Nettle

Nettle (NETlist Traversal and Topology Layout Explorer) turns elaborated Verilog and SystemVerilog into a portable .nettle bundle and opens it as an interactive schematic in a web browser. Use it to understand synthesized RTL connectivity, navigate or selectively flatten hierarchy, cross-probe source and schematic objects, and share a reviewable snapshot without sharing a compiler environment.

Nettle deliberately separates its portable bundle from viewing. The native CLI runs standalone Slang and Yosys with yosys-slang to normalize a design into a versioned ZIP + Protobuf bundle. Opening a local bundle still validates and renders it entirely in browser memory without uploading it. An optional private-cloud service adds explicit bundle sharing and queued server-side compilation without changing that local workflow.

Try the public demo

The GitHub Pages deployment at https://xlsynth.github.io/nettle hosts the browser viewer with two public examples: the RTL Bedrock CDC FIFO used by the browser regression and Nettle's schematic diff fixture. You can also open a local .nettle file; local files are read and rendered entirely in the browser and are never uploaded. The demo is a static viewer, not a hosted HDL compiler, and its bundled examples (including their sources) are public.

Demo

The demo builds br_counter.nettle from the manifest-pinned upstream br_counter.sv design and starts the viewer at http://127.0.0.1:8090.

Run all commands from the repository root.

First prepare the demo corpus. This clones Bedrock-RTL, sparse-checks out the full Git SHA in integration_tests/bedrock-rtl/manifest.json, and keeps the upstream sources under the ignored target/ directory:

scripts/check-design-corpus.py --prepare-only --corpus bedrock-rtl \
  --workspace target/design-corpora

Build and view with the combined image

The combined Nettle image is the recommended quickstart. It is Linux/amd64 because the pinned HDL compiler toolchain does not publish a Linux/arm64 archive. render leaves the generated bundle in the mounted checkout and serves it until you stop the foreground container.

docker run --rm --platform linux/amd64 \
  -p 127.0.0.1:8090:8080 \
  -v "$PWD:/work" -w /work \
  ghcr.io/xlsynth/nettle:latest render \
  --filelist target/design-corpora/bedrock-rtl/br_counter.f \
  --project-root target/design-corpora/bedrock-rtl \
  --top br_counter \
  --output br_counter.nettle

Open http://127.0.0.1:8090 while the container runs. Do not open http://0.0.0.0:8080: it is the container's bind address, not a browser URL. Browsers treat it as an insecure origin and disable the Web Crypto API Nettle uses to validate bundles.

On Docker Engine for Linux, add --user "$(id -u):$(id -g)" to keep the output bundle owned by the calling user. The same command works with podman in place of docker; add --userns=keep-id:uid=10001,gid=10001 and mount the checkout with :Z when SELinux relabeling is required.

Build the combined image locally

Build the nettle target, then use nettle:latest in place of ghcr.io/xlsynth/nettle:latest in the command above. First record the build metadata from the checkout:

NETTLE_BUILD_DATE_UTC="$(date -u +%Y-%m-%dT%H:%M:%SZ)"
NETTLE_BUILD_GIT_SHA="$(git rev-parse HEAD)"
if [ -n "$(git status --porcelain --untracked-files=normal)" ]; then
  NETTLE_BUILD_STATE=dirty
elif ! git for-each-ref --contains HEAD --format='%(refname)' \
  refs/heads/main refs/remotes |
  grep -Eq '(^refs/heads/main$|^refs/remotes/.+/main$)'; then
  NETTLE_BUILD_STATE=dev
else
  NETTLE_BUILD_STATE=clean
fi
export NETTLE_BUILD_DATE_UTC NETTLE_BUILD_GIT_SHA NETTLE_BUILD_STATE

Pass those values into the image build:

docker build --platform linux/amd64 \
  --build-arg NETTLE_BUILD_DATE_UTC \
  --build-arg NETTLE_BUILD_GIT_SHA \
  --build-arg NETTLE_BUILD_STATE \
  -f Dockerfile --target nettle -t nettle:latest .

Container image

Nettle publishes one Linux/amd64 image, ghcr.io/xlsynth/nettle, with the compiler toolchain, static viewer, and hosted service. Use build, view, render, or host according to the workflow you need.

