I hope REWE is seeing this and offers an official MCP server. In the end we pay real money there. :D
I wrote a skill some time ago to support me with "agentic groceries" on my own - it's the future of shopping I would say.
My workflow:
- I paste in urls or text for receipts I will cook this week
- agent extracts the ingredients, calculates cups to ml and such, replaces meat with vegi ingredients, replaces some other things I prefer always (often also creates a nice markdown receipe at this steo I can put into Obsidian)
- check my list of favs, check search cache (so not every time the api is called, I'm a good netizen :D )
- ask me which items I have at home (no need to add to the basket)
- search rewe api for multiple candidates and let me choose.
- after each recipe I enter /new to start with fresh context
- also I have a list of things I buy every week
I still put everything manually in the basket in the end, but this is not the thing which is time intensive.
wazHFsRy 50 minutes ago [-]
This is also my exact workflow here. Thank you. I'm adding things that should be in the basket via Siri to my Obsidian notes. I also add recipes to that list or anything else. Then Claude checks that list once I want to do the shopping, looks through my favorites, and fills the baskets with all the items needed. I also use Claude to list the most frequently bought items for a template that always gets filled in.
Bewelge 6 hours ago [-]
Cool project, but have mixed feelings about publishing ever easier ways to access this API. They've locked down the API a while ago for a reason.
I do have a suggestion for your app though:
Have it compare your basket of goods across different markets in your region to show you the cheapest option.
I'm pretty sure this possibility is actually one of the reasons they locked down the API.
I've used Data from REWE in the past and made a comparison between a couple of cities in Germany (I believe it was Frankfurt, cologne, Berlin, Munich and Hamburg). Hamburg was by far the most expensive, often as much as 10-20% more expensive.
wazHFsRy 4 hours ago [-]
The existing project was a great inspiration and helped me figure out the mTLS stuff. I totally get your mixed feelings, though.
What I suspect though:
They mainly show current discounts. The REWE API exposes those as a separate list for each market.
There's around 3.5k markets and each can set their own discounts and has their own product catalogue with their own pricing.
So it would be 3.5k API calls to fetch all offers for all markets. Which is doable.
But fetching all products takes like 100 calls per market. It's quite a bit of data. And I think most supermarket don't publish their catalogue at all since they don't have delivery options.
aweiher 1 hours ago [-]
2.8 rating in Play Store sounds bad
duskdozer 5 hours ago [-]
>I do have a suggestion for your app though: Have it compare your basket of goods across different markets in your region to show you the cheapest option.
I'd settle for just being able to sort items by unit price... I'm sure this is a [regulation-]solved problem in Germany though
Bewelge 4 hours ago [-]
> I'd settle for just being able to sort items by unit price
What do you mean? The official REWE app and website provide just that.
> I'm sure this is a [regulation-]solved problem in Germany though
Not sure what you mean by that.
gigatexal 3 hours ago [-]
An aggregator like this that could surface the same good for the cheapest price all inclusive of delivery would be something I would pay for!
atollk 3 hours ago [-]
As a SWE at Rewe (at a completely different department), I can say that I find this pretty cool. I wonder if this is going to be a wakeup to management to relax the API restrictions.
aweiher 50 minutes ago [-]
Please pitch internally for an official Rewe MCP server.
This is the future of doing groceries. Let us login with our credentials and let us do the search/filling the cart with agents.
Totally fine to do the payment only on the web, so everyone can be sure they only order what was wished, and not 300 avocados.
rvz 2 hours ago [-]
You should tell them to charge for the API.
kleiba 2 hours ago [-]
...or to tighten them.
wazHFsRy 3 hours ago [-]
I mean, definitely leads to me buying more stuff on Rewe than before.
hk1337 2 hours ago [-]
This reminds me of pizza party cli app way back late 90s or early 2000
wazHFsRy 4 hours ago [-]
I want to add something else to this. In the process of writing this, I also played with formal verification and formally verified the suggestion engine, which was a really nice side discovery.
The basic idea is to write a prove in Lean4 and then test both the production implementation (Haskell) and the Lean implementation against random inputs.
Compare if the results are the same.
If that is the case -> you can be pretty sure the unproven production version is as correct as the proven lean version.
It can search for items, add them to the basket, picks a delivery slot and does the checkout.
With a little more scaffolding in markdown files, this now takes care of my weekly shopping.
