Hermeto

A CLI tool that pre-fetches your project's dependencies for hermetic, network-isolated container builds and produces accurate SBOMs from the pre-fetched dependencies.

Without network isolation, builds can silently pull tampered packages, produce unreproducible artifacts, or accidentally hide dependencies in your audit trail. Hermeto closes that gap.

When Hermeto fits

Hermeto is opinionated by design. Your build process must be:

• Defined: Hermeto only fetches dependencies explicitly declared in your project, typically in a lockfile or equivalent input file
• Reproducible: every dependency, including transitive ones, must be pinned to an exact version. Hermeto does not resolve dependencies on its own
• Secure: when your package manager supports expected checksums, declare them so Hermeto can verify downloads against supply-chain tampering

Prerequisites: a git repository with committed lockfiles and a container runtime (Podman or Docker) to run Hermeto and to build in network isolated environment.

Hermeto is not for you if your build resolves or fetches dependencies over the network at compile time — Hermeto requires all dependencies to be declared and pinned up front.

Supported package managers

Dedicated backends read your project's existing lockfiles. Without one, the generic fetcher can pre-fetch arbitrary URLs, but you must create and maintain the artifacts.lock.yaml file yourself.

• Go: gomod
• Java: maven (experimental)
• JavaScript: npm, pnpm, yarn (classic and berry)
• Python: pip
• Ruby: bundler
• Rust: cargo
• Other: rpm, generic

What Hermeto provides

• Accurate SBOMs: generates CycloneDX v1.6 or SPDX v2.3 manifests covering every prefetched dependency
• No arbitrary code execution: dependencies are fetched without running untrusted code, keeping the build supply chain safe
• Configurable: tunable via YAML config files or HERMETO_ environment variables (see docs/configuration.md)

Quick start

Hermeto is distributed as a container image ghcr.io/hermetoproject/hermeto — it is not a standalone PyPI package. Pull the image and optionally set up an alias:

alias hermeto='podman run --rm -ti -v "$PWD:$PWD:z" -w "$PWD" ghcr.io/hermetoproject/hermeto:latest'

The typical workflow has four steps:

1. Pre-fetch dependencies

hermeto fetch-deps \
  --source ./my-repo \
  --output ./hermeto-output \
  '{"path": ".", "type": "gomod"}'  

The output directory will contain the downloaded dependencies and a generated SBOM. For multiple packages in one repo, pass a JSON array or point to a JSON input file.

2. Generate environment variables

hermeto generate-env ./hermeto-output -o ./hermeto.env --for-output-dir /tmp/hermeto-output

Produces a shell-sourceable env file that tells your package manager where to find the cached dependencies.

3. Inject project files

hermeto inject-files ./hermeto-output --for-output-dir /tmp/hermeto-output

Some package managers need configuration files or lockfile adjustments: this step applies them to your source tree automatically.

4. Build with network isolation

podman build . \
  --volume "$(realpath ./hermeto-output)":/tmp/hermeto-output:Z \
  --volume "$(realpath ./hermeto.env)":/tmp/hermeto.env:Z \
  --network none \
  --tag my-app

Inside the Dockerfile, run . /tmp/hermeto.env before your package manager commands.

Merging SBOMs

When you fetch dependencies for multiple packages separately, merge the results with hermeto merge-sboms sbom_1.json sbom_2.json -o merged.json.

Contributing

We welcome contributions — whether that's filing issues, suggesting features, or submitting code. Check out CONTRIBUTING.md to get started and AI_CONTRIBUTION_POLICY.md if you plan to use AI-assisted tooling.

Please follow our CODE_OF_CONDUCT.md and report security issues via SECURITY.md.

Hermeto is released under the GPL-3.0-only license.