Run without containers

This path builds and runs Nettle directly on the host. First install the native system dependencies, then verify the HDL compiler toolchain and build Nettle and its static viewer:

scripts/check-toolchain.sh
cargo build --locked
npm ci
npm run build

Build and view the demo bundle:

cargo run --locked -- render \
  --filelist target/design-corpora/bedrock-rtl/br_counter.f \
  --project-root target/design-corpora/bedrock-rtl \
  --top br_counter \
  --output br_counter.nettle \
  --web-root web/dist \
  --port 8090

Open http://127.0.0.1:8090; Nettle opens br_counter.nettle directly. Press Ctrl-C in the terminal to stop the viewer.

Development

With containers

See Build the combined image locally for the interactive image build command. To run the complete test suite in its known-good toolchain container, record and export the same build metadata, then build the root Dockerfile's test target:

docker build --platform linux/amd64 \
  --build-arg NETTLE_BUILD_DATE_UTC \
  --build-arg NETTLE_BUILD_GIT_SHA \
  --build-arg NETTLE_BUILD_STATE \
  -f Dockerfile --target test -t nettle-test .

Native system requirements

Native development works on any host where the required compiler tools are available. On Linux/amd64, the versions below match the known-good container. On macOS/arm64 or Linux/arm64, install or build native host versions of Slang and Yosys with yosys-slang; the pinned standalone Slang Linux release is amd64-only. Install:

• Rust 1.88 or newer. This checkout selects and validates Rust 1.95.0 through rust-toolchain.toml.
• standalone Slang 11 or newer. Slang 11.0 is the known-good release. Nettle checks for the command-file, top selection, JSON diagnostics/AST, define, undefine, and parameter capabilities it uses.
• Yosys with a compatible yosys-slang plugin. Nettle does not claim a numeric Yosys/plugin version range because the two components must be a compatible pair; it probes read_slang and every required plugin capability before compiling. The OSS CAD Suite snapshot dated 2026-06-15 is known good.
• Node.js 20.19 or later in the 20.x line, 22.12 or later in the 22.x line, or 24 or newer, plus npm to build the web viewer. Node.js 24 with npm 11 is the known-good configuration.
• A modern web browser to use the viewer. Chromium is additionally required to run the browser end-to-end tests.

The Dockerfile is the source of truth for known-good toolchains and build environments. Its builder, test, and nettle targets record the exact Slang release/source commit and checksums, the checksummed OSS CAD Suite artifact, and the Rust and Node image versions. Nettle never downloads HDL compilers at runtime. Run scripts/check-toolchain.sh after installing native compiler tools to exercise their capabilities end to end.

Install the locked JavaScript dependencies and build the static viewer:

npm ci
npm run build

Cargo uses the committed Cargo.lock; use --locked for reproducible native builds. A typical local development cycle is:

scripts/check-toolchain.sh
cargo build --locked
cargo test --locked
npm test
npm run dev

The development viewer is then available at http://127.0.0.1:5173. Use cargo build --locked --release for an optimized native binary.

Usage

Run commands from the repository root unless noted otherwise.

Build and view a bundle

Build the included counter:

cargo run --locked -- build \
  --filelist target/design-corpora/bedrock-rtl/br_counter.f \
  --project-root target/design-corpora/bedrock-rtl \
  --top br_counter \
  --output br_counter.nettle

The project root defaults to the filelist's parent. Set a wider root when a filelist reaches sources through ..; every embedded source must canonicalize inside that boundary. Nettle embeds only referenced UTF-8 sources up to 4 MiB and records project-relative paths.

Start the built static viewer and select the bundle in its file picker:

cargo run --locked -- view --web-root web/dist --port 8090

Then open http://127.0.0.1:8090. The browser reads the selected file; the static host never receives it. For frontend development, npm run dev serves the application at http://127.0.0.1:5173.