Latitude7973 5 hours ago [-]
Even a CLI interface would be better than the sorry excuse of Asda's website. I wonder if entrusting an LLM is worth the trade off with the tedium of online shopping.
ramon156 4 hours ago [-]
Serious good use of an AI. Just let them do the grey area (like repeated purchase). I'd even let an algo pick better groceries for me. Cools tuff!
wazHFsRy 4 hours ago [-]
Absolutely. For example, I want to ask it: Suggest me some vegetables I haven't ordered in recent weeks or stuff like this, and this is all possible.
aprilnya 3 hours ago [-]
Could even ask it to find recipes and then have it buy the ingredients needed for them next time it's doing your shopping!
volume_tech 2 hours ago [-]
the mTLS part is interesting. they're using it not for security in the traditional sense -- REWE knows what their own app is doing -- but as a fingerprinting mechanism. the client cert is how they distinguish their official app from third-party access. the weak point is that the cert has to live somewhere in the app binary, which is why mitmproxy can intercept it. it's less about encryption and more about making ToS enforcement slightly harder.
zephyrwhimsy 3 hours ago [-]
Evaluation in LLM applications is still an unsolved problem. Most teams rely on vibes-based assessment. Rigorous evaluation frameworks that correlate with real-world performance remain elusive.
braedonwatkins 4 hours ago [-]
I remember a friend and I in college were looking into ways to do this in the US but major grocery chains here are pretty sensitive about their product data being accessible by open APIs and web scraping...
It would have been a cool project!
rmoriz 4 hours ago [-]
Surprised how little the B2C and even B2B e-commerce segment is providing API access for automation and agentic coding. One could easily set up rate limits, fraud detection and KYC checks upfront initial access.
PurpleRamen 17 minutes ago [-]
Normal customers are not paying for APIs, so there is little value in offering them for free, especially when it can be harmful. B2B sometimes does pay for them, but not always is it obvious from the outside that they even exist. Much commerce is also on tight numbers and thus kinda secretive about their stuff.
wazHFsRy 4 hours ago [-]
Yeah, absolutely. I think internally, everyone is cooking up some gigantic commerce. This is just bringing it to myself a bit earlier.
Bewelge 4 hours ago [-]
B2B:
Look at chefkoch.de
They do use the REWE API, and I'm guessing not without their knowledge
B2C:
Is it really surprising that a busines has no interest in providing more price transparency to their customers?
rmoriz 4 hours ago [-]
When Amazon launches an API everyone cries. Same story over and over. Even better example: TakeAway-Group. The perfect MITM.
Bewelge 3 hours ago [-]
Think it's context dependent whether it's a good or bad thing.
The owners of German supermarket and car companies are really the richest of the rich in Germany (okay and maybe the SAP guy on top). It would definitely be a net positive if someone manages to scrape and compare their prices.
In the restaurant market it's one player abusing many small players.
And honestly, I think the reason everyone cries when "Amazon launches an API" is because Amazon would not dare to piss off the German supermarket oligopoly.
traceroute66 3 hours ago [-]
> B2C: Is it really surprising that a busines has no interest in providing more price transparency to their customers?
Might I suggest you remove your tin-foil hat and consider that:
- 99% of REWE customers almost certainly have no clue what an API is
- 99% of the remaining 1% know what an API is, but their day-job involves messing with APIs, so they don't want to spend their weekend-time messing with the REWE API, they just want to do their shopping at REWE.
- The final 0.1% are those who come on HN and pretend its all some sort of big conspiracy to minimise transparency by $evil_corp. :)
If you think about it, imagine if REWE officially exposed an API B2C. This would mean they are obligated to provide support.
Do you really want the price of your shopping to increase because REWE now needs to find money to pay for a helpdesk for the millions of B2C API users ?
Businesses and services differentiating between B2C and B2B is nothing new, that is why the two different terminologies exist !
What next, you don't want to fill up your car at the petrol station (B2C) but you want to be permitted to buy a barrel crude oil direct from the drill and refine it yourself (B2B) ?
Bewelge 1 hours ago [-]
> Might I suggest you remove your tin-foil hat and consider that:
First up: Read and follow the rules. No need to insult me. Especially considering what you said shows that you both misunderstood AND misrepresented what I've said.
