CLI to order groceries via reverse-engineered REWE API (Haskell)
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I just had the best time learning about the REWE (German supermarket chain) API, how they use mTLS and what the workflows are. Also `mitmproxy2swagger`[1] is a great tool to create OpenAPI spec automatically.And then 2026 feels like the perfect time writing Haskell. The code is handwritten, but whenever I got stuck with the build system or was just not getting the types right, I could fall back to ask AI to unblock me. It was never that smooth before.Finally the best side projects are the ones you actually use and this one will be used for all my future grocery shopping.[1]https://github.com/alufers/mitmproxy2swagger
HN · launched Mar 30, 2026 · 205 upvotes (top 3%) · 0 views
Niche: developer command-line tools · 226 launches, 5 in the last 7 days ▼ -67% · Explore this niche →
Category and tags
- Retail & commerce
- Dev tools
- Prosumer
- Not AI
- Hobby / open-source project
Visit website ↗ Source listing ↗
More like this: all 226 launches in developer command-line tools →
Could you build this?
No Reverse-engineering proprietary mobile/web network traffic using mTLS certificate interception and crafting an idiomatic Haskell client to handle authentication workflows and undocumented APIs requires deep protocol and security reversing skills.
What it would actually take: The author used tools like mitmproxy to bypass TLS pinning, dump mTLS certificates/keystores from Android/iOS apps, and generate OpenAPI specifications from reverse-engineered network traffic. The client itself is handwritten in Haskell, requiring type-safe HTTP client architecture (wreq/http-client) and strict crypto/keystore handling. Building this demands reverse engineering of network protocols and non-trivial functional programming.
Discussion
20 comments analyzed.
Competitors mentioned: Piknik and Flaschenpost, Kroger API, heissepreise (open source multi-retailer scraper), MCP alternatives
Concerns raised: Internal APIs break without warning when app updates, MCP wastes tokens, REWE blocked the tool/API immediately after launch, No standard for where MCP servers should be hosted for easy agent discovery, REWE has worst price/quality ratio compared to competitors
Feature requests: Compare basket prices across different supermarkets in region, Sort results by unit price standardized format, Create optimized shopping routes across multiple stores
Competitors
Other products that read as similar to this one : 48 launches clear the similarity bar, closest 8 shown.
Attention rank: #3 of 49 (itself plus its competitors, highest first, normalized so YC and Product Hunt are compared fairly).
Launched 141 days after the earliest competitor.
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- Coi · hn · 2026-01-20 · 225 upvotes · similarity 0.35
- Shop via CLI; for agents and software engineers · hn · 2026-10-27 · 5 upvotes · similarity 0.34
- Supermarket Offers in Denmark · ph · 2026-11-07 · 1 upvotes · similarity 0.34
- OpenAI CLI Proxy · ph · 2026-10-26 · 1 upvotes · similarity 0.33
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