Haskell, finally fast.
One opinionated, batteries-included toolchain for Haskell.
Fast, unified, futuristic.
Haskell's tooling is powerful — and scattered. Starting a project means juggling ghcup, cabal, stack, fourmolu, hlint, and hpc, each with its own flags, config, and failure modes.
hx collapses all of it into a single, fast binary. Written in Rust, it drives the tools you already trust behind one coherent interface — with deterministic builds, errors that tell you how to fix them, and a feedback loop quick enough to stay out of your way.
One command to install. One file to configure. One tool to learn.
- Batteries included — Build, test, run, format, lint, profile, and publish. Watch mode, coverage reports, and IDE setup. Everything in one tool.
- Managed toolchains — Automatic GHC installation and per-project version pinning in
hx.toml. No ghcup required. - Deterministic builds — TOML lockfiles with fingerprint verification. Reproducible across machines and CI — correct by construction, not by luck.
- Excellent errors — Actionable messages with fix suggestions.
hx doctordiagnoses your setup and tells you exactly what to do. - Drop-in compatible — Works with existing
.cabalfiles and Hackage. Import from Stack or Cabal — your workflow stays the same, just better. - Extensible — Plugin system with Steel (Scheme), pre/post-build hooks, and Nix integration.
- Agent-ready — A built-in MCP server (
hx mcp), an AGENTS.md, and a Claude skill let AI agents drive the whole toolchain. - Blazingly fast — Native builds bypass Cabal overhead: ~5.6× faster cold builds, ~7.8× faster incremental.
- Futuristic — A first-class BHC backend: a next-generation Haskell compiler with curated Platform snapshots.
# macOS/Linux
curl -fsSL https://arcanist.sh/hx/install.sh | sh
# Or download from releases
https://github.com/arcanist-sh/hx/releaseswinget install raskell-io.hx
cargo install --git https://github.com/arcanist-sh/hx hx-clihx --version
hx doctor# Create a new project
hx init myapp
cd myapp
# Build and run
hx build
hx run
# Lock dependencies for reproducibility
hx lock
hx sync
# Watch for changes
hx watchhx init # Initialize in current directory
hx init myapp # Create myapp/ and initialize
hx init --lib # Create a library project
hx init --ci # Include GitHub Actions workflow
hx new webapp myapp # Create web app (Servant)
hx new cli myapp # Create CLI app (optparse-applicative)
hx new library mylib # Create library with docs setup
hx new template <url> <name> # Create from git templatehx build # Build the project (all packages in a workspace)
hx build --package mylib # Build a single workspace member
hx build --release # Build with optimizations
hx build --native # Use native GHC build (no cabal)
hx build -j4 # Parallel build with 4 jobs
hx check # Fast type-check
hx clean # Clean build artifactsWorkspaces — For a
cabal.projectwith several local packages,hx buildandhx testbuild and test every member. Use--package <name>to target a single member.
hx run # Build and run the executable
hx run -- arg1 arg2 # Pass arguments to the program
hx repl # Start an interactive GHCi session
hx test # Run tests (all packages in a workspace)
hx test --package mylib # Test a single workspace member
hx test --pattern "Unit" # Filter tests by pattern
hx bench # Run benchmarkshx watch # Auto-rebuild on file changes
hx watch --test # Auto-run tests on changes
hx watch --clear # Clear terminal between runshx lock # Generate/update hx.lock
hx lock --update # Update all dependencies
hx sync # Build with locked dependencies
hx fetch # Pre-fetch dependencies in parallel
hx add text # Add a dependency
hx add aeson ">=2.0" # Add with version constraint
hx add --dev hspec # Add dev dependency
hx rm text # Remove a dependency
hx why text # Show why a package is a dependency
hx info aeson # Show package details from Hackage
hx info aeson --versions # Include all available versions
hx outdated # Check for outdated dependencies
hx outdated --direct # Only show direct dependencies
hx update # Update dependencies (minor/patch)
hx update --major # Allow major version updates
hx update --dry-run # Preview updates without applying
hx update aeson text # Update specific packages
hx tree # Show dependency tree
hx tree --depth 2 # Limit tree depth
hx list # List all dependencies
hx list --direct # List direct dependencies only
hx deps graph --format dot # Generate Graphviz graph (also: tree, list, json)
hx search aeson # Search Hackage for packages