And frankly, my reasoning was simply saying "Company won't publicize internal info if they don't get an advantage from doing so". It's literally the same reason Google doesn't publish all of their source code. I'm struggling to see what part you are misunderstanding but it has to be something extremely basic to conclude I'm a conspiracy nut for basically stating "Company acts in their interest".
Opening an API to the public allows third parties to develop apps that can then be consumed by end-consumers. Not trying to be offensive here, but do you know what an API is? To conclude I meant every single end-consumers building their own app is at best disingenuously twisting my words.
Opening the API would allow new players like you and me to enter the market and take a piece of the pie. Why would a market, dominated and controlled by a few big players, opt for that? You don't even need to know that the German grocery market is incredibly price competitive, to understand that.
> If you think about it, imagine if REWE officially exposed an API B2C. This would mean they are obligated to provide support.
Can you provide a source for that requirement? I'm pretty sure you just made that up.
> Businesses and services differentiating between B2C and B2B is nothing new, that is why the two different terminologies exist !
At this point I'm entirely lost what you read in my comment. Yes I know. I specifically made that distinction.
> What next, you don't want to fill up your car at the petrol station (B2C) but you want to be permitted to buy a barrel crude oil direct from the drill and refine it yourself (B2B) ?
Yeah you definitely misunderstood something... What I said/meant:
The question: Why isn't the API open?
My answer:
For B2B I gave an example where the API is used by another German firm, providing an example that the API is indeed consumed B2B.
For B2C: They have no reason to do so. They have a well functioning app where you can order stuff. They have one of the bigger recipe pages (at least it does very well SEO-wise) in Germany where you can immediately order ingredients from a recipe. The biggest recipe page in Germany (chefkoch) offers a direct link from recipes to their order page. Maybe you're missing this info? Thinking it's an internal API to data that isn't exposed anywhere at all would somehow explain whatever you tried to say here. But again, if you're that uninformed, don't insult people.
traceroute66 40 minutes ago [-]
> Opening an API to the public allows third parties to develop apps that can then be consumed by end-consumers. Not trying to be offensive here, but do you know what an API is? To conclude I meant every single end-consumers building their own app is at best disingenuously twisting my words.
Here you are wrong too.
If you want to develop an app via an API that is only offered B2B, what do you do ?
Yes, that's right ...
You phone up REWE and negotiate a license to access to the B2B API to develop your application. B2B2C if you want to put it in simpler terms.
My original point stands. REWE clearly do not want to officially expose the API B2C, almost certainly for the exact reasons I already spelled out in my original post.
But no, its easier for you just to spread FUD, claiming "busines has no interest in providing more price transparency to their customers" just because they will not let you have access to the API as direct B2C.
danielszlaski 6 hours ago [-]
I love the idea of a CLI for groceries. Do you have plans to support 're-order' scripts or meal-plan integration? I can imagine a workflow where a recipes.yaml file gets piped into your CLI to automatically fill the cart with everything needed for the week. Much faster than clicking through a mobile UI.
wazHFsRy 4 hours ago [-]
Absolutely, that could just be a small script or something on top that calls the CLI tool
a012 5 hours ago [-]
It’s one step closer to have an agent to go shopping for my recipes or dinner, but hopefully unlike the Son of Anton
wazHFsRy 4 hours ago [-]
I am using it exactly like this. I tell Claude: "Add all things for this recipe to the basket."
kls0e 7 hours ago [-]
this feels a bit like Sandra Bullock ordering pizza in „The Net“, impressive
wklm 8 hours ago [-]
Nice! Do you know if the Austrian billa (REWE's subsidiary) is using the same api?
My friend works at Billa AT; I could ask her – but that would be cheating ;-)
stavros 5 hours ago [-]
What's the point of this comment!
Dominik1001 8 hours ago [-]
Very cool! Thanks for sharing, I’ll try it out.
Haskell is indeed an interesting choice. ;)
ramonga 6 hours ago [-]
Funny enough I was looking at rewe network requests for a personal app that suggests weekly meals and automatically orders the ingredients for you
wazHFsRy 4 hours ago [-]
Just pipe the items through this CLI, and you can save a ton of work :)
picografix 6 hours ago [-]
tell us more about it
son3tt 5 hours ago [-]
Really cool, but this is also how you end with 300 avocados and 500 L of detergent.
stavros 5 hours ago [-]
Well of course, how else am I going to make my Tideamole?
sigr_ 6 hours ago [-]
Really cool to see things still being built in Haskell! How do you find using it compared to some of the newer languages that have more modern tooling?
