osslili — OSS License & Copyright Detector

osslili reads source code and tells you which licenses it carries and who holds the copyright. It identifies licenses against the full SPDX list, extracts copyright statements, and reports where every finding came from.

It is built for license compliance work, where the question is usually "what am I allowed to do with this, and how do I know". Every detection is traceable to the file and method that produced it, and osslili does not assert a license it cannot substantiate — an identification it cannot back up is dropped rather than guessed at.

Documentation: semclone.github.io/osslili

Installation

pip install osslili

Requires Python 3.9 or later.

Recommended: install python-tlsh alongside it.

pip install osslili python-tlsh

It is optional, but detection is measurably better with it. It powers the fuzzy matching tier, which identifies license texts too reformatted for exact or similarity matching — several licenses are detectable only this way — and corroborates borderline similarity matches so they can be reported at all. Without a corroborator that band stays closed, because accepting an unverified match there means reporting one license as another it merely resembles, and copyleft and permissive licenses are often a single clause apart.

python-tlsh builds from C and needs a compiler; on slim container images run apt-get install -y gcc python3-dev first.

For development:

git clone https://github.com/SemClone/osslili.git
cd osslili
pip install -e ".[dev]"

Quick start

# Declared license of a project — license files, metadata, README
osslili .

# Everything, including license headers embedded in source
osslili --deep .

# SBOM output
osslili -f cyclonedx-json -o sbom.json .

{
  "scan_results": [
    {
      "path": ".",
      "license_evidence": [
        {
          "file": "/path/to/project/package.json",
          "detected_license": "MIT",
          "confidence": 1.0,
          "detection_method": "tag",
          "category": "declared",
          "match_type": "package_metadata",
          "description": "Package metadata declares MIT license"
        },
        {
          "file": "/path/to/project/LICENSE",
          "detected_license": "MIT",
          "confidence": 0.997,
          "detection_method": "dice-sorensen",
          "category": "declared",
          "match_type": "license_file",
          "description": "License file contains MIT license"
        }
      ]
    }
  ]
}

Scanning modes

Default mode answers "what does this project declare". Deep mode finds license headers embedded in code and vendored third-party files, and is considerably slower.

How detection works

Each file goes through several independent passes — package metadata, SPDX tags, keyword matching, and a four-tier full-text cascade:

Detections are not collapsed to a single answer — agreement between independent methods is itself evidence. Each carries a category (declared, detected, referenced, third-party) and a confidence score.

Licenses found in bundled third-party notice files are categorized separately, so a vendored THIRD_PARTY_NOTICES file does not make a permissive project look copyleft.

See Detection for the full picture, including why the fuzzy tier verifies its own candidates before reporting them.

Library usage

from osslili import LicenseCopyrightDetector

detector = LicenseCopyrightDetector()
result = detector.process_local_path("/path/to/source")

primary = result.get_primary_license()
if primary:
    print(f"{primary.spdx_id} ({primary.confidence:.0%} via {primary.detection_method})")

# The project's own licenses, excluding bundled third-party notices
for license in result.get_own_licenses():
    print(license.spdx_id, license.category, license.source_file)

for copyright in result.copyrights:
    print(copyright.statement)

# Output formats
evidence = detector.generate_evidence([result], detail_level="full")
kissbom = detector.generate_kissbom([result])
sbom = detector.generate_cyclonedx([result], format_type="json")

Configuration

osslili -c osslili.yaml .

similarity_threshold: 0.97
max_recursion_depth: 4
thread_count: 4
cache_dir: ~/.cache/osslili
custom_aliases:
  "My Company License": "LicenseRef-MyCompany"

Every option is documented at Configuration.

Documentation

Full documentation is at semclone.github.io/osslili.

• Overview — what osslili does, installing, first run
• Usage — scanning modes, every flag, output formats
• Detection — how licenses are identified, reading confidence and category
• Python API — using osslili as a library
• Configuration — config file schema and all options
• SPDX data — refreshing the bundled license list

The pages are built from docs/ in this repository, so corrections can go straight into a pull request.

Contributing

We welcome contributions! Please see CONTRIBUTING.md for details on:

• Code of conduct
• Development setup
• Submitting pull requests
• Reporting issues

Support

• GitHub Issues — bug reports and feature requests
• Documentation — complete project documentation

License

Apache License 2.0 — see LICENSE file for details.

Authors

See AUTHORS.md for a list of contributors.

Part of the SEMCL.ONE ecosystem for comprehensive OSS compliance and code analysis.