Cellar

Look up the public API of any JVM dependency from the terminal.

---

When a coding agent needs to call an unfamiliar library method, its options are bad: parse HTML docs (expensive, unreliable), find source on GitHub (requires knowing the URL), or hallucinate the API.

Cellar gives agents — and humans — a single shell command that returns exactly the type signatures, members, and docs needed to write correct code. Output is plain Markdown on stdout, ready to be injected into an LLM prompt with zero post-processing.

Supported artifacts

Format	Support
Scala 3 (TASTy)	Full — signatures, flags, companions, sealed hierarchies, givens, extensions, docstrings
Scala 2 (pickles)	Best-effort — type information may be incomplete
Java (.class)	Good — signatures, members

Installation

Nix

Run without installing:

nix run github:VirtusLab/cellar -- get-external org.typelevel:cats-core_3:2.10.0 cats.Monad

Install into your profile:

nix profile install github:VirtusLab/cellar

A Nix overlay is also available at github:VirtusLab/cellar#overlays.default.

Manual

Download the native binary for your platform from https://github.com/VirtusLab/cellar/releases/latest, then extract and install:

tar xz -f cellar-*.tar.gz
sudo mv cellar /usr/local/bin/

To verify checksums and signatures, see RELEASING.md.

Quick start

# Look up a trait from cats
cellar get-external org.typelevel:cats-core_3:2.10.0 cats.Monad

# Look up a symbol from the current project
cellar get --module core cats.Monad

# List top-level symbols in a package
cellar list-external org.typelevel:cats-core_3:2.10.0 cats

# Search for a method name
cellar search-external org.typelevel:cats-core_3:2.10.0 flatMap

# View source code
cellar get-source org.typelevel:cats-core_3:2.10.0 cats.Monad

# Dependency tree
cellar deps org.typelevel:cats-effect_3:3.5.4

Commands

Cellar has two modes: project-aware commands that work against your current project's classpath, and external commands that query arbitrary Maven coordinates.

Project-aware commands

Run from your project root. Cellar auto-detects the build tool (Mill, sbt, or scala-cli), extracts the classpath, and queries your project's code and all its dependencies.

cellar get [--module <name>] <fqn>
cellar list [--module <name>] <package>
cellar search [--module <name>] <query>

• Mill / sbt: --module is required (e.g. --module lib, --module core)
• scala-cli: --module is not supported — omit it

The classpath is cached after the first run. Use --no-cache to force re-extraction.

External commands

Query any published Maven artifact by explicit coordinate:

cellar get-external <coordinate> <fqn>
cellar list-external <coordinate> <package>
cellar search-external <coordinate> <query>
cellar get-source <coordinate> <fqn>
cellar deps <coordinate>

Command reference

Command	Description
get	Symbol info from the current project (signature, flags, members, docs)
get-external	Symbol info from a Maven coordinate
get-source	Source code from a published -sources.jar
list	List public symbols in a package/class from the current project
list-external	List public symbols from a Maven coordinate
search	Case-insensitive substring search in the current project
search-external	Case-insensitive substring search from a Maven coordinate
deps	Print the transitive dependency list

Maven coordinates

Coordinates use the format group:artifact:version. The :: shorthand is not supported — use the full artifact name.

org.typelevel:cats-core_3:2.10.0        # Scala 3
org.typelevel:cats-core_2.13:2.10.0     # Scala 2
org.apache.commons:commons-lang3:3.14.0 # Java

Use latest as the version to automatically resolve the most recent release:

cellar get-external org.typelevel:cats-core_3:latest cats.Monad

Options

Flag	Applies to	Description
--module <name>, -m	project commands	Build module name (required for Mill/sbt)
--no-cache	project commands	Skip classpath cache, re-extract from build tool
--config <path>, -c	project commands	Path to config file
--java-home <path>	all	Use a specific JDK for JRE classpath
-r, --repository <url>	external commands	Extra Maven repository URL (repeatable)
-l, --limit <N>	list, list-external, search, search-external	Max results (default: 50)

Configuration

Cellar loads configuration from HOCON files and environment variables. Files are loaded in order, with later values overriding earlier ones:

1. Built-in defaults
2. ~/.cellar/cellar.conf (user-level, optional)
3. .cellar/cellar.conf (project-level, optional)

Use --config <path> / -c <path> to load a specific file instead.

