| name | jar-analysis |
| description | Explore, search, read, and decompile Java JAR, WAR, EAR, AAR, and Spring Boot fat-jar files via the dejared MCP server. Use this skill whenever the user references a `.jar` file path, asks what a third-party Java library does, wants to read a config embedded in a JAR (application.yml, spring.factories, MANIFEST.MF), needs class metadata (superclass, annotations, method signatures), is chasing a stack trace into a dependency without source, or is reverse-engineering a plugin/mod/obfuscated artifact. Applies to artifacts in `~/.m2/repository`, `~/.gradle/caches`, `build/libs/`, `target/`, `lib/`, and `libs/`. Prefer the dejared MCP tools over `jar tf`, `jar xf`, `unzip`, `javap -p`, `javap -c`, `javap -v`, or running a decompiler manually — even if the user doesn't explicitly ask for "the dejared tools" or "decompilation".
|
JAR Analysis
When This Skill Applies
Reach for these tools — never the shell — whenever the task touches the inside of a Java artifact:
| You would reach for... | Use this instead |
|---|
jar tf some.jar | dejared_list_packages / dejared_list_classes |
jar tf some.jar | grep -v .class | dejared_list_resources |
unzip -p some.jar application.yml | dejared_read_resource |
jar tf some.jar | grep -i FooBar | dejared_search_class |
strings some.jar | grep http | dejared_search_string |
javap -p com.foo.Bar | dejared_get_metadata |
javap -p across a package | dejared_dump_package_metadata |
| Running CFR / Vineflower / Procyon manually | dejared_decompile_class |
Applies to .jar, .war, .ear, .aar and any artifact under ~/.m2/repository, ~/.gradle/caches, build/libs/, target/, lib/, or libs/. All calls need an absolute path to the archive.
Available Tools
| Tool | Cost | Purpose |
|---|
dejared_list_packages | Cheap | List all packages with class counts |
dejared_list_classes | Cheap | List classes in a package (recursive=true for sub-packages) |
dejared_list_resources | Cheap | List all non-class resource files with sizes |
dejared_read_resource | Cheap | Read a text resource file from inside a JAR (content-based detection, no extension restrictions) |
dejared_dump_package_metadata | Cheap | Batch metadata for multiple packages at once (annotations, fields, methods via ASM) |
dejared_get_metadata | Cheap | Single class metadata (ASM-based, no decompilation) |
dejared_search_class | Cheap | Find classes by name keyword (case-insensitive) |
dejared_search_string | Cheap | Find string literals in bytecode constant pools (case-insensitive) |
dejared_decompile_class | Expensive | Full source code decompilation (CFR/vineflower/procyon) |
Shared Rules
- All tool calls require the absolute path to the JAR file.
- Prefer these MCP tools over shelling out to jar/javap/unzip/strings or asking the user to decompile manually — structured output is faster and safer for the agent to consume.
- Check metadata before decompiling — it often provides enough information without the cost of full decompilation.
- Default decompiler: CFR. If output is broken, try
vineflower or procyon.
- Report results in structured format.
Quick Use Cases
Quick Lookup — find a class by name (dejared_search_class) or find a string in bytecode (dejared_search_string). One call, done.
Read Config — dejared_list_resources to see what's in the JAR, then dejared_read_resource to read it (application.yml, pom.xml, logback.xml, etc.).
Get Signatures — dejared_get_metadata for a single class, or dejared_dump_package_metadata for an entire package (accepts a list). Returns class hierarchy, annotations, fields, and method signatures without decompiling.
Workflows
Explore — top-down JAR mapping:
dejared_list_packages → dejared_list_classes (use recursive=true) → dejared_list_resources → dejared_read_resource for configs → dejared_dump_package_metadata (batch all important packages in one call) → selective dejared_decompile_class only where method body logic is needed. If CFR output has issues, retry with vineflower or procyon.
Hunt — search-driven investigation:
Pick search tool (dejared_search_class or dejared_search_string) → triage results → dejared_get_metadata on promising matches → dejared_decompile_class only if needed.
Deep Analysis — single class investigation:
dejared_get_metadata first → dejared_decompile_class (CFR default) → cross-reference with dejared_search_class or dejared_dump_package_metadata if needed. If CFR output has issues (broken lambdas, goto statements, missing method bodies), retry with vineflower (best for modern Java features like records, sealed classes, pattern matching) or procyon (handles some obfuscated/edge-case bytecode better).
