jvmsrc — Give your coding agent a Java IDE

An MCP server and CLI that gives your coding agent the one thing it's missing on JVM codebases: the actual classpath.

The Problem

You use an IDE to write Java. Your coding agent doesn't have one.

When your agent hits an unfamiliar library type — say, a superclass from a proprietary internal library — it spends 25+ turns walking ~/.gradle/caches, opening JARs by hand with jar tf, picking one by guesswork, and trying to answer a question your IDE would answer in one keystroke: does this superclass have a public utility method called X?

The Solution

jvmsrc queries your build tool (Gradle) for this project's resolved classpath, then hands your agent real source, real signatures, and real structure — for the exact version your build actually uses.

• As an MCP server – Connect to Claude Code, Cursor, Windsurf, or any other MCP host and equip your agent with six purpose-built classpath tools.
• As the jvmsrc CLI – Same engine, scriptable, pipe-friendly, and useful on its own when you just want to read a class.

What it saves, daily

On JVM projects with private libraries and no public Javadocs, jvmsrc is a force multiplier:

• ~50K tokens saved per "what's on this external class" investigation — roughly 70% reduction in cost.
• 15+ agent panic loops avoided daily — no grinding through Gradle caches, opening wrong JARs, or giving up.
• Unlock delegation for complex tasks touching internal SDKs that you previously had to do yourself.

The Difference in Action

Without jvmsrc (The 25-turn blind grind)

User: Override the audit hook from AbstractTradingService — is there a public utility method on it we should reuse?

Agent:

1. Searches workspace for AbstractTradingService.java ➔ 0 hits
2. Runs: find ~/.gradle -name "trading-core*"
3. Finds 4 versions: 2.1.0, 2.3.0, 2.4.1, 3.0.0-SNAPSHOT
4. Guesses: Picks trading-core-2.4.1.jar (the project actually uses 3.0.0-SNAPSHOT!)
5. Runs: jar tf and javap -p on the wrong JAR
6. [22 turns later] "I don't see a utility method, you'll have to implement it yourself."

Reality: 3.0.0-SNAPSHOT added maskSensitiveFields() as a protected helper exactly for this case. The agent didn't hallucinate — it was just blind.

With jvmsrc (The 3-turn instant resolution)

User: Override the audit hook from AbstractTradingService — is there a public utility method on it we should reuse?

Agent:

1. search_classes("AbstractTradingService") ➔ Finds FQN & exact resolved library.
2. get_class_structure(scope: "overview") ➔ Discovers maskSensitiveFields() in 3.0.0-SNAPSHOT.
3. get_method_signature("maskSensitiveFields") ➔ Gets accurate signature and generics.

Result: Writes the override correctly on the first try. No cache walking, no guessing, no wrong version.

How It Works

1. Build Tool Inquiry: jvmsrc queries your active build tool (e.g., Gradle) for the exact resolved classpath configuration.
2. Intelligent Caching: It caches the resolved classpath, tracking changes to build files to stay current.
3. Precision AI Tools: Instead of full-code dumping, it exposes precise, high-granularity tools (signatures, structure, search) to keep context windows small and token usage ultra-low.

Installation & Quick Start

1. Install CLI

npm install -g jvmsrc
# or use it directly via npx: npx jvmsrc <command>

[!IMPORTANT]
Requires Node ≥ 20 and Java on PATH (for CFR decompiler + javap).

2. Configure for your Workspace (MCP)

Generate a paste-ready MCP configuration for your project:

jvmsrc config --project /path/to/gradle-project

Paste this configuration into your AI assistant config (Claude Code, Cursor, Windsurf, etc.), restart the host, and you are ready to go!

MCP Server Reference

The MCP server runs over stdio via jvmsrc mcp. Add this to your host config:

{
  "mcpServers": {
    "jvmsrc": {
      "command": "jvmsrc",
      "args": ["mcp"]
    }
  }
}

Tools your agent gets

| Tool | What it does | |:---|:---| | search_classes | Find a class by simple name or glob; returns compact FQN + lib name lists | | get_class_structure | Retrieves class overview (purpose + method names) or declared signatures | | get_method_signature| Fetches real overloads for a method, with parameter names and generics | | find_in_class_source| Performs regex or substring searches inside a resolved class | | get_class_source | Retrieves method bodies or line ranges (used as a last resort) | | resolve_dependencies| Analyzes the actual dependency graph this project uses |

[!TIP]
Every source response includes sourceAvailable: true for real sources (Javadoc, parameter names, generics), false for CFR decompilation (structure reliable, names may be synthetic).

How It Compares

| Tool | Approach | Gap | | :--- | :--- | :--- | | Cache Indexers / ~/.gradle grep | Scan global caches | No per-project resolved version | | Static Parsers (e.g., build.gradle parser) | Parse declarations only | Misses transitive dependencies, BOMs, dynamic versions | | mcp-javadoc / path-only CFR | User supplies manual JAR paths | No automatic build/classpath resolution | | Gradle MCP (Tooling API) | Task/build focused | Not optimized for classpath-accurate FQN source lookup | | jvmsrc | Queries actual build tool & caches | Version-correct sources and signatures for agents |

Target Audience

Primarily Java + Spring Boot projects on Gradle. Other JVM languages (Kotlin, Scala) and Android work today on a best-effort basis and are on the roadmap as first-class targets — see ROADMAP.md.

