Auto-Diagram: Zero-Config Codebase Visualization

Analyze ANY codebase and generate a complete architecture diagram automatically. No description needed — you read the code and figure out what to draw.

Prerequisite Check

Before starting analysis, verify the Excalidraw MCP server is available:

mcp__excalidraw__read_diagram_guide()

If this fails, tell the user:

"The Excalidraw MCP server isn't running. Start the canvas server first: npx excalidraw-toolkit start The default port is 3000. To use a different port, re-init and start with the same port: PORT=3001 npx excalidraw-toolkit init && PORT=3001 npx excalidraw-toolkit start Then open http://localhost:3000 (or your configured port) and try again."

Context Budget

To prevent context window blowout on large codebases, follow these hard limits:

Operation	Limit
Grep results per pattern	20 matches (use head_limit)
Files read per component	5 files
Tool calls in Phase 2	15
Tool calls in Phase 3	10

If limits are exceeded, proceed with partial results and note gaps to the user.

Analysis Pipeline

Phase 1: Project Detection

Run these file checks to identify the project type and tech stack:

Read root files -- check for package.json, pyproject.toml, go.mod, Cargo.toml, pom.xml, Gemfile, composer.json, mix.exs, Makefile, Dockerfile, docker-compose.yml, *.tf
Scan directory structure -- ls the root and first-level subdirectories to identify the layout pattern
Detect project type:
- Monorepo: workspaces in package.json, lerna.json, pnpm-workspace.yaml, multiple go.mod files, packages/ or apps/ directories
- Microservices: Multiple Dockerfile files, docker-compose.yml with 3+ services
- Standard app: Single service with standard directory structure
Check for frameworks -- look for markers:
- React/Next.js: next.config.*, src/app/, src/pages/
- Express/Fastify/Hono: routes/, controllers/, middleware/
- Nest.js: @nestjs/core in package.json
- Django/Flask/FastAPI: manage.py, wsgi.py, app.py, main.py with uvicorn
- Spring: src/main/java/, application.properties
- Go services: cmd/, internal/, pkg/
- Rust: src/main.rs, src/lib.rs
- Rails: Gemfile + config/routes.rb
- Laravel: artisan, app/Http/
- Phoenix/Elixir: mix.exs + lib/*_web/

Output: A mental model of the project type, primary language, and framework.

Monorepo handling: If monorepo detected, scope analysis to the top-level package structure first. Show one box per package/app. Offer to drill into specific packages on request.

Phase 2: Component Discovery

Based on project type, identify architectural components. Max 15 tool calls.

For Web Applications:

Frontend -- Glob *.tsx, *.jsx, *.vue, *.svelte in src/, app/, pages/ (head_limit: 20)
API routes -- Grep route definitions: router\.(get|post|put|delete), @(Get|Post|Put|Delete), @app\.route, HandleFunc (head_limit: 20)
Database -- Look for prisma/schema.prisma, models.py, *.entity.ts, migrations/, @Entity, db.Model (head_limit: 20)
External services -- Grep for SDK/HTTP client imports: axios, fetch(, requests\., http\.NewRequest (head_limit: 20)
Message queues -- Grep: amqp, kafka, bull, celery, SQS, pubsub (head_limit: 10)
Cache -- Grep: redis, memcached, cache in imports (head_limit: 10)
Auth -- Grep: passport, jwt, oauth, @Auth, middleware.*auth (head_limit: 10)

For Infrastructure:

Services -- Read docker-compose.yml service definitions
Cloud resources -- Grep *.tf for resource " blocks (head_limit: 20)
K8s -- Glob **/k8s/*.yaml or **/manifests/*.yaml (head_limit: 20)

For Libraries/CLIs:

Entry points -- Find main, bin, exports in package config
Modules -- Map public API surface (read index/main files)
Dependencies -- Read dependency list from package config

Output: A list of 4-12 components with names, types, and key file locations.

Phase 3: Connection Mapping

Determine how components connect. Max 10 tool calls. Focus on entry points and their immediate dependencies -- don't trace every import.

Read entry point files -- For each major component, read the main/index file (max 5 files total). Look for:
- Import statements that reference OTHER components (not third-party packages)
- Function calls to other services (HTTP clients, RPC calls, queue publishers)
- Database connection/query code
- Event emitters/listeners
Map connection types -- Categorize each connection:
- REST/HTTP -- fetch/axios/requests calls
- SQL/ORM -- database queries
- gRPC/RPC -- inter-service calls
- Event/Queue -- pub/sub, message queues
- Import -- direct module import (same codebase)
Build edge list -- Directed edges: ComponentA --[protocol]--> ComponentB

If you can't determine connections reliably: Show components without arrows and note "connections could not be auto-detected from entry point analysis. Try: 'add connections between X and Y'."

Output: A list of directed edges with labels.

Phase 4: Verify with User

Before drawing, present a summary and ask for confirmation:

"I found N components and M connections in this codebase:

Components: [list with types] Connections: [list of edges]

Does this look right? Should I add, remove, or rename anything before generating the diagram?"

Wait for confirmation before proceeding. Incorporate any changes the user suggests.

