ folder. For a Cursor project rule instead, copy integrations/cursor/wheelgap.mdc to .cursor/rules/.

Contributing to wheelgap with an agent? See AGENTS.md.

How it works

• Lockfiles are read offline. uv.lock, pylock.toml, poetry.lock and pdm.lock already record every file published for each pinned version (except a uv.lock or pylock.toml whose requires-python leaves out the Python you check; see below). wheelgap parses the wheel filenames' tags with packaging and checks them against the exact tag set each target accepts. That is the same logic pip and uv use to pick a wheel.
• requirements.txt, requirements.lock and bare package names are looked up on the PyPI JSON API. Feed it a fully pinned file (from Rye, uv pip compile, pip-compile or uv export): wheelgap checks the lines you give it and doesn't resolve dependencies. Rye's default (non-universal) locks are resolved for the machine that created them and carry no platform markers.
• Pipfile.lock reads default, develop and any custom package categories (such as docs or tests) and looks up distribution filenames on PyPI for their pinned versions. Environment markers are preserved; Git, path, file and editable dependencies are skipped as non-index packages. Packages pinned to an index that isn't PyPI are skipped too (private index), so their names aren't sent to pypi.org. A PyPI mirror counts as a private index here, since wheelgap can't tell it apart from an internal one.
• Environment markers are respected. A pywin32 ; sys_platform == 'win32' dependency won't show up as a Linux gap. For uv.lock the dependency graph is walked per target, so transitive platform-specific packages are handled too.
• --online re-checks lockfile packages against PyPI. Packages the lock says came from another index keep their locked files, so their names are never sent to PyPI. Use it when a project has uploaded new wheels for an existing version since you locked, or if your uv.lock was generated with environments restrictions. A uv.lock or pylock.toml whose requires-python leaves out a target's Python (say ==3.13.*, checked with -p 3.14t) may be missing wheels for it, because uv only keeps the wheels that can serve requires-python. Without --online, wheelgap then also looks up its PyPI packages on the index, keeps the lock's own files if a lookup fails, and prints a note (with -q, only when some packages couldn't be re-checked).

Why this exists

Missing wheels show up late, in the most expensive place:

• Your python:3.13-alpine image on an ARM runner takes 25 minutes because two transitive dependencies don't publish musllinux_aarch64 wheels, and QEMU is compiling them.
• A build fails with error: Microsoft Visual C++ 14.0 or greater is required on a teammate's Snapdragon laptop.
• You try free-threaded Python 3.14t and half your stack quietly falls back to source builds, because abi3 wheels don't apply there.

Sites like pyreadiness.org and free-threaded wheels track the top few hundred packages. wheelgap checks your packages, at your pinned versions, for your targets, in about a second, and it can run in CI.

Roadmap

wheelgap is growing into caniuse for Python wheels: an open map of which packages have wheels for which platforms. The CLI stays focused, and around it come a nightly tracker of the most-used PyPI packages, a community knowledge base of workarounds, and campaigns to help upstream projects ship missing wheels. Read the roadmap and join the discussion →

Next up for the CLI, each with a first step written up and no PR yet:

• "nearest version with a wheel" hints (#20)
• wheelgap diff: the new gaps between two lockfiles, for PR comments (#51)
• caching index lookups between runs (#65)
• version ranges: picking the newest release that supports each target's Python (#84)

The roadmap and help wanted labels have more.

Contributing

Contributions are welcome, and pull requests usually get a review within hours.

• New here? Issues labelled good first issue say which files to change and what to test.
• Done one or two? help wanted issues are bigger, and a good next step.

CONTRIBUTING.md has the 3-command dev setup, or you can start in the browser with no setup:

Questions are welcome in Discussions.

Thanks

wheelgap is created and maintained by @patrickballard, with a lot of help from these people. Thank you, all of you!

License

MIT