Pass a bundle to open it directly:

cargo run --locked -- view br_counter.nettle --web-root web/dist --port 8090

This copies the bundle into a private, size-bounded anonymous temporary snapshot, validates that exact copy, and exposes it at a fixed, non-cacheable route. Anonymous storage has no pathname to orphan and is reclaimed by the operating system when its final handle closes, including after abrupt process termination. Keep the default loopback bind for sensitive designs. A non-loopback bind makes the bundle downloadable by reachable clients and therefore requires the deployment's normal authentication and TLS protections.

render combines build and view while leaving the bundle on disk:

cargo run --locked -- render \
  --filelist target/design-corpora/bedrock-rtl/br_counter.f \
  --project-root target/design-corpora/bedrock-rtl \
  --top br_counter \
  --output br_counter.nettle \
  --web-root web/dist \
  --port 8090

Run the hosted web and compiler service

nettle host serves three explicitly separate workflows from one process:

1. open a local .nettle entirely inside the browser without uploading it;
2. upload and persist a prebuilt .nettle, then view or download it through a shareable capability URL; or
3. upload a source archive, wait in the FIFO build queue, and persist, view, or download the resulting .nettle.

Source uploads default to project.f at the archive root. The upload dialog can instead select any root filelist by its relative archive path, such as br_counter/filelist.f; nested filelists and every declared project path are validated beneath the extracted archive root before compilation.

The hosted service runs Slang and Yosys as child processes in the same container. It does not launch nested containers or create Kubernetes workloads. The v1 deployment is exactly one Pod and one container.

For local evaluation, give the combined image a persistent session volume and a bounded scratch filesystem:

docker run --rm --platform linux/amd64 \
  --read-only --cap-drop ALL --security-opt no-new-privileges \
  -p 127.0.0.1:8080:8080 \
  -v nettle-sessions:/data \
  --tmpfs /scratch:rw,nosuid,nodev,noexec,size=4g \
  ghcr.io/xlsynth/nettle@sha256:REPLACE_WITH_PUBLISHED_DIGEST host \
  --storage-root=/data \
  --scratch-root=/scratch \
  --max-queued-builds=32 \
  --build-timeout=600s \
  --evict-after=30d

Loopback HTTP is suitable only for local evaluation. A shared deployment must terminate HTTPS and restrict reachability to its intended private-cloud user group. Nettle does not authenticate individual users; group authentication at the ingress is optional and site-dependent. Capability URLs are bearer secrets: anyone who can reach the service and has a session URL can view and download its bundle. The UI repeats this fact and the configured retention period before either upload.

The checked-in deploy/kubernetes.yaml is the recommended private-cloud starting point. It runs a single non-root replica with Recreate, a PVC backed by the site's encrypted StorageClass, bounded ephemeral scratch, a read-only root filesystem, dropped capabilities, no service-account token, and no outbound network. It intentionally leaves cluster-specific TLS, network access, optional group authentication, hostname, StorageClass, and image digest configuration to the admin. See deploy/README.md for setup and operational details.

Compare two elaborated designs

Build the reference and candidate as independent snapshots, then open schematic diff mode:

cargo run --locked -- compare reference.nettle candidate.nettle \
  --matching conservative \
  --web-root web/dist \
  --port 8090

The command copies and validates both inputs in anonymous delete-on-close storage before starting the viewer and exposes the private snapshots only through separate non-cacheable startup routes. The two snapshots can consume up to twice the configured per-bundle temporary-storage ceiling; the operating system reclaims them when their final handles close, including after abrupt termination. The default conservative policy accepts exact and uniquely determined graph correspondence. Pass --matching aggressive, or switch policy in the viewer, to distinguish heuristic matches for logic whose compiler-generated identities changed.

The viewer constructs one union graph and lays it out once: reference-only objects are red and dashed, candidate-only objects are green, matched changes are yellow, and unchanged logic remains neutral. Line, outline, and subtle shadow treatments distinguish diff status and heuristic correspondence. The single View menu selects a neutral reference or candidate snapshot, the complete diff overlay, changes-only presentation, or custom status visibility; every view reuses the union geometry. Matching is a structural review aid, not a functional- equivalence result.

Hierarchy navigation and flattening use the same selected policy. Recursive flattening compares child modules before splicing their union through paired boundaries, including one-sided instances, and a policy change recomputes the visible projection. Decoded children are reused while they remain in the bounded provider caches; evicted modules may be decoded again.

