Prism

IntelliJ plugin that gives coding agents a token-budgeted view of the code they're actually working on. Aider's repomap, but IDE-native.

What it does · Benchmark · Install · Usage · Limitations

What it does

get_context_capsule(filePath, line, budget) returns a JSON capsule with the target method, its class skeleton, callees, callers, and relevant types. Sections are priority-ranked and greedy-fit to the token budget. Anything that doesn't fit goes into omitted with a reason.

The Tool Window shows what the agent received so you can see it too.

Benchmark

Ktor issue #5412 - ClosedByteChannelException in the zstd decoder. ~250k-LOC repo, bug in one 130-line file.

Two fresh Claude Code sessions, Sonnet 4.6. Messages tokens from /context after localization, before any edits:

	No-Prism	Prism
Messages at T1	30.4k	15.0k
Full-file reads	6	0
MCP calls	0	1
Found target method	yes	yes
Found test location	no	yes

The Prism session used one grep to locate the candidate line, called get_context_capsule once, and stopped. Reproduce: reproduce/.

Capsule size (jtokkit cl100k_base)

File	LOC	Budget	Capsule tokens	Naive tokens	Saved	Omitted
SampleService.java	124	2000	515	807	36%	—
SampleService.java	124	500	490	807	39%	callees
LargeService.java	1676	2000	203	13143	98%	skeleton
SampleKotlinService.kt	86	2000	552	781	29%	—
SampleKotlinService.kt	86	500	493	781	37%	callees

Naive baseline is the full source file. On large files the skeleton alone exceeds budget, so only the target method is returned regardless of budget.

Install

Download prism-*.zip from Releases or build from source: ./gradlew buildPlugin → build/distributions/prism-0.1.0.zip.

Install in IDEA 2025.2+: Settings → Plugins → gear → Install Plugin from Disk.

Requires the bundled MCP Server plugin (IDEA 2025.2+ ships it).

Usage

Once the JetBrains MCP server is connected in Claude Code, get_context_capsule is in the tool list. Pass projectPath explicitly if you have multiple IDE windows open.

{
  "projectPath": "/path/to/repo",
  "filePath": "/path/to/repo/src/Zstd.jvm.kt",
  "line": 67,
  "budget": 2000
}

Making the agent actually use it

The tool being available doesn't mean the agent will call it - by default agents reach for Read. You need to tell it to use Prism. Two options:

Per-task prompt - add one line to your task:

Use get_context_capsule before reading any production file.

Project CLAUDE.md. Put it there and the agent picks it up automatically in every session for that repo:

## Context
When investigating code in this repo, call `get_context_capsule` before
reading production files. Pass the file and line of the suspicious method.

Limitations

• JVM only (Java, Kotlin). Python/JS/Go/Rust/C++ are out of scope as UAST doesn't cover them.
• During IDE indexing callers unavailable, target + skeleton still work.

Future work

• Non-JVM backends via tree-sitter.
• PageRank-style ranking on the call graph (closer to how Aider does it).
• Capsule diff between two calls.

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License: MIT.