ChunkBack
A Fake LLM API server for testing apps without paying
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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.
HN · launched Nov 19, 2025 · 6 upvotes (top 73%) · 0 views
Niche: api testing and mocking tools · 85 launches, 7 in the last 7 days ▼ -22% · Explore this niche →
Category and tags
- Horizontal
- Dev tools
- Developer
- Not AI
- Hobby / open-source project
Visit website ↗ Source listing ↗
More like this: all 85 launches in api testing and mocking tools →
Could you build this?
Yes It is a mock HTTP proxy/server mimicking OpenAI/Anthropic/Gemini streaming responses, which can be implemented in a day using Express, FastAPI, or similar frameworks.
Discussion
No comments on this launch.
Competitors
Other products that read as similar to this one : 229 launches clear the similarity bar, closest 8 shown.
Attention rank: #176 of 230 (itself plus its competitors, highest first, normalized so YC and Product Hunt are compared fairly).
Launched 20 days after the earliest competitor.
- An unmetered LLM API–$6/month, no token tracking, no limits · hn · 2026-07-06 · 12 upvotes · similarity 0.48
- ChunkHound, a local-first tool for understanding large codebases · hn · 2026-01-17 · 114 upvotes · similarity 0.47
- Mocktail · hn · 2026-08-14 · 25 upvotes · similarity 0.46
- LLM Test Server · ph · 2026-10-22 · 22 upvotes · similarity 0.44
- Tokenflood · hn · 2025-11-12 · 21 upvotes · similarity 0.43
- Mock Server Studio · ph · 2026-10-04 · 1 upvotes · similarity 0.43
- I'm tired of my LLM bullshitting. So I fixed it · hn · 2026-01-22 · 5 upvotes · similarity 0.42
- Why write code if the LLM can just do the thing? (web app experiment) · hn · 2025-11-01 · 436 upvotes · similarity 0.41
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