@anthropic/slim-api

Express/Fastify middleware for automatic SLIM API response compression. Reduce API bandwidth by 40-50% with zero code changes.

Installation

``bash
npm install @anthropic/slim-api
`

Quick Start

$3

`typescript
import express from 'express';
import { slimMiddleware } from '@anthropic/slim-api/express';

const app = express();

// Add SLIM middleware
app.use(slimMiddleware());

// Your existing routes - no changes needed!
app.get('/api/users', (req, res) => {
res.json({ users: [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }] });
// If client sends Accept: application/slim
// Response is SLIM-encoded automatically
});

app.listen(3000);
`

$3

`typescript
import Fastify from 'fastify';
import { slimPlugin } from '@anthropic/slim-api/fastify';

const app = Fastify();

// Register SLIM plugin
app.register(slimPlugin);

// Your existing routes
app.get('/api/users', async () => {
return { users: [{ id: 1, name: 'Alice' }] };
});

app.listen({ port: 3000 });
`

$3

`typescript
import { SlimClient } from '@anthropic/slim-api/client';

const client = new SlimClient('https://api.example.com');

// Automatically requests SLIM, decodes response
const { data, isSlim, compressionRatio } = await client.get('/api/users');

console.log(data); // { users: [...] }
console.log(isSlim); // true
console.log(compressionRatio); // 42.5
`

How It Works

$3

`
Client Request:
Accept: application/slim, application/json

Server Response (if client accepts SLIM):
Content-Type: application/slim
X-Original-Size: 1250
X-Slim-Size: 780
X-Compression-Ratio: 37.6

{users:|2|id#,name,active?|1,Alice,T|2,Bob,F}

Server Response (fallback for non-SLIM clients):
Content-Type: application/json

{"users":[{"id":1,"name":"Alice","active":true},{"id":2,"name":"Bob","active":false}]}
`

Middleware Options

`typescript
app.use(slimMiddleware({
// Only SLIM responses larger than threshold (bytes)
threshold: 1024, // default: 0

// Skip certain paths
skip: (req) => req.path.startsWith('/static'),

// Force SLIM regardless of Accept header
force: false, // default: false

// Add compression stats headers
includeStats: true, // default: true

// Custom MIME type
mimeType: 'application/slim', // default
}));
`

Client Options

`typescript
const client = new SlimClient({
baseUrl: 'https://api.example.com',

// Fallback to JSON if SLIM fails
fallbackToJson: true, // default: true

// Request timeout (ms)
timeout: 5000, // default: 30000

// Custom headers
headers: { 'Authorization': 'Bearer ...' },

// Prefer JSON over SLIM
preferJson: false, // default: false
});
`

API Reference

$3

`typescript
import { slimMiddleware, slimBodyParser } from '@anthropic/slim-api/express';

// Response encoding
app.use(slimMiddleware(options));

// Request body parsing (for SLIM request bodies)
app.use(slimBodyParser());
`

$3

`typescript
import { slimPlugin } from '@anthropic/slim-api/fastify';

app.register(slimPlugin, options);
`

$3

`typescript
import { SlimClient, createSlimFetch, slimFetch } from '@anthropic/slim-api/client';

// Class-based client
const client = new SlimClient('https://api.example.com');
await client.get('/users');
await client.post('/users', { body: { name: 'Alice' } });
await client.put('/users/1', { body: { name: 'Updated' } });
await client.patch('/users/1', { body: { active: false } });
await client.delete('/users/1');

// Factory function
const fetch = createSlimFetch({ baseUrl: 'https://api.example.com' });
await fetch('/users');

// Standalone function
import { slimFetch } from '@anthropic/slim-api/client';
await slimFetch('https://api.example.com/users');
`

Response Object

`typescript
interface SlimResponse {
data: T; // Decoded response data
headers: Headers; // Response headers
status: number; // HTTP status code
isSlim: boolean; // Was response SLIM-encoded?
originalSize?: number; // Original JSON size (bytes)
slimSize?: number; // SLIM size (bytes)
compressionRatio?: number; // Compression percentage
}
`

Benchmarks

| Response Type | JSON Size | SLIM Size | Savings |
|---------------|-----------|-----------|---------|
| User list (10) | 2.5 KB | 1.5 KB | 40% |
| Product catalog | 15 KB | 8 KB | 47% |
| Dashboard data | 50 KB | 28 KB | 44% |
| Paginated list | 100 KB | 55 KB | 45% |

Use Cases

- Mobile APIs: Reduce bandwidth for mobile apps
- Real-time dashboards: Faster data updates
- Microservices: Internal service communication
- Public APIs: Optional SLIM support for bandwidth-conscious clients
- AI/LLM APIs: Reduce token usage when passing API data to LLMs

Browser Support

The client works in all modern browsers that support fetch`. For older browsers, use a fetch polyfill.

License

MIT