Phase 5: Layout Selection

Choose layout based on the architecture pattern detected:

Pattern	Layout	Trigger
Request/response flow (most web apps)	Vertical flow (top→bottom)	Frontend + API + DB layers detected
Data pipeline / ETL	Horizontal pipeline (left→right)	Linear chain of transforms detected
Event-driven / microservices	Hub and spoke	Message broker/event bus detected
Monolith with modules	Vertical flow with zones	Single service, multiple internal modules

Tiebreaking: Prefer the pattern with more detected components. Default to vertical flow.

Hybrid: If both request/response and event-driven patterns exist, use vertical flow with the event bus in the middle layer (not hub-and-spoke).

Phase 6: Diagram Generation

Follow the excalidraw skill's workflow:

mcp__excalidraw__clear_canvas() -- start fresh
mcp__excalidraw__get_canvas_screenshot() -- verify empty
Plan coordinates using the sizing rules from the excalidraw skill
mcp__excalidraw__batch_create_elements(elements=[...]) -- all elements in ONE call
mcp__excalidraw__set_viewport({ scrollToContent: true }) -- zoom to fit
mcp__excalidraw__get_canvas_screenshot() -- verify result
Verify and fix -- check for overlapping labels, hidden arrows, cramped spacing. Fix with update_element or delete_element + create_element. Max 2 rounds.
Offer export and next steps

Color by component role:

Role	Background	Stroke
Frontend	`#a5d8ff`	`#1971c2`
Backend/API	`#d0bfff`	`#7048e8`
Database	`#b2f2bb`	`#2f9e44`
External service	`#ffc9c9`	`#e03131`
Queue/Event	`#fff3bf`	`#fab005`
Cache	`#ffe8cc`	`#fd7e14`

Label format: Each box should contain:

ComponentName
tech-stack
(key detail)

Example:

API Server
Express.js
/api/* routes

Grouping Heuristic (>12 components)

When more than 12 components are discovered:

Group by top-level directory first (e.g., all files under services/auth/ → "Auth Service")
If a directory contains >3 components, collapse into one zone named after the directory
Show the zone as a dashed rectangle containing a single summary box
Offer drill-down: "Want me to expand the [zone name] zone into its internal components?"

Constraints

Max 12 components per diagram. If more found, apply grouping heuristic above.
Max 20 arrows per diagram. Show primary data flow paths only. Use dashed lines for secondary connections.
Always include a title with the project name and "Architecture Overview"
Always include a legend if using more than 3 colors

Edge Cases

Situation	How to Handle
Empty or trivial repo (<5 files)	Generate a simple module diagram showing file relationships
Monorepo with many packages	Show package-level view first, offer drill-down per package
No clear architecture (scripts, notebooks)	Show file dependency graph instead
Can't detect connections	Show components without arrows, note it to user
User specifies a subdirectory	Scope analysis to that directory only
MCP server not running	Print setup instructions (see Prerequisite Check)
Context budget exceeded	Proceed with partial results, tell user what was skipped

Example: What Auto-Diagram Produces for a Next.js + Prisma App

User verification prompt:

I found 6 components and 5 connections in this codebase:

Components:

Next.js Frontend (pages/, components/) — Frontend

API Routes (pages/api/) — Backend/API

Prisma ORM (prisma/schema.prisma) — Database

PostgreSQL (from DATABASE_URL in .env.example) — Database

NextAuth (from imports in [...nextauth].ts) — Auth

Stripe API (from stripe SDK imports) — External API

Connections:

Frontend → API Routes (REST API)

API Routes → Prisma ORM (Prisma queries)

Prisma ORM → PostgreSQL (SQL)

API Routes → NextAuth (auth middleware)

API Routes → Stripe API (payment calls)

Does this look right?

Diagram layout: Vertical flow, 3 layers

┌─────────────────────────────────────────────┐
│  Frontend Layer                              │
│  ┌──────────────┐  ┌──────────────┐         │
│  │ Next.js App  │  │ React        │         │
│  │ pages/       │  │ components/  │         │
│  └──────┬───────┘  └──────────────┘         │
└─────────┼───────────────────────────────────┘
          │ API calls
┌─────────┼───────────────────────────────────┐
│  API Layer                                   │
│  ┌──────▼───────┐  ┌──────────────┐         │
│  │ API Routes   │  │ NextAuth     │         │
│  │ pages/api/   │──│ OAuth flow   │         │
│  └──────┬───────┘  └──────────────┘         │
└─────────┼───────────────────────────────────┘
          │ Prisma queries
┌─────────┼───────────────────────────────────┐
│  Data Layer                                  │
│  ┌──────▼───────┐  ┌──────────────┐         │
│  │ PostgreSQL   │  │ Stripe API   │         │
│  │ via Prisma   │  │ payments     │         │
│  └──────────────┘  └──────────────┘         │
└─────────────────────────────────────────────┘

After Diagram Delivery

Show this message once per conversation — only after the first successful diagram the user confirms they're happy with. Do not repeat on subsequent diagrams in the same session.

If you found this useful, I'd love your feedback! Feature requests, bug reports, or just a star: https://github.com/edwingao28/excalidraw-toolkit/issues/13

auto-diagram