The left pane compares the UTF-8 compilation sources embedded in the two bundles. This is intentionally a bundled source diff, not a complete Git tree diff: files not included in either snapshot and version-control rename metadata are unavailable. Different defines, parameters, tops, or compiler versions are reported separately because they can change the elaborated graph without changing source text. Diff hunks are labeled source-only only after neither direct source origins nor indirect evidence anywhere in the reachable paired hierarchy connects them to a schematic change; selecting a graph-affecting hunk highlights every directly intersecting object in the visible overlay.

Parameters, defines, and configuration files

Builder overrides are repeatable, raw single-line SystemVerilog expressions:

cargo run --locked -- build \
  --filelist project.f \
  --project-root "$PWD" \
  --top top \
  --param WIDTH=16 \
  --define SYNTHESIS \
  --define NUM_HARTS=4 \
  --undefine SIMULATION \
  --output design.nettle

Duplicate names, empty values, invalid identifiers, and define/undefine conflicts are rejected before compilation. Add --debug-artifacts only when raw Yosys JSON, Slang AST JSON, and compiler transcripts are needed; those artifacts can reveal substantially more project detail.

Larger builds can use YAML:

# build.yaml
filelist: filelists/project.f
project_root: .
top: top
output: design.nettle
parameters:
  DEPTH: "32"
  WIDTH: "16"
defines:
  NUM_HARTS: "4"
  SYNTHESIS: null
undefines:
  - SIMULATION
debug_artifacts: false

cargo run --locked -- build --config build.yaml

YAML paths are relative to the configuration file; command-line paths are relative to the current directory. YAML may also set slang_bin and yosys_bin. Scalar CLI values override YAML values, while parameter, define, and undefine collections are combined. Quote expressions and macro values so YAML preserves them as strings. Unknown fields are rejected. See INPUT_CONFIG_FILE_FORMAT.md for the complete schema and merge behavior.

Inspect and validate bundles

cargo run --locked -- inspect design.nettle
cargo run --locked -- validate design.nettle

inspect prints safe summary metadata. validate checks archive membership, resource limits, hashes, Protobuf payloads, source indexes, and module index/body consistency without extracting files. See NETTLE_FILE_FORMAT.md for the normative schema and compatibility rules.

Viewer containers and deployment

The unified image can serve the static viewer for existing bundles on linux/amd64:

docker run --rm --platform linux/amd64 -p 127.0.0.1:8090:8080 \
  ghcr.io/xlsynth/nettle:latest

On Apple silicon hosts, --platform linux/amd64 selects the published image architecture.

In a shared deployment, place the static site behind the normal authentication and HTTPS boundary. Design bytes selected with the file picker remain in each user's browser. Use the combined image and deploy/kubernetes.yaml only when upload, persistence, or server-side compilation is wanted.

Validation

scripts/check-rust-docs.py
cargo fmt --all --check
RUSTDOCFLAGS="-D warnings" cargo doc --no-deps --locked
cargo test --locked
cargo clippy --all-targets --all-features --locked
npm run lint
npm test
npm run build
npm run check:deployment
npm run test:e2e
scripts/check-toolchain.sh
npm run test:designs

The real-toolchain design regressions are opt-in because they require the external HDL compilers. The Development section shows how to run the complete suite in the known-good container environment.

Project documentation

• ARCHITECTURE.md describes the software architecture, trust boundaries, data flow, and tool design.
• NETTLE_FILE_FORMAT.md defines the .nettle interchange format and its security rules.
• INPUT_CONFIG_FILE_FORMAT.md defines the YAML build configuration schema and command-line merge behavior.
• RESOURCE_LIMITS_FILE_FORMAT.md documents the build-time resource-limit policy shared by the native and browser code.
• deploy/README.md documents the single-Pod hosted-service deployment and its private-cloud responsibilities.

License

Nettle is licensed under the Apache License 2.0.

Integration tests indirectly use third-party repositories that are referenced by manifests. Third-party sources are not committed into this repository. Nevertheless, manifests identify third-party provenance and applicable license and notice files.