SLSA (Supply-chain Levels for Software Artifacts) is a security framework and specification of progressive levels for hardening software build and release pipelines. It defines requirements and provenance attestations to prevent tampering.
SLSA
SLSA (Supply-chain Levels for Software Artifacts, pronounced “salsa”) is a security framework that defines progressive levels for hardening how software is built and released. Originating at Google and now stewarded under the OpenSSF, it gives teams a common language for describing how tamper-resistant a build pipeline is and what evidence backs that claim. The point is to make the path from source to published artifact verifiable, not just trusted.
- Progressive levels - A tiered model (roughly Build L1 through L3) where each level demands stronger guarantees against tampering.
- Provenance attestations - Signed, machine-readable metadata describing exactly how, where, and from what an artifact was built.
- Build integrity - Requirements for isolated, scripted builds that resist a single compromised developer or workstation.
- Ecosystem-neutral - A framework meant to layer onto existing CI/CD systems rather than replace them.
For APIs, SLSA is most relevant to the packages, containers, and gateway components that make up an API platform, where a compromised build is a direct path to a compromised production surface. Provenance attestations fit naturally alongside other supply-chain signals in governance — the same instinct behind security.txt and SBOM adoption — as machine-checkable evidence of operational maturity. As build and release pipelines increasingly involve automated agents, verifiable provenance becomes the way to trust what those pipelines produce.
Open source tools that implement this standard
Harvested from this standard's own governing organisation, with the license read from each repository rather than assumed. The role is what the tool does to the specification, from the shared vocabulary — so an agent holding one of these documents can resolve straight from a goal to a tool.
| Tool | Role | License | What it does |
|---|---|---|---|
| SLSA GitHub Generator | attests |
Apache-2.0 | Generates SLSA provenance for artifacts built in GitHub Actions, using reusable workflows that produce non-forgeable attestations. |
| Witness | attests |
Apache-2.0 | Wraps any build command and produces a signed in-toto attestation about what it observed — the materials, the products, and the... |
| SLSA Verifier | verifies |
Apache-2.0 | Verifies SLSA provenance against expectations — that an artifact came from the source repository and builder it claims. |
| SLSA Source Tool | attests |
Apache-2.0 | A proof-of-concept implementation of the SLSA Source Track, attesting to source-side controls. |
