Cellar
CLI tool for coding agents and developers to query the public API of any Maven JVM dependency — get symbol signatures, list packages, search by name, and inspect dependency trees. Powered by Coursier and tasty-query.
Install / Use
/learn @VirtusLab/CellarREADME
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
Download the native binary for your platform from https://github.com/simple-scala-tooling/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
# 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:
--moduleis required (e.g.--module lib,--module core) - scala-cli:
--moduleis 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 tree |
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 |
| --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, search | Max results (default: 50) |
Output conventions
- stdout — Markdown content (signatures, docs, source)
- stderr — diagnostics (warnings, truncation notices)
- Exit 0 — success
- Exit 1 — error
Example output
<details> <summary><code>cellar get-external org.typelevel:cats-core_3:2.10.0 cats.Monad</code></summary>## 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]
...
```
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.
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
Add the following to your project's CLAUDE.md to teach Claude Code how to use cellar:
## 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
Tech stack
Scala 3, Cats Effect, fs2, tasty-query, Coursier, decline, Mill.
