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AI · November 19, 2025

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

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…

ChunkBack – A Fake LLM API server for testing apps without paying launched on November 19, 2025 with 6 votes, #2,995 of 9,796 launches that month and more than 75% of that year's launches.

What it does

ChunkBack lets you test your apps with LLM provider endpoints without having to pay for the providers - chunkback/chunkback

In the maker’s words, at launch

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…

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