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Show HN: ChunkBack – A Fake LLM API server for testing apps without paying

forthwall Wednesday, November 19, 2025

Hi HN,

I've been working with LLMs in production for a while both as a solo dev building apps for clients and working at an AI startup. The one thing that always was a pain was to pay OpenAI/Gemini/Anthropic a few dollars a month just for me to say "test" or have a CI runner validate some UI code. So I built this server called ChunkBack, that mocks the popular llm provider's functionality but allows you to type in a deterministic language:

`SAY "cheese"` or `TOOLCALL "tool_name" {} "tool response"`

I've had to work in some test environments and give good results for experimenting with CI, but it's still an early project so would love feedback and more testers on.

Summary
The article discusses Chunkback, an open-source data backup tool that allows users to create secure, encrypted, and decentralized backups of their data. The tool utilizes blockchain technology and distributed storage to provide a reliable and privacy-preserving backup solution.
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