capsulectx

Capsule

Compact, source-linked context packs for coding agents.

MCP gives agents tools. Skills give agents procedures. Capsules give agents compact project context.

Large repositories make coding agents burn tokens rediscovering the same files, decisions, conventions, and setup details over and over. Capsule targets a 50–70% reduction in repeated repository-discovery context for large, multi-session agent work.

Install

No install required — run directly with npx (always gets the latest version):

npx capsulectx init

Or install globally with your package manager:

# npm
npm install -g capsulectx

# pnpm
pnpm add -g capsulectx

# yarn
yarn global add capsulectx

# bun
bun add -g capsulectx

Keep it up to date:

npm install -g capsulectx --prefer-online

Tip: npx is the easiest option — it always runs the latest published version with no manual update step.

Quickstart

npx capsulectx init

Capsule scans your repo, optionally enriches capsules with AI (using your installed Claude CLI, API keys, or a generated prompt for any browser-based AI), and creates:

.capsules/
  index.md
  architecture.md
  setup.md
  api.md
  data.md
  ui.md
  testing.md
  deployment.md

Each capsule is a Markdown file with source fingerprints in JSON frontmatter:

---json
{
  "name": "api",
  "sources": ["src/api/**"],
  "fingerprints": { "src/api/users.ts": "sha256:..." },
  "updated_at": "2026-06-20T14:00:00.000Z"
}
---

# API Capsule

## Purpose

Request handlers, routes, controllers, and service boundaries.

## Key Files

- `src/api/users.ts`: source file matched by this capsule.

## Decisions

- Record stable decisions here so future agents do not rediscover them.

Agents read .capsules/index.md, choose the relevant capsule, check staleness, then inspect only the source files that actually matter.

Commands

Command	What it does
capsule init	Scan repo, run AI enrichment (optional), write all capsules
capsule enrich	Re-run AI enrichment on existing capsules
capsule apply	Apply AI-generated JSON to capsule Conventions and Decisions
capsule write <name>	Refresh one capsule from source (preserves your edits)
capsule refresh <name>	Explicitly refresh one capsule
capsule refresh --all	Explicitly refresh all detected capsules
capsule get <name>	Print one capsule to stdout
capsule scan	Print detected source groups without writing
capsule stale [name]	Check which source files changed since last write
capsule estimate <name>	Show estimated token savings for one capsule
capsule stats	Show token savings across all capsules
capsule report [name]	Show reproducible source/capsule/stale token savings
capsule report --write	Write .capsules/report.md as a proof artifact
capsule check	CI-friendly freshness/config check; exits nonzero on stale or missing capsules
capsule --mcp	Start MCP server for native agent integration

MCP Server

Capsule ships an MCP server so Claude Code and other MCP-compatible agents can natively discover and consume capsules — no manual file reads needed.

Add to your project's .claude/settings.json:

{
  "mcpServers": {
    "capsule": {
      "command": "npx",
      "args": ["capsulectx", "--mcp"]
    }
  }
}

Or globally in ~/.claude/settings.json to enable for all projects.

Once configured, agents get these tools automatically:

Tool	What it does
capsule_list	List all capsules with freshness status
capsule_get	Read a capsule's compressed context; warns when stale but does not write
capsule_refresh	Explicitly refresh one capsule or all capsules
capsule_stale	Check which capsules have outdated sources
capsule_stats	Show token savings per capsule
capsule_report	Show machine-readable discovery-savings proof
capsule_check	CI-style stale/missing/config check
capsule_init	Generate capsules for the current repo

Capsules are also available as MCP resources at capsule:///index and capsule:///{name}.

Seeing the savings

$ capsule report architecture

Capsule: architecture

  capsule       status     source   capsule     stale   saved
  architecture  fresh       9,607       417         0     96%

Token counts use the cl100k_base tokenizer for accurate measurement.

For CI, run:

npx capsulectx check

It exits nonzero when capsules are stale, missing, or blocked by invalid config.

Agent Workflow

Add this to AGENTS.md, CLAUDE.md, Cursor rules, or your agent instructions:

Before working in this repo:

1. Read `.capsules/index.md` if it exists.
2. Read the capsule matching the task area.
3. Run `capsule stale <name>` when the CLI is available.
4. If stale, inspect changed source files before editing.
5. Update capsules when durable project knowledge changes.

Works with any agent that can read files — Claude Code, Codex, Cursor, Windsurf, Devin, custom MCP agents.

Custom Groups

Capsule detects standard layouts out of the box. For non-standard structure, add .capsules/config.json:

{
  "groups": [
    {
      "name": "workers",
      "description": "Background jobs, queues, and scheduled tasks.",
      "sources": ["src/workers/**", "src/jobs/**"]
    }
  ],
  "ignore": ["legacy/**"]
}

A groups entry with the same name as a default group overrides it. New names are appended. ignore patterns extend the default ignore list.

See docs/capsule-format.md for the public capsule file format.

Building the Demo

The animation in this README is a generated GIF — no screen-recording tools required.

npm run demo

Requires rsvg-convert (librsvg / librsvg2-tools) and ffmpeg. The script outputs docs/demo.gif from SVG frames rendered at 2× for retina. See scripts/build-demo.mjs.

Status

Capsule is early but functional. Current capabilities:

• Language-agnostic repo scanning with monorepo support (Turborepo, pnpm workspaces)
• Static analysis: framework detection, table/model extraction, route detection, env vars
• AI enrichment on init — launches your installed Claude CLI, calls Claude/OpenAI API, or generates a prompt for any browser-based AI (Claude.ai, ChatGPT, Cursor, Windsurf)
• Write-safe re-generation: human edits to Conventions and Decisions are preserved on refresh
• MCP server for native Claude Code / agent integration
• Real token counting (cl100k_base) with savings dashboard
• TypeScript API surface extraction
• Binary file filtering
• Stale detection and token savings estimation
• Reproducible report and CI-friendly check
• Custom group config via .capsules/config.json
• Auto-patches CLAUDE.md, AGENTS.md, .cursorrules, .windsurfrules with capsule instructions

Roadmap:

• smarter write that diffs source changes and suggests targeted updates
• before/after token reports for real agent sessions
• GitHub Action wrapper for capsule check

Install for Local Development

git clone https://github.com/dawitlabs/capsule.git
cd capsule
npm install
npm run build
node dist/cli.js init

License

MIT