Default config

mill {
  # Binary to invoke when extracting Mill classpaths
  binary = "./mill"           # env: CELLAR_MILL_BINARY
}

sbt {
  # Binary to invoke when extracting sbt classpaths (e.g. "sbt", "sbtn")
  binary = "sbt"              # env: CELLAR_SBT_BINARY
  # Extra arguments passed to sbt, space-separated (e.g. "--client")
  extra-args = ""             # env: CELLAR_SBT_EXTRA_ARGS
}

Examples

Use sbtn instead of sbt:

sbt { binary = "sbtn" }

Use sbt in --client mode:

sbt { extra-args = "--client" }

Use a custom Mill wrapper:

mill { binary = "./millw" }

Or via environment: CELLAR_SBT_BINARY=sbtn cellar get --module core cats.Monad

Output conventions

• stdout — Markdown content (signatures, docs, source)
• stderr — diagnostics (warnings, truncation notices)
• Exit 0 — success
• Exit 1 — error

Example output

cellar get-external org.typelevel:cats-core_3:2.10.0 cats.Monad

## cats.Monad
```scala
trait Monad[F] extends FlatMap[F] with Applicative[F]
```
Monad.
Allows composition of dependent effectful functions.

**Flags:** abstract
**Origin:** cats.Monad
**Members:**
```scala
def flatMap[A, B](fa: F[A])(f: Function1[A, F[B]]): F[B]
def pure[A](x: A): F[A]
def flatten[A](ffa: F[F[A]]): F[A]
def iterateWhile[A](f: F[A])(p: Function1[A, Boolean]): F[A]
...
```

cellar list-external org.typelevel:cats-core_3:2.10.0 cats --limit 5

object Eval$
trait ComposedContravariantCovariant[F, G] extends Contravariant[TypeLambda]
object Later$
object Show$
trait EvalSemigroup[A] extends Semigroup[Eval[A]]
Note: results truncated at 5. Use --limit to increase.

cellar search-external org.typelevel:cats-core_3:2.10.0 flatMap --limit 3

cats.FlatMap — object FlatMap$
cats.FlatMap — trait FlatMap[F] extends Apply[F] with FlatMapArityFunctions[F]
cats.FlatMap$ — object FlatMap$
Note: results truncated at 3. Use --limit to increase.

Using cellar with Claude Code

As a plugin (recommended)

Install cellar as a Claude Code plugin for auto-updates:

/plugin marketplace add virtuslab/cellar
/plugin install cellar@cellar

Claude will automatically have access to the /cellar:cellar skill and know when to use it.

Manual setup

Alternatively, add the following to your project's CLAUDE.md:

## Cellar

When you need the API of a JVM dependency, use cellar. Always prefer cellar over hallucinating API signatures.

### Project-aware commands (run from project root)

For querying the current project's code and dependencies (auto-detects build tool):

    cellar get [--module <name>] <fqn>       # single symbol
    cellar list [--module <name>] <package>  # explore a package
    cellar search [--module <name>] <query>  # find by name

- Mill/sbt projects: `--module` is required (e.g. `--module lib`, `--module core`)
- scala-cli projects: `--module` is not supported (omit it)
- `--no-cache`: skip classpath cache, re-extract from build tool
- `--java-home`: override JRE classpath

### External commands (query arbitrary Maven coordinates)

For querying any published artifact by explicit coordinate:

    cellar get-external <coordinate> <fqn>       # single symbol
    cellar list-external <coordinate> <package>  # explore a package
    cellar search-external <coordinate> <query>  # find by name
    cellar get-source <coordinate> <fqn>         # source code
    cellar deps <coordinate>                     # dependency tree

Coordinates must be explicit: `group:artifact_3:version` (use `latest` for newest version).

### Workflow

1. **Don't know the package?** → `cellar search <query>` or `cellar search-external <coordinate> <query>`
2. **Know the package, not the type?** → `cellar list <package>` or `cellar list-external <coordinate> <package>`
3. **Know the type?** → `cellar get <fqn>` or `cellar get-external <coordinate> <fqn>`
4. **Need the source?** → `cellar get-source <coordinate> <fqn>`

Building from source

Requires JDK 17+ and Mill.

# Fat JAR
./mill cli.assembly
java -jar out/cli/assembly.dest/out.jar get-external org.typelevel:cats-core_3:2.10.0 cats.Monad

# Native image (GraalVM)
./mill cli.nativeImage

# Wrapper script (for development)
./scripts/cellar get-external org.typelevel:cats-core_3:2.10.0 cats.Monad

Running tests

# Publish test fixtures to local Maven first
./mill publishFixtures

# Run tests
./mill lib.test

Installing a local build with Nix

./mill cli.nativeImage && nix profile install --impure .#dev

Tech stack

Scala 3, Cats Effect, fs2, tasty-query, Coursier, decline, Mill.

License

MPL-2.0