@sveltekit-openapi/core

Auto-generate OpenAPI 3.1 documentation from your SvelteKit API routes. No decorators, no wrappers, no new APIs to learn — just point it at your existing code.

npx @sveltekit-openapi/core generate

Why?

SvelteKit deliberately chose not to enforce typed API responses. That's fine — but it means there's no built-in way to generate API docs.

Existing community tools require JSDoc annotations or are deprecated. This tool takes a different approach: it reads your existing code with TypeScript AST analysis and produces an OpenAPI 3.1 spec. No annotations, no comments, no runtime dependencies.

• Got Zod schemas? Full docs with validation rules, examples, and enums.
• Just TypeScript? Route paths, methods, params, status codes, and auth — all auto-detected.
• No types at all? Endpoints still documented, just marked as object.

Install

# npm
npm install -D @sveltekit-openapi/core

# Deno
deno add jsr:@sveltekit-openapi/core

Quick Start

CLI

# Generate from default location (src/routes)
npx sveltekit-openapi generate

# With options
npx sveltekit-openapi generate \
  --routes-dir src/routes \
  --schema-files "src/lib/schemas/*.ts" \
  --output openapi.json \
  --title "My API" \
  --api-version "1.0.0"

# Preview discovered routes without generating
npx sveltekit-openapi preview

# Serve with interactive API docs viewer
npx sveltekit-openapi serve --theme swagger --open

Vite Plugin

// vite.config.ts
import { sveltekit } from '@sveltejs/kit/vite';
import { sveltekitOpenApi } from '@sveltekit-openapi/core/vite';
import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [
    sveltekit(),
    sveltekitOpenApi({
      output: 'static/openapi.json',
      schemaFiles: ['src/lib/schemas/*.ts'],
      info: {
        title: 'My API',
        version: '1.0.0',
      },
    }),
  ],
});

The Vite plugin:

• Generates on dev server start
• Watches +server.ts and schema files for changes, regenerates with 300ms debounce
• Serves an interactive API docs viewer at /_openapi during development
• Serves the raw spec at /_openapi/spec.json

Programmatic

// Node / npm
import { generate } from '@sveltekit-openapi/core';

// Deno / JSR
import { generate } from 'jsr:@sveltekit-openapi/core';

const result = await generate({
  routesDir: 'src/routes',
  schemaFiles: ['src/lib/schemas/*.ts'],
  output: 'openapi.json',
});

console.log(`Generated ${result.endpointCount} endpoints from ${result.routeCount} routes`);
// result.document contains the full OpenAPI 3.1 object

How It Works

The tool uses a tiered inference model — it documents what it can infer and clearly marks what it can't.

Tier 1 — Automatic (zero effort)

Everything below is detected automatically from your +server.ts files via ts-morph AST analysis:

Tier 2 — Full Docs (you provide Zod schemas)

When you have Zod schemas, the tool extracts full type information by statically walking the Zod method chain (no runtime execution):

// src/lib/schemas/auth.ts
export const registerSchema = z.object({
  email: z.string().email().openapi({ example: '[email protected]' }),
  password: z.string().min(8).max(128),
  firstName: z.string().min(1).max(255),
}).openapi('RegisterRequest');

This produces a fully documented JSON Schema component:

{
  "RegisterRequest": {
    "type": "object",
    "properties": {
      "email": { "type": "string", "format": "email", "example": "[email protected]" },
      "password": { "type": "string", "minLength": 8, "maxLength": 128 },
      "firstName": { "type": "string", "minLength": 1, "maxLength": 255 }
    },
    "required": ["email", "password", "firstName"]
  }
}

Supported Zod features:

Schemas are registered as named components via .openapi('Name') and referenced with $ref in the output.

Tier 3 — Fallback

Endpoints without type information are still documented — request/response bodies are typed as object. You get the route, method, params, and status codes regardless.

Interactive API Docs Viewer

The serve command starts a local server with an interactive API documentation viewer. Three themes available, all loaded from CDN with zero extra dependencies:

npx sveltekit-openapi serve --theme swagger   # Classic Swagger UI (default)
npx sveltekit-openapi serve --theme scalar    # Modern Scalar API Reference
npx sveltekit-openapi serve --theme redoc     # Clean Redoc documentation

Options:

npx sveltekit-openapi serve \
  --theme swagger \        # swagger | scalar | redoc (default: swagger)
  --port 4242 \            # port to serve on (default: 4242)
  --open                   # auto-open browser

The viewer is also available in the Vite plugin at /_openapi during development, configured via the viewer option in your config.

The viewer renders the generated spec — it does not run your SvelteKit app. To test endpoints with "Try it", run your app separately.

Configuration

Create sveltekit-openapi.config.ts (or .js, .mjs) in your project root:

import type { SvelteKitOpenAPIConfig } from '@sveltekit-openapi/core';

export default {
  routesDir: 'src/routes',
  output: 'openapi.json',
  format: 'json', // or 'yaml'

  info: {
    title: 'My API',
    version: '1.0.0',
    description: 'My SvelteKit API',
  },

  servers: [
    { url: 'https://api.example.com', description: 'Production' },
    { url: 'http://localhost:5173', description: 'Development' },
  ],

  // Glob patterns for Zod schema files
  schemaFiles: ['src/lib/schemas/**/*.ts'],

  // Auth detection
  auth: {
    // Function names that indicate authentication
    patterns: ['requireAuth', 'requireRole'],
    // Custom security scheme (default: Bearer JWT)
    securityScheme: {
      type: 'http',
      scheme: 'bearer',
      bearerFormat: 'JWT',
    },
  },

  // Tag generation
  tags: {
    segmentIndex: 0, // Which path segment after /api/vN/ to use for tags
  },

  // Viewer theme for serve command and Vite plugin
  viewer: 'swagger', // 'swagger' | 'scalar' | 'redoc'

  // Glob patterns to exclude
  exclude: ['**/internal/**'],
} satisfies SvelteKitOpenAPIConfig;

CLI flags override config file values.

