🌉 LLM Bridge

The Universal Translation Layer for Large Language Model APIs

LLM Bridge is a powerful TypeScript library that provides seamless translation between different LLM provider APIs (OpenAI Chat Completions, OpenAI Responses API, Anthropic Claude, Google Gemini) while preserving zero data loss and enabling perfect reconstruction of original requests.

🚀 Why LLM Bridge Exists

The Problem

When building Infinite Chat API, we needed a way to create a proxy that supports multiple LLM providers. However, this is a difficult challenge, as I wrote in this blog post: The API layer for using intelligence is completely broken..

The particular challenges are in:

• Manipulating and creating proxies for different LLM providers
• Multi-modality
• Tool call chains
• Error handling

The Solution

LLM Bridge provides a universal format that acts as a common language between all major LLM providers, enabling:

✅ Perfect Translation - Convert between OpenAI, Anthropic, Google, and OpenAI Responses API formats
✅ Zero Data Loss - Every field is preserved with _original reconstruction
✅ Streaming Support - Parse and emit SSE streams across all providers
✅ Extended Thinking - Anthropic thinking blocks, Google thought parts, OpenAI reasoning
✅ Structured Output - JSON schema response formats across all providers
✅ Multimodal Support - Images, documents, and rich content across providers
✅ Tool Calling - Function calling translation between different formats
✅ Error Handling - Unified error types with provider-specific translation
✅ Type Safety - Full TypeScript support with strict typing

📦 Installation

npm install llm-bridge

🔧 Quick Start

Basic Usage

import { toUniversal, fromUniversal, translateBetweenProviders } from 'llm-bridge'

// Convert OpenAI request to universal format
const openaiRequest = {
  model: "gpt-4o",
  messages: [
    { role: "system", content: "You are a helpful assistant" },
    { role: "user", content: "Hello!" }
  ],
  temperature: 0.7,
  max_tokens: 1000
}

const universal = toUniversal("openai", openaiRequest)
console.log(universal.provider) // "openai"
console.log(universal.model)    // "gpt-4o"
console.log(universal.system)   // "You are a helpful assistant"

// Convert universal format back to any provider
const anthropicRequest = fromUniversal("anthropic", universal)
const googleRequest = fromUniversal("google", universal)

// Or translate directly between providers
const anthropicRequest2 = translateBetweenProviders("openai", "anthropic", openaiRequest)

OpenAI Responses API

// Convert OpenAI Responses API format
const responsesRequest = {
  model: "gpt-4o",
  input: [
    { role: "user", content: "What is the weather?" }
  ],
  tools: [
    { type: "function", name: "get_weather", parameters: { type: "object", properties: { location: { type: "string" } } } }
  ],
  max_output_tokens: 1000
}

const universal = toUniversal("openai-responses", responsesRequest)
const anthropicRequest = fromUniversal("anthropic", universal)

Streaming

import { parseOpenAIStream, emitAnthropicStream } from 'llm-bridge'

// Parse an OpenAI SSE stream into universal events
const universalEvents = parseOpenAIStream(openaiSSEStream)

// Re-emit as Anthropic SSE format
const anthropicStream = emitAnthropicStream(universalEvents)

// Or use the handler for full stream translation
import { handleUniversalStreamRequest } from 'llm-bridge'

const outputStream = handleUniversalStreamRequest(
  inputStream,
  "openai",    // source provider
  "anthropic", // target provider
  async (event) => event // optional transform
)

Extended Thinking

// Anthropic extended thinking
const anthropicRequest = {
  model: "claude-sonnet-4-20250514",
  max_tokens: 16000,
  thinking: { type: "enabled", budget_tokens: 10000 },
  messages: [{ role: "user", content: "Solve this complex problem..." }]
}

const universal = toUniversal("anthropic", anthropicRequest)
console.log(universal.thinking) // { enabled: true, budget_tokens: 10000 }

// Convert to Google format with thinking
const googleRequest = fromUniversal("google", universal)
// Includes thinkingConfig: { thinkingBudget: 10000 }

Structured Output

// OpenAI structured output
const openaiRequest = {
  model: "gpt-4o",
  messages: [{ role: "user", content: "Extract the name and age" }],
  response_format: {
    type: "json_schema",
    json_schema: {
      name: "person",
      schema: { type: "object", properties: { name: { type: "string" }, age: { type: "number" } } }
    }
  }
}

const universal = toUniversal("openai", openaiRequest)
// universal.structured_output contains the normalized schema

// Convert to Google format
const googleRequest = fromUniversal("google", universal)
// Includes generationConfig: { responseMimeType: "application/json", responseSchema: {...} }

Perfect Reconstruction

// Round-trip conversion with zero data loss
const original = { /* your OpenAI request */ }
const universal = toUniversal("openai", original)
const reconstructed = fromUniversal("openai", universal)

console.log(reconstructed === original) // Perfect equality!