Did you implement your own OAUTH2 flow in haskell for this?
wazHFsRy 3 hours ago [-]
For me, Haskell is the language of 2026. Having an agent available if you get stuck with some weird type error is a blessing. It also helps with the tooling. Though the modern tooling with cabal is pretty good.
yakshaving_jgt 5 hours ago [-]
Does Haskell not have modern tooling? What would be considered modern in this context?
sigr_ 48 minutes ago [-]
it does through cabal and stack but its not as streamlined, quick, and versatile as tooling for languages like Golang or Rust imo.
I'm a huge fan of Haskell and I'm really exploring it as my primary language now that AI has gotten so huge, not just because it makes it easier but also because I can really lock down what I allow code to do (through pure functions, type checking etc) and so I feel a lot more confident in AI generated code
yakshaving_jgt 42 minutes ago [-]
Could you be specific? Saying it's not as "streamlined, quick, and versatile" is vague — I'm not really getting anything from that.
For context, I've been writing Haskell for quite a long time and I'm maintaining a few packages like Yesod.
tietjens 6 hours ago [-]
Love this! Super cool.
rvz 6 hours ago [-]
> Finally the best side projects are the ones you actually use and this one will be used for all my future grocery shopping.
Until it breaks in a few weeks.
wazHFsRy 3 hours ago [-]
I mean, fixing small issues is not a big deal – during my ordering sessions, if something comes up, I actually just let Claude create an issue for it, and then when I have time, I create a fix.
rvz 3 hours ago [-]
Well you don't control the API so it will still break.
zephyrwhimsy 3 hours ago [-]
[dead]
MORPHOICES 7 hours ago [-]
[dead]
Rendered at 15:20:41 GMT+0000 (Coordinated Universal Time) with Vercel.
I wrote a skill some time ago to support me with "agentic groceries" on my own - it's the future of shopping I would say.
My workflow:
- I paste in urls or text for receipts I will cook this week - agent extracts the ingredients, calculates cups to ml and such, replaces meat with vegi ingredients, replaces some other things I prefer always (often also creates a nice markdown receipe at this steo I can put into Obsidian) - check my list of favs, check search cache (so not every time the api is called, I'm a good netizen :D ) - ask me which items I have at home (no need to add to the basket) - search rewe api for multiple candidates and let me choose. - after each recipe I enter /new to start with fresh context - also I have a list of things I buy every week
I still put everything manually in the basket in the end, but this is not the thing which is time intensive.
Also there already exists this reverse engineered project: https://github.com/ByteSizedMarius/rewerse-engineering/
I do have a suggestion for your app though: Have it compare your basket of goods across different markets in your region to show you the cheapest option. I'm pretty sure this possibility is actually one of the reasons they locked down the API.
I've used Data from REWE in the past and made a comparison between a couple of cities in Germany (I believe it was Frankfurt, cologne, Berlin, Munich and Hamburg). Hamburg was by far the most expensive, often as much as 10-20% more expensive.
I really like your suggestion. I will put it in an issue and look into that. https://github.com/yannick-cw/korb/issues/4
Check out smhaggle app on Android
https://play.google.com/store/apps/details?id=com.smhaggle.a...
What I suspect though: They mainly show current discounts. The REWE API exposes those as a separate list for each market. There's around 3.5k markets and each can set their own discounts and has their own product catalogue with their own pricing.
So it would be 3.5k API calls to fetch all offers for all markets. Which is doable.
But fetching all products takes like 100 calls per market. It's quite a bit of data. And I think most supermarket don't publish their catalogue at all since they don't have delivery options.
I'd settle for just being able to sort items by unit price... I'm sure this is a [regulation-]solved problem in Germany though
What do you mean? The official REWE app and website provide just that.
> I'm sure this is a [regulation-]solved problem in Germany though
Not sure what you mean by that.
This is the future of doing groceries. Let us login with our credentials and let us do the search/filling the cart with agents.
Totally fine to do the payment only on the web, so everyone can be sure they only order what was wished, and not 300 avocados.
The basic idea is to write a prove in Lean4 and then test both the production implementation (Haskell) and the Lean implementation against random inputs. Compare if the results are the same.