hx audit # Check for deprecated dependencies
hx audit --outdated # Check for outdated packageshx fmt # Format code with fourmolu
hx fmt --check # Check formatting without changes
hx lint # Run hlint
hx lint --fix # Apply automatic fixeshx coverage # Run tests with coverage
hx coverage --html # Generate HTML report
hx coverage --html --open # Generate and open in browser
hx coverage --threshold 80 # Fail if below 80% coverage
hx coverage --json # Output JSON for CIhx profile # Run with time profiling
hx profile --heap # Run with heap profiling
hx profile --time --heap # Both time and heaphx docs # Generate documentation
hx docs --open # Generate and open in browser
hx docs --deps # Include dependency docs
hx docs --serve # Serve locally on port 8080hx toolchain status # Show installed versions
hx toolchain list # List all available versions
hx toolchain list --installed # List installed versions only
hx toolchain install 9.8.2 # Install GHC version
hx toolchain install --set # Install and set as active
hx toolchain install --bhc <version> # Install the BHC toolchain
hx toolchain remove 9.6.4 # Remove a GHC version
hx toolchain use 9.8.2 # Switch GHC version
hx toolchain use project # Use project's toolchain
hx stackage list # List Stackage snapshots
hx bhc-platform list # List BHC Platform snapshots
hx server start # Start the persistent build server
hx server status # Show build server statushx ide setup # Generate hie.yaml for HLS
hx ide status # Check IDE configuration
hx lsp # Start language server
hx mcp # Start an MCP server for AI agents (JSON-RPC/stdio)hx mcp exposes build/test/run/lock/doctor/dependency tools over the
Model Context Protocol. See
AGENTS.md for how to drive hx from an AI agent, the Claude skill at
.claude/skills/hx/SKILL.md for slash-command
workflows, and the llms.txt project map
(served at arcanist.sh/hx/llms.txt) for a compact, agent-friendly overview.
hx publish # Publish to Hackage
hx publish --dry-run # Validate without uploading
hx publish --docs # Include documentation
hx changelog # Generate CHANGELOG from commits
hx changelog --preview # Preview without writinghx dist # Build release archive
hx dist --target x86_64-unknown-linux-musl # Cross-compile
hx dist formula # Generate Homebrew formula
hx dist install-script # Generate install scripthx doctor # Diagnose setup issues
hx script file.hs # Run single-file script
hx import --from cabal # Import a Cabal project (cabal.project or bare .cabal)
hx import --from stack # Import from stack.yaml
hx nix flake # Generate flake.nix
hx nix shell # Generate shell.nix
hx completions install # Auto-install completions for your shell
hx completions generate bash # Generate completions to stdout
hx upgrade # Upgrade hx to latest versionhx import --from cabal works with a full cabal.project or just a bare
.cabal file — in the latter case the directory is adopted as a single-package
project. hx import --from stack adopts an existing Stack project. Running a
project command outside an hx project but inside a Cabal or Stack project
reports "project not found" and suggests hx import to adopt it.
hx cache status # Show cache statistics
hx cache artifacts # Show artifact cache statistics
hx cache prune --days 30 # Remove entries older than 30 days
hx cache clean # Clear entire cache
hx index update # Update Hackage package index
hx index clear # Remove the local index
hx index status # Show index statushx plugins list # List available plugins
hx plugins status # Show plugin system status
hx plugins run script.scm # Run a Steel script
hx plugins trust # Allow this project's local plugins to run
hx plugins untrust # Revoke that permissionProject-local plugins (.hx/plugins/*.scm) only run after you trust the
project with hx plugins trust - cloning a repository never grants its
scripts execution rights.
hx uses hx.toml for project configuration:
[project]
name = "myapp"
kind = "bin" # or "lib"
resolver = "cabal"
[toolchain]
ghc = "9.8.2"
cabal = "3.12.1.0"
hls = "2.9.0.0"
[build]
optimization = 2 # 0, 1, or 2
warnings = true
native = false # Use native GHC builds
[format]
formatter = "fourmolu"
[lint]
hlint = true
[plugins]
enabled = true
hook_timeout_ms = 30000
[plugins.hooks]
pre_build = ["./scripts/check.scm"]
post_test = ["./scripts/notify.scm"]hx supports global configuration at ~/.config/hx/config.toml (Linux), ~/Library/Application Support/hx/config.toml (macOS), or %APPDATA%\hx\config\config.toml (Windows).
