Introduction

jdx is an IDE for AI agents, as a command line tool. It answers the questions an IDE answers for a human — what members a class has, what a method does, who calls it, what implements an interface, what an upgrade breaks — for any JVM jar, Maven coordinate, class or source directory, and the JDK itself.

Why it exists#

An agent working on a Java or Kotlin codebase constantly needs to know things about code it cannot see: the library jars on the classpath and the JDK. Without jdx it pieces the answers together with unzip, javap, grep and by reading thousand-line source files into its context window. That is slow, noisy, and burns the context the agent needs for the actual task.

jdx replaces each of those multi-step hunts with one command that returns one precise answer:

$ jdx show java.util.HashMap
class java.util.HashMap
  public class HashMap
  extends java.util.AbstractMap
  implements java.util.Map, java.lang.Cloneable, java.io.Serializable
  members: 4 constructors, 52 methods, 13 fields
source: java.base (jrt)
next: jdx members java.util.HashMap --inherited

Real output — this example ran against the current jdx when the page was built.

Every answer names its symbols canonically and suggests the next command (next:), so an agent moves from question to question by copy-paste instead of reconstruction.

What it can answer#

Question	Command	IDE gesture
What is this type?	`jdx show`	Go to declaration
What can I call on it?	`jdx members`	Code completion after `.`
What does this method do?	`jdx body`	Open the method
What does the javadoc say?	`jdx doc`	Quick documentation
Who uses this?	`jdx usages`	Find usages
Who implements this?	`jdx hierarchy`, `jdx implementors`	Type hierarchy
Who calls this, what does it call?	`jdx callers`, `jdx calls`	Call hierarchy
How is it used in practice?	`jdx samples`	(no IDE equivalent)
What does this upgrade break?	`jdx diff`	(no IDE equivalent)

The command catalogue lists all of them.

Design principles#

These are product guarantees, not aspirations — each is enforced by tests:

Minimal correct output. Bounded by default, never a file dump when a member was asked for. Truncation is explicit and says which flag shows the rest.
Never guesses. An ambiguous reference exits 2 and lists every candidate as a copy-pasteable reference. Guessing wrong is worse than asking.
Provenance on every answer. Which jar, whether the text came from sources, bytecode or a decompiler — and which one — so the agent can judge confidence.
Deterministic. Same inputs, byte-identical output. No timestamps, no absolute paths.
Meaningful exit codes, so agents branch without parsing prose (details).
Degrade, don't fail. No sources jar? It decompiles — and labels the result as reconstructed.
Read-only. Bytecode is parsed with ASM; inspected classes are never loaded, so no code from the jars you inspect ever runs.

Where to go next#

Install jdx (one command, JDK 21+).
Run the quickstart — five minutes against the JDK and a Maven library.
Connect your AI agent over MCP or the CLI.