🎯 Core Features

1. Universal Format Translation

LLM Bridge converts between provider-specific formats through a universal intermediate format:

OpenAI Chat ←→ Universal ←→ Anthropic
     ↕                        ↕
OpenAI Responses ←→ Universal ←→ Google

2. Supported Providers

Provider	Format	Features
OpenAI Chat Completions	openai	Messages, tools, developer role, reasoning_effort, structured output
OpenAI Responses API	openai-responses	Input items, reasoning config, built-in tools (web_search, file_search)
Anthropic Claude	anthropic	Messages, tools, extended thinking, cache_control, URL images
Google Gemini	google	Contents, function declarations, thinkingConfig, structured output

3. Streaming Support

Parse and emit Server-Sent Events (SSE) streams for all providers:

• Parsers: Convert provider SSE streams → universal stream events
• Emitters: Convert universal stream events → provider SSE streams
• Handler: Full stream translation pipeline with optional transforms

4. Multimodal Content Support

Handle images and documents seamlessly across providers:

// OpenAI format with image
const openaiMultimodal = {
  model: "gpt-4o",
  messages: [{
    role: "user",
    content: [
      { type: "text", text: "What's in this image?" },
      { type: "image_url", image_url: { url: "data:image/jpeg;base64,..." } }
    ]
  }]
}

// Translate to Anthropic (base64 source) or Google (inlineData)
const anthropicRequest = translateBetweenProviders("openai", "anthropic", openaiMultimodal)
const googleRequest = translateBetweenProviders("openai", "google", openaiMultimodal)

5. Function/Tool Calling Translation

Seamlessly translate tool calls between different provider formats:

const openaiWithTools = {
  model: "gpt-4o",
  messages: [
    {
      role: "assistant",
      tool_calls: [{
        id: "call_123",
        type: "function",
        function: { name: "get_weather", arguments: '{"location": "SF"}' }
      }]
    },
    {
      role: "tool",
      content: '{"temperature": 72}',
      tool_call_id: "call_123"
    }
  ],
  tools: [{
    type: "function",
    function: {
      name: "get_weather",
      description: "Get weather info",
      parameters: { type: "object", properties: { location: { type: "string" } } }
    }
  }]
}

// Translate to Google Gemini (functionCall/functionResponse)
const geminiRequest = translateBetweenProviders("openai", "google", openaiWithTools)

// Translate to Anthropic (tool_use/tool_result blocks)
const anthropicRequest = translateBetweenProviders("openai", "anthropic", openaiWithTools)

6. Error Handling & Translation

Unified error handling with provider-specific error translation:

import { buildUniversalError, translateError } from 'llm-bridge'

const error = buildUniversalError("rate_limit_error", "Rate limit exceeded", "openai", { retryAfter: 60 })

const anthropicError = translateError(error.universal, "anthropic")
const googleError = translateError(error.universal, "google")

7. Provider Detection

Automatically detect which provider format you're working with:

import { detectProvider } from 'llm-bridge'

detectProvider("https://api.openai.com/v1/chat/completions", body)  // "openai"
detectProvider("https://api.anthropic.com/v1/messages", body)       // "anthropic"
detectProvider("https://generativelanguage.googleapis.com/...", body) // "google"
detectProvider("https://api.openai.com/v1/responses", body)         // "openai-responses"

🔌 API Reference

Core Functions

• toUniversal(provider, body) - Convert provider format to universal
• fromUniversal(provider, universal) - Convert universal to provider format
• translateBetweenProviders(from, to, body) - Direct provider-to-provider translation
• detectProvider(url, body) - Auto-detect provider from URL and request format

Streaming Functions

• parseOpenAIStream(stream) - Parse OpenAI Chat Completions SSE stream
• parseAnthropicStream(stream) - Parse Anthropic Messages SSE stream
• parseGoogleStream(stream) - Parse Google Gemini SSE stream
• parseOpenAIResponsesStream(stream) - Parse OpenAI Responses API SSE stream
• emitOpenAIStream(events) - Emit OpenAI SSE format
• emitAnthropicStream(events) - Emit Anthropic SSE format
• emitGoogleStream(events) - Emit Google SSE format
• handleUniversalStreamRequest(stream, source, target, transform?) - Full stream translation pipeline

Utility Functions

• getModelDetails(model) - Get model information and capabilities
• getModelCosts(model) - Get pricing information for model
• countUniversalTokens(universal) - Estimate token usage
• createObservabilityData(universal) - Generate telemetry data

Error Handling

• buildUniversalError(type, message, provider, options) - Create universal error
• translateError(error, targetProvider) - Translate error between providers
• parseProviderError(error, provider) - Parse provider-specific errors

🧪 Testing

Run the comprehensive test suite:

npm test

Our test suite includes:

• ✅ 355+ passing tests
• ✅ Provider format conversion (OpenAI, Anthropic, Google, OpenAI Responses)
• ✅ Cross-provider round-trip translation
• ✅ Streaming parser and emitter tests
• ✅ Extended thinking and structured output
• ✅ Multimodal content handling
• ✅ Tool calling lifecycle across all providers
• ✅ Error handling and validation
• ✅ Edge cases and malformed input
• ✅ Type safety verification

📄 License

MIT License - see LICENSE file for details.

🙋‍♂️ Support

• 📖 Documentation
• 🐛 Report Issues
• 💬 Discussions

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Made with ❤️ by team supermemory