If that is the case -> you can be pretty sure the unproven production version is as correct as the proven lean version.
https://www.dev-log.me/formal_verification_in_any_language_f...
It can search for items, add them to the basket, picks a delivery slot and does the checkout.
With a little more scaffolding in markdown files, this now takes care of my weekly shopping.
It would have been a cool project!
B2C: Is it really surprising that a busines has no interest in providing more price transparency to their customers?
The owners of German supermarket and car companies are really the richest of the rich in Germany (okay and maybe the SAP guy on top). It would definitely be a net positive if someone manages to scrape and compare their prices.
In the restaurant market it's one player abusing many small players.
And honestly, I think the reason everyone cries when "Amazon launches an API" is because Amazon would not dare to piss off the German supermarket oligopoly.
Might I suggest you remove your tin-foil hat and consider that:
If you think about it, imagine if REWE officially exposed an API B2C. This would mean they are obligated to provide support.Do you really want the price of your shopping to increase because REWE now needs to find money to pay for a helpdesk for the millions of B2C API users ?
Businesses and services differentiating between B2C and B2B is nothing new, that is why the two different terminologies exist !
What next, you don't want to fill up your car at the petrol station (B2C) but you want to be permitted to buy a barrel crude oil direct from the drill and refine it yourself (B2B) ?
First up: Read and follow the rules. No need to insult me. Especially considering what you said shows that you both misunderstood AND misrepresented what I've said.
And frankly, my reasoning was simply saying "Company won't publicize internal info if they don't get an advantage from doing so". It's literally the same reason Google doesn't publish all of their source code. I'm struggling to see what part you are misunderstanding but it has to be something extremely basic to conclude I'm a conspiracy nut for basically stating "Company acts in their interest".
Opening an API to the public allows third parties to develop apps that can then be consumed by end-consumers. Not trying to be offensive here, but do you know what an API is? To conclude I meant every single end-consumers building their own app is at best disingenuously twisting my words.
Opening the API would allow new players like you and me to enter the market and take a piece of the pie. Why would a market, dominated and controlled by a few big players, opt for that? You don't even need to know that the German grocery market is incredibly price competitive, to understand that.
> If you think about it, imagine if REWE officially exposed an API B2C. This would mean they are obligated to provide support. Can you provide a source for that requirement? I'm pretty sure you just made that up.
> Businesses and services differentiating between B2C and B2B is nothing new, that is why the two different terminologies exist ! At this point I'm entirely lost what you read in my comment. Yes I know. I specifically made that distinction.
> What next, you don't want to fill up your car at the petrol station (B2C) but you want to be permitted to buy a barrel crude oil direct from the drill and refine it yourself (B2B) ? Yeah you definitely misunderstood something... What I said/meant:
The question: Why isn't the API open?
My answer: For B2B I gave an example where the API is used by another German firm, providing an example that the API is indeed consumed B2B.
For B2C: They have no reason to do so. They have a well functioning app where you can order stuff. They have one of the bigger recipe pages (at least it does very well SEO-wise) in Germany where you can immediately order ingredients from a recipe. The biggest recipe page in Germany (chefkoch) offers a direct link from recipes to their order page. Maybe you're missing this info? Thinking it's an internal API to data that isn't exposed anywhere at all would somehow explain whatever you tried to say here. But again, if you're that uninformed, don't insult people.
Here you are wrong too.
If you want to develop an app via an API that is only offered B2B, what do you do ?
Yes, that's right ...
You phone up REWE and negotiate a license to access to the B2B API to develop your application. B2B2C if you want to put it in simpler terms.
My original point stands. REWE clearly do not want to officially expose the API B2C, almost certainly for the exact reasons I already spelled out in my original post.
But no, its easier for you just to spread FUD, claiming "busines has no interest in providing more price transparency to their customers" just because they will not let you have access to the API as direct B2C.
Haskell is indeed an interesting choice. ;)
Did you implement your own OAUTH2 flow in haskell for this?
I'm a huge fan of Haskell and I'm really exploring it as my primary language now that AI has gotten so huge, not just because it makes it easier but also because I can really lock down what I allow code to do (through pure functions, type checking etc) and so I feel a lot more confident in AI generated code
For context, I've been writing Haskell for quite a long time and I'm maintaining a few packages like Yesod.
Until it breaks in a few weeks.