Output Example

Running against a real SvelteKit project (23 routes, 29 endpoints, 20 Zod schemas):

{
  "openapi": "3.1.0",
  "info": { "title": "My API", "version": "1.0.0" },
  "paths": {
    "/api/v1/auth/login": {
      "post": {
        "operationId": "postAuthLogin",
        "tags": ["auth"],
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "type": "object",
                "properties": {
                  "email": { "type": "string" },
                  "password": { "type": "string" }
                }
              }
            }
          }
        },
        "responses": {
          "200": { "description": "Success" },
          "400": {
            "description": "Bad Request",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": { "message": { "type": "string" } },
                  "required": ["message"]
                }
              }
            }
          },
          "401": { "description": "Unauthorized" },
          "403": { "description": "Forbidden" },
          "500": { "description": "Internal Server Error" }
        }
      }
    },
    "/api/v1/admin/users": {
      "get": {
        "operationId": "getAdminUsers",
        "tags": ["admin"],
        "parameters": [
          { "name": "search", "in": "query", "required": false, "schema": { "type": "string" } },
          { "name": "role", "in": "query", "required": false, "schema": { "type": "string" } }
        ],
        "responses": { "200": { "description": "Success" } },
        "security": [{ "bearerAuth": [] }],
        "summary": "Requires role: admin"
      }
    }
  },
  "components": {
    "schemas": {
      "RegisterRequest": {
        "type": "object",
        "properties": {
          "email": { "type": "string", "format": "email", "example": "[email protected]" },
          "password": { "type": "string", "minLength": 8, "maxLength": 128 },
          "firstName": { "type": "string", "minLength": 1, "maxLength": 255 }
        },
        "required": ["email", "password", "firstName"]
      }
    },
    "securitySchemes": {
      "bearerAuth": { "type": "http", "scheme": "bearer", "bearerFormat": "JWT" }
    }
  },
  "tags": [
    { "name": "admin" },
    { "name": "auth" },
    { "name": "courses" },
    { "name": "enrollments" }
  ]
}

Architecture

src/
├── index.ts              # Library entry: generate(config?)
├── cli.ts                # CLI: generate, preview, serve commands
├── vite.ts               # Vite plugin: sveltekitOpenApi()
├── viewer.ts             # HTML viewer: Swagger UI / Scalar / Redoc
├── types.ts              # Config + internal types (uses openapi3-ts)
├── core/
│   ├── scanner.ts        # Discovers +server.ts files, converts paths
│   ├── parser.ts         # Orchestrates per-file AST analysis
│   ├── schema-extractor.ts  # Zod chain → JSON Schema conversion
│   └── generator.ts      # Assembles final OpenAPI 3.1 document
└── analyzers/
    ├── auth.ts           # requireAuth / requireRole detection
    ├── route-params.ts   # event.params destructuring
    ├── query-params.ts   # searchParams.get() calls
    ├── request-body.ts   # request.json() + schema detection
    └── response.ts       # json() calls, status codes

Data flow:

Scanner (filesystem) → Parser (ts-morph AST) → Generator (OpenAPI 3.1)
                         ↑ uses 5 analyzers     ↑ uses schema registry
                         ↑                      ↑
                    Schema Extractor (Zod files) ─┘

What This Tool Does NOT Do

• It does not wrap your handlers. Your code stays exactly the same.
• It does not require Zod. Zod makes the output better, but it's optional.
• It does not execute your code. Everything is static analysis via the TypeScript AST.
• It does not generate client code. Use the OpenAPI spec with openapi-typescript or any codegen tool.
• It does not add runtime dependencies. It's a dev tool — zero impact on your bundle.

CLI Reference

Usage: sveltekit-openapi [command] [options]

Commands:
  generate [options]    Generate OpenAPI documentation (default)
  preview [options]     Preview discovered routes without generating
  serve [options]       Generate and serve API docs with interactive viewer

Generate options:
  -c, --config <path>          Path to config file
  -o, --output <path>          Output file path (default: "openapi.json")
  -f, --format <format>        Output format: json or yaml (default: "json")
  -r, --routes-dir <path>      Routes directory (default: "src/routes")
  -s, --schema-files <globs>   Glob patterns for schema files
  --title <title>              API title
  --api-version <version>      API version

Serve options:
  -c, --config <path>          Path to config file
  -p, --port <port>            Port to serve on (default: 4242)
  -t, --theme <theme>          Viewer: swagger, scalar, or redoc (default: "swagger")
  --open                       Open browser automatically
  (also accepts all generate options)

Examples

The examples/ directory contains four SvelteKit API projects you can run the tool against:

# Clone and try
git clone https://github.com/moo3/sveltekit-openapi.git
cd sveltekit-openapi
npm install && npm run build
node dist/cli.js serve -c examples/zod-heavy/sveltekit-openapi.config.ts --theme swagger --open

See examples/README.md for details on what each project demonstrates.

Dependencies

All viewer themes (Swagger UI, Scalar, Redoc) are loaded from CDN at runtime — no additional install.

License

MIT