jskim

Token-saving Java file reader for AI coding agents, optimized for Spring Boot. Summarizes Java files compactly using tree-sitter, saving 70-80% of input tokens compared to reading files directly. Zero setup, no index: every run parses the current working tree.

A human counted the tokens. An AI counted the getters. Both decided life's too short.

Installation

pip install jskim

Requires Python 3.10+.

Usage

jskim auto-detects the mode based on whether you pass a file or directory.

Summarize a Java file

jskim <file.java>
jskim <file.java> --grep <pattern>        # filter methods by name/signature
jskim <file.java> --annotation <@Ann>     # filter methods by annotation
jskim A.java B.java C.java                # multiple files

Java simple source files without an explicit type wrapper are summarized as implicit class <FileStem>. A package-info.java shows its package-level annotations (Spring Modulith @ApplicationModule).

The summary shows the class Javadoc's first sentence, instance fields and static constants separately (non-private short string constants with their value), collapses dependency-injection constructors to one line, keeps annotation arguments that change behaviour (@RequiresPermission("trip.create"), @Transactional(readOnly = true)), drops OpenAPI/Swagger documentation annotations, renders nested types with their members, and resolves mapping paths from class constants (@PostMapping(path = ONE_TRIP + "/start") → @PostMapping("/trips/{tripId}/start")). Method line ranges start at the signature, not at the annotation block above it.

Project map

Generates a compact map of all Java files in a directory: packages (relative to the common root, with package-info.java annotations), classes, annotations, field/method counts, Lombok usage, enum constants, records by name. Build output directories (target/, build/) are skipped.

jskim <src_dir>
jskim <src_dir> --deps                 # package-to-package dependencies
jskim <src_dir> --endpoints             # REST endpoint map
jskim <src_dir> --beans                 # Spring bean DI graph + @Bean producers + config properties
jskim <src_dir> --callers Class.method  # upstream callers for a specific method
jskim <src_dir> --impact Class.method   # callers + direct callees for a specific method
jskim <src_dir> --impact Class.method --depth 2  # bounded hierarchy depth
jskim <src_dir> --package <text>        # filter by package (substring)
jskim <src_dir> --annotation <@Ann>     # filter by class annotation
jskim <src_dir> --extends <ClassName>   # filter by superclass
jskim <src_dir> --implements <Name>     # filter by implemented interface

Spring Boot flags:

• --endpoints — lists all REST endpoints: HTTP method, full path (base + method), handler, line number, and the handler's guard annotations with constants resolved (@RequiresPermission("trip.create")). Paths built from constants (@RequestMapping(BASE_PATH), TRIPS + "/{id}", ApiPaths.ROOT) are resolved across the project
• --beans — shows bean DI wiring (constructor parameters, or Lombok constructor + final fields, or @Autowired/@Inject fields), @Bean factory method producers (nested @Configuration classes included), and @ConfigurationProperties with prefix + field details
• --callers Class.method — shows resolved upstream callers for a specific method; use a fully-qualified class name when class names collide
• --impact Class.method — shows both upstream callers and downstream calls from the target method
• --depth N — controls caller/impact traversal depth; defaults to 1 to keep output compact
• --implements — filter classes by implemented interface name
• --deps — one block per package listing the other project packages it imports, extends or implements, and the types involved. Same-package references are omitted, so the output is the module-boundary view

Call hierarchy mode resolves same-class calls, static calls on project classes, and field calls such as billingService.create() when the field type points to a project class. A call through an interface or superclass also counts for every project implementation, so --callers AuditEventService.write finds the callers of AuditApi.write. It intentionally skips unresolved local-variable/parameter calls and ambiguous overload edges rather than guessing. Classes are shown by simple name and fully qualified only when the simple name is ambiguous.

Example:

jskim src/ --callers BillingService.create --depth 2

// === Callers: BillingService.create (depth 2) ===
// target: BillingService.create(BillDTO)  src/.../BillingService.java:L45
//
// callers:
//   ← BillingController.createBill(BillDTO)  src/.../BillingController.java:L62
//     ← BillingJob.retryFailedBills()  src/.../BillingJob.java:L30

jskim src/ --impact BillingService.create

// === Impact: BillingService.create (depth 1) ===
// target: BillingService.create(BillDTO)  src/.../BillingService.java:L45
//
// callers:
//   ← BillingController.createBill(BillDTO)  src/.../BillingController.java:L62
//
// calls:
//   → BillingRepository.save(Bill)  src/.../BillingRepository.java:L20
//   → BillingService.validate(BillDTO)  src/.../BillingService.java:L80

Diff mode

Summarizes only the Java files and methods changed in a git diff. Ideal for PR reviews.

jskim --diff HEAD~1                    # changes since last commit
jskim --diff main                      # changes vs main branch
jskim --diff main...feature-branch     # merge-base comparison
jskim src/ --diff HEAD~1               # scoped to directory
git diff main | jskim --diff -         # read diff from stdin

Output marks methods as [NEW], [MODIFIED], or [DELETED], and added/removed instance fields or record components as [FIELDS] +Type name, -Type name, nested types included. Getters/setters/boilerplate and dependency-injection constructor changes are suppressed. Deleted methods are shown with their previous signature when a base ref is available, so overload removals stay distinguishable.

Extract methods

jskim <file.java> --list                          # list all methods
jskim <file.java> <method_name>                    # extract one method
jskim <file.java> <method1> <method2> <method3>    # extract multiple

The extracted source keeps the Javadoc and behaviour annotations above the method and skips documentation-only annotations (@Operation, @ApiResponse, @Schema).

Method calls (→)

Each method in the skim output shows its direct method invocations:

// methods:
//     L45-L62 ( 18 lines): @PostMapping("/bills") public Bill createBill(@RequestBody BillDTO dto)
//                → auditLogger.log, billingService.create, notifyStakeholders, validator.validate
//     L64-L80 ( 17 lines): @GetMapping("/bills/{id}") public Bill getBill(@PathVariable Long id)
//                → billingService.findById

Every → entry can be followed: an unqualified name is a method in the same class, field.method resolves through the fields: section (billingService → BillingService, so skim BillingService.java next), and Class.method is a static call on a project class. Calls on local variables and parameters, JDK/Spring/library classes (Collectors.groupingBy, OffsetDateTime.now), static-imported members, ALL_CAPS constants, chained/fluent calls, logging, and collection plumbing are excluded because they cannot be followed from a summary.

Usage in Skill-enabled Agents

Any coding agent that can run shell commands can use jskim directly. The repo also includes a SKILL.md definition for environments that support skill-style tool packaging and auto-triggering.

One published install path for skill-enabled environments is the Vercel Skills Registry:

npx skills add garvit-joshi/jskim

In hosts that expose the skill as a slash command, invoke it with /jskim:

/jskim <file.java>              # summarize a file
/jskim <src_dir>                # project map
/jskim <file.java> <method>     # extract a method

Workflow

1. Explore — jskim src/ to understand project structure
2. Narrow — jskim src/ --package com.example.billing to focus on a package
3. Spring context — jskim src/ --endpoints --beans to see REST API + DI wiring
4. Understand — jskim File.java to see class structure, fields, methods, and calls
5. Trace — Follow → calls by matching field types to find the next class to skim
6. Impact — jskim src/ --callers Class.method or --impact Class.method to see resolved upstream/downstream method edges
7. Filter — jskim File.java --grep billing for large classes
8. Focus — jskim File.java methodA methodB to read specific methods
9. Edit — Read only the specific lines you need from the source file before editing

Dependencies

• tree-sitter — Incremental parsing library
• tree-sitter-java — Java grammar for tree-sitter