Open Responses Server
Open-source server bridging any OpenAI-compatible backend to the Responses API with MCP support.
A clever open-source bridge for unifying non-OpenAI backends under the Responses API. Its MCP and stateful features are standouts, but in-memory history and limited built-in security mean it's best for dev/experimental use, not production.
- Developers running Codex CLI with local models
- Teams standardizing on Responses API across backends
- Early adopters building MCP-powered agents
- Self-hosted LLM users needing stateful tool calls
- Non-technical users looking for a GUI chatbot
- Production deployments without rate limiting or persistence
- Teams needing built-in user authentication & multi-tenant support
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In short
Open Responses Server — Open-source server bridging any OpenAI-compatible backend to the Responses API with MCP support. Best for Developers running Codex CLI with local models, Teams standardizing on Responses API across backends, Early adopters building MCP-powered agents. Free to use.
Viability Score
How likely is Open Responses Server to still be operational in 12 months? Based on 4 signals — momentum (how recently it shipped), wrapper dependency, revenue model, and web presence.
Last calculated: July 2026
How we score →Key Features
- Drop-in OpenAI Responses API server for any backend
- MCP server integration for Chat Completions and Responses
- Stateful multi-turn conversation history (in-memory)
- Tool call execution loop with configurable iteration limits
- SSE event streaming for real-time responses
- CLI tool 'otc' for configuration, start, and management
- Ollama and vLLM compliance out of the box
- Extensible via plugins (web search, RAG)
- Environment variable or interactive configuration
- MIT licensed open-source
- Supports OpenAI Codex CLI and other Responses API clients
- Web search and RAG extension guide available
- Security scanning setup and policies included
- Testing guide with coverage instructions
- Publishing to PyPI workflow documented
About Open Responses Server
Open Responses Server is a plug-and-play, open-source server that translates any OpenAI-compatible API endpoint into OpenAI's Responses API interface. Designed to support Codex CLI and other Responses API clients, it adds stateful conversation management, tool execution loops, and MCP server integration on top of backends like Ollama, vLLM, LiteLLM, or Groq. The server handles multi-turn chat history in memory, orchestrates tool calls with configurable iteration limits, and emits SSE for streaming. Key features include a drop-in replacement for the Responses API, full MCP integration for both Chat Completions and Responses endpoints, and a CLI wizard (`otc`) for configuration and management. It is MIT-licensed and installable via PyPI (`pip install open-responses-server`). The documentation covers architecture, event sequences, testing, security scanning, and publishing workflows. Best suited for developers running local or self-hosted LLMs who need to standardize on the Responses API without vendor lock-in. It is not a production-ready platform but a developer tool for experimental and prototype workflows.
Behind the Verdict
Open Responses Server fills a specific niche: developers who want to use OpenAI's newer Responses API with local or third-party models. Its chief value is as a drop-in adapter—point it at any OpenAI-compatible endpoint, and it surfaces the Responses API. The MCP integration is a plus, allowing tools like Codex CLI to work with models they otherwise couldn't. Where it excels is in prototyping agentic workflows. The stateful conversation management and tool call execution loop save you from building that plumbing yourself. For a solo dev or small team experimenting with local LLMs, it's a time-saver. The `otc` CLI makes setup straightforward. But it's not production-ready. In-memory history means conversations vanish on restart. There's no built-in rate limiting, authentication, or multi-tenant support—you'd need to layer those on yourself. The project is young (v0.x), so expect rough edges and limited community support. Compared to alternatives like LiteLLM (which proxies multiple APIs to a unified format) or ollama's built-in API, Open Responses Server is more specialized—it targets the Responses API specifically, not a general proxy. LiteLLM gives you broader API coverage and more production features (load balancing, budget tracking), but lacks the MCP integration and stateful tool loop. We'd reach for this when hacking on a proof-of-concept with Codex CLI and local models, or when we need to test Responses API features without paying OpenAI. It's not for building customer-facing products. If you need persistence, auth, or scale, look elsewhere—or contribute to the project.
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Use Cases
- Run Codex CLI with a local Ollama model instead of OpenAI.
- Expose a vLLM endpoint as a stateful Responses API server.
- Build MCP-based agents that use any OpenAI-compatible backend.
- Prototype tool-calling workflows without leaving the Responses API spec.
- Standardize development on the Responses API across multiple backend providers.
Limitations
- Conversation history is stored only in-memory (no persistent database).
- No built-in rate limiting, user authentication, or multi-tenant support.
- Configuration is limited to a single backend URL and API key.
- Not suitable for high-load production without additional infrastructure.
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