slipcover
Near Zero-Overhead Python Code Coverage
Decision gist · record as of 2026-08-14
Yes. SlipCover is worth installing if you need code coverage but have been avoiding it due to performance overhead. It's actively maintained, has no known vulnerabilities, low install friction, and works with modern Python versions (3.9–3.14). The permissive Apache license poses no restrictions. Install it if coverage speed matters to your workflow; skip it only if you have no coverage requirement or are already satisfied with your current tool's performance.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.9 or later; on Python 3.12+ uses sys.monitoring API instead of bytecode rewriting for better efficiency.
- Low install friction with only two runtime dependencies (tabulate and tomli).
- The package is actively maintained with a recent release and no known vulnerabilities, making it straightforward to add to a project.
License · maintenance · safety
permissive license (permissive) — Licensed under Apache Software License (permissive), so you can use, modify, and distribute SlipCover freely in both open-source and commercial projects without significant legal constraints.
last release 2026-08-13 (1 days) · last repo commit 2026-08-14 · 586 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 149,915 downloads/mo, #10,978 on PyPI
Alternatives
Verify before relying
pip install slipcover
python3 -m slipcover myscript.py
# Or with pytest:
python3 -m slipcover -m pytest- Exact overhead reduction compared to Coverage.py on your specific workload (varies by program structure and Python version)
- Whether branch coverage mode is fully stable across all supported Python versions
- Compatibility with other coverage-consuming tools beyond pytest and pytest-xdist
What it is and what it does
SlipCover measures code coverage—which lines and branches of your Python code actually execute during a test run—while keeping runtime overhead near zero. Unlike traditional coverage tools that use Python's tracing API and can double execution time, SlipCover uses just-in-time bytecode instrumentation on Python 3.9–3.11, or the sys.monitoring API on Python 3.12+, to track execution with minimal slowdown. It integrates directly with pytest and other test runners without requiring plugins, and supports configuration via pyproject.toml for per-project settings.
The tool is designed for developers who need coverage data to guide testing, identify dead code, or support fuzzing workflows but can't tolerate the performance penalty of traditional coverage tools. It reports coverage in multiple formats (text, JSON, XML, LCOV) and can merge results from parallel test execution with pytest-xdist.
Use it for
- Measure test coverage on large test suites without doubling execution time, making it practical for continuous integration pipelines.
- Identify untested code paths in performance-critical Python applications where traditional coverage overhead is prohibitive.
- Support property-based testing and fuzzing workflows that require frequent coverage measurements during test generation.
- Find dead code in mature projects by running SlipCover over your full codebase and filtering for zero-coverage modules.
- Enforce coverage thresholds in CI/CD with the fail-under option while keeping build times reasonable.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
SlipCover is worth installing if you need code coverage but have been avoiding it due to performance overhead. It's actively maintained, has no known vulnerabilities, low install friction, and works with modern Python versions (3.9–3.14). The permissive Apache license poses no restrictions. Install it if coverage speed matters to your workflow; skip it only if you have no coverage requirement or are already satisfied with your current tool's performance.
Install
slipcover on PyPI
Before you install
Low install friction with only two runtime dependencies (tabulate and tomli). The package is actively maintained with a recent release and no known vulnerabilities, making it straightforward to add to a project.
Requires Python 3.9 or later; on Python 3.12+ uses sys.monitoring API instead of bytecode rewriting for better efficiency.
License in practice
Licensed under Apache Software License (permissive), so you can use, modify, and distribute SlipCover freely in both open-source and commercial projects without significant legal constraints.
Quickstart
pip install slipcover
python3 -m slipcover myscript.py
# Or with pytest:
python3 -m slipcover -m pytestVerify before relying
- Exact overhead reduction compared to Coverage.py on your specific workload (varies by program structure and Python version)
- Whether branch coverage mode is fully stable across all supported Python versions
- Compatibility with other coverage-consuming tools beyond pytest and pytest-xdist
Package facts
| License | permissive license permissive |
| Python support | Supports the current Python release <3.15,>=3.9 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | 2 packagestabulatetomli |
| Maintenance | Actively maintained 1 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 149,915 / month, #10,978 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | License :: OSI Approved :: Apache Software LicenseOperating System :: MacOS :: MacOS XOperating System :: Microsoft :: Windows :: Windows 10Operating System :: POSIX :: LinuxProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.9 |
Evidence: slipcover-1.1.0-py312-none-any.whl
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