If you're on Maven or Bazel, it's planned but not shipping yet. Star the repo or open an issue and I'll prioritize accordingly.

Detailed Reference

Runtime: Node.js ≥ 20, Java on PATH.

Project types: JVM codebases (Java, Kotlin, Scala, Groovy). jvmsrc calls the build tool, not your editor.

| Build system | Status | |---|---| | Gradle | Supported — multimodule included | | Maven, Bazel | Planned (SPEC.md) |

Point -p / projectRoot at the Gradle root (settings.gradle(.kts) or root build.gradle(.kts)). Uses ./gradlew when present, else gradle on PATH. Maven-only trees get an explicit unsupported error.

Early software; the supported path is narrow:

| Area | Today | |---|---| | Build tool | Gradle only | | Integration | Groovy init script (--init-script) — not a Gradle Portal plugin | | Classpaths | Standard JVM + Kotlin MPP jvm* configurations when Gradle exposes them | | Output | Java-shaped .java text (sources JAR, inter-project src, or CFR) |

Composite builds, Android-only layouts, and exotic configurations are not fully validated. See ROADMAP.md.

• No telemetry.
• Local only — caches and diagnostics stay on disk; never writes under your project root.
• Subprocesses via argv only (no shell interpolation) — see SECURITY.md.
• Optional JVMSRC_ALLOWED_ROOTS to lock down which projects jvmsrc may resolve.

jvmsrc com.example.MyClass -p /path/to/gradle-project          # shorthand for get
jvmsrc get com.example.MyClass -p /path/to/project -q > MyClass.java
jvmsrc resolve -p /path/to/project --force-refresh
jvmsrc config jdk-roots add /path/to/jdks                      # one-time JDK roots setup
jvmsrc doctor java -p /path/to/project                         # check JDK requirement + selection
jvmsrc diagnostics last                                         # latest failure message
jvmsrc mcp                                                     # run as MCP server

Useful flags: -p / --project, --module (:core:api), --configuration, --include-test, --force-refresh, --verbose (Gradle stderr only), --method, --start-line / --end-line.

Repo fixture for testing: test/fixtures/gradle-smoke — jvmsrc get com.smoke.Core -p test/fixtures/gradle-smoke --module :core.

• Resolution failures: Run jvmsrc diagnostics last (or jvmsrc diagnostics last 5)
• Custom JDK install roots: Add once with jvmsrc config jdk-roots add /path/to/jdks
• JDK mismatch debugging: Run jvmsrc doctor java -p /path/to/project
• After upgrading jvmsrc: Restart your MCP host
• Stale classpath: Run jvmsrc resolve --force-refresh

| Variable | Purpose | |---|---| | JVMSRC_JAVA_HOME | Force JDK home for Gradle/CFR child processes | | JVMSRC_CONFIG_DIR | Global jvmsrc config directory (absolute) | | JVMSRC_CACHE_ROOT | Cache root (absolute) | | JVMSRC_LOG_DIR | Diagnostic logs (absolute) | | JVMSRC_ALLOWED_ROOTS | Allowed projectRoot prefixes | | JVMSRC_MAX_SOURCE_OUTPUT_CHARS | Max source body size (default 524288) | | JVMSRC_GRADLE_TIMEOUT_MS | Gradle timeout | | JVMSRC_CFR_PATH | Custom CFR JAR |

Defaults follow env-paths conventions per OS. Full layout: SPEC.md §6.

When JVMSRC_JAVA_HOME is not set, jvmsrc auto-discovers local JDKs from common paths such as ~/.jdks (IntelliJ), ~/.gradle/jdks, SDKMan, jenv, asdf, and OS-specific system install directories, plus your global configured JDK roots from jvmsrc config jdk-roots ....

Finally, an MCP That Doesn't Make Me Decompile JARs

"This tool is a revelation for anyone tired of LLMs hallucinating non-existent Spring APIs. It actually reads bytecode, providing accurate class definitions and source lookups without the usual 'vibes-based' guesswork. The search_classes functionality is incredibly precise, and the thoughtful implementation of javap fallback and granular scope controls (overview/declared/effective) makes navigating complex JARs painless. It’s fast, honest when it can't find a class, and handles cache management perfectly. A must-have for any dev struggling with dependency hell — it’s like having a senior engineer who actually enjoys reading documentation." — Claude (AI Reviewer)

Project Documentation

| Document | Contents | |:---|:---| | SPEC.md | Schemas, contracts, CLI/MCP details | | CONTRIBUTING.md | Build, test, PR notes | | RELEASING.md | Branching, semver, npm releases | | CHANGELOG.md | Version history | | ROADMAP.md | Status and planned work | | SECURITY.md | Vulnerability reporting |

Building from Source

git clone https://github.com/Sintexer/jvm-source-lens.git
cd jvm-source-lens
bun install && bun run setup:cfr && bun run build
node dist/cli.js --version

Full contributor workflow: CONTRIBUTING.md.

I built jvmsrc because I kept running into the same wall: agents that are great at writing Java but blind to the actual classpath. If it saves you the same 25-turn grind it saved me, that's exactly why this exists. Found a bug, have an idea, or just want to say it helped? Open an issue or a PR — I read everything.

License

MIT — see LICENSE.