Global settings provide defaults that can be overridden by project-local hx.toml:
# ~/.config/hx/config.toml
[toolchain]
ghc = "9.8.2"
cabal = "3.12.1.0"
[build]
optimization = 1
warnings = true
[format]
formatter = "fourmolu"
[lint]
hlint = truehx config show # Show current global configuration
hx config path # Show path to global config file
hx config edit # Open config file in your $EDITOR
hx config init # Create default config file
hx config set <key> <val> # Set a configuration value
hx config get <key> # Get a configuration value
# Examples:
hx config set toolchain.ghc 9.8.2
hx config set build.optimization 2
hx config set format.formatter ormoluThe hx.lock file ensures reproducible builds:
version = 1
created_at = "2026-01-16T00:00:00Z"
[toolchain]
ghc = "9.8.2"
cabal = "3.12.1.0"
[plan]
compiler_id = "ghc-9.8.2"
platform = "x86_64-linux"
hash = "sha256:..."
[[packages]]
name = "text"
version = "2.1.1"The native solver evaluates .cabal conditionals (os, arch, impl(ghc),
and flag) and excludes dependencies of disabled components (buildable: False),
so platform- and compiler-specific packages never leak into the lockfile.
Single-package projects (including bare .cabal adoptions) get a real lockfile
too, so hx why, hx deps, and hx outdated work there as well.
Packages with a custom Setup.hs (build-type: Custom) build correctly via
delegation to Cabal.
| Variable | Description |
|---|---|
HX_VERBOSE |
Enable verbose output |
HX_QUIET |
Suppress output |
HX_NO_COLOR |
Disable colored output |
HX_CONFIG_FILE |
Path to config file |
HX_CACHE_DIR |
Cache directory location |
HX_AUTO_INSTALL |
Auto-install missing toolchains |
HX_NO_AUTO_INSTALL |
Never auto-install toolchains |
HX_ALLOW_UNVERIFIED_DOWNLOADS |
Allow toolchain installs without a published checksum |
HX_BHC_PLATFORM_PUBKEY |
Pinned Ed25519 key for BHC Platform snapshot verification |
| Code | Meaning |
|---|---|
| 0 | Success |
| 1 | General error |
| 2 | Usage error |
| 3 | Configuration error |
| 4 | Toolchain error |
| 5 | Build/test failure |
| 6 | Plugin hook failure |
hx is a Rust workspace with these crates:
| Crate | Purpose |
|---|---|
hx-cli |
Command-line interface |
hx-core |
Shared types and utilities |
hx-config |
Configuration parsing |
hx-lock |
Lockfile management |
hx-toolchain |
GHC/Cabal detection and installation |
hx-cabal |
Cabal wrapper and native builds |
hx-cache |
Build cache management |
hx-doctor |
Diagnostic checks |
hx-solver |
Native dependency resolver |
hx-lsp |
Language server protocol |
hx-plugins |
Steel plugin runtime |
hx-ui |
Terminal output utilities |
hx-warnings |
Warning system |
hx-telemetry |
Tracing and metrics |
hx-compiler |
Compiler backend abstraction (GHC, BHC) |
hx-bhc |
BHC (Basel Haskell Compiler) native build pipeline |
# Build
cargo build
# Run tests
cargo test --workspace
# Run clippy
cargo clippy --workspace -- -D warnings
# Format
cargo fmt
# Run hx locally
cargo run -p hx-cli -- --helphx follows the Astral playbook — earn trust by improving what exists before replacing any of it:
- Wrap first — Drive the tools you already rely on (GHC, Cabal) instead of reimplementing them.
- Tame second — Layer on better UX, error messages, and workflows until the rough edges disappear.
- Replace last — Swap in faster paths (native builds) and a next-generation compiler (BHC) only where they earn their place.
The destination: a Haskell toolchain that's fast, unified, and futuristic — without asking you to throw away what already works.
MIT — part of arcanist.sh.