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Launch HN: Slip (YC S21) – Build and sell interactive programming courses
399 points by CoffeePython on Aug 11, 2021 | hide | past | favorite | 108 comments
Hi HN, I'm Kenneth and I'm the founder of Slip (https://www.slip.so), a marketplace for programmers to build and sell courses, including interactive elements like in-browser code execution, popular programming embeds (CodeSandbox, StackBlitz, Replit repls (Coming soon)), and videos.

Instead of spending 3 or more months building their own course platform, developers can use Slip to create engaging interactive courses and make more money faster from their knowledge

In January, I built vim.so in 3 days, and made $11k in my first month. I even did a Show HN for it (https://news.ycombinator.com/item?id=25846347). I was able to do it in 3 days because I had previously spent 3 months building an interactive course for Python fundamentals. That previous experience reduced the time it took me to build a new course, which was the only reason it made sense to do. 3 days of hacking was low-risk enough that when I had the idea for vim.so, it made sense to actually try and see.

The results blew me away and actually changed my life. If sales continue at the current rate, I'll make about $50k this year with vim.so. This experience gave me confidence that I could build something and sell it on the internet. It helped give me credibility as a developer, and got me connected with lots of other cool folks building cool things.

After launching vim.so, I started getting lots of inbound requests to build other interactive courses on various topics: Ruby, Git, Bash, etc. At first I thought I'd just build all these myself but quickly realized other folks could teach these topics at a much deeper level than I could. But why weren't they building these courses? It's because it's currently too hard to make an interactive programming course. After maybe the 5th Twitter DM asking me for an interactive Git course, I decided to start a platform that helps other devs do the same thing I did with vim.so.

The main tool in Slip is an online course editor that allows you to build a course with a variety of "block types". You can use markdown, videos, code snippets, figma embeds, CodeSandbox Embeds, and executable code snippets. Code executions happen in remote one-off Docker containers. Code snippets are built using the open-source Ace Editor react component.

The editor is free to use. We take a 10% cut of sales made via our site (plus processing fees). We handle payments via Stripe and accept and remit VAT taxes for the author. Slip also has features to help authors make more money with their courses. For selected courses, we can run a presale campaign. We also publish and feature courses directly on our site that meet a certain quality bar.

Some devs who have rolled their own interactive course platform have spent more than 6 months just on that part! If we can remove that 6 months of non-content work, more devs will be able to build better educational materials. I've met multiple folks making over 6 figures a year teaching programming courses. Slip will be a success if we can help many more people do that, a lot more easily.

If you have any experience building educational programming courses or ideas on what programming courses are lacking today, or have any thoughts to share, I'd love to hear from you!




A great example of starting something to solve a real problem that you faced yourself. If you had not started vim.so, you probably wouldn't realize this problem exists. You did things that don't scale with vim.so and now you are doing something which hopefully will scale. All the best.


The Slip approach for interactive courses is what is missing in most of learning platforms. For developers the learning process happens when you start coding not by watching videos. But most of the platforms like Udemy they only support text and video materials. We actually wrote an article about importance of learn by doing https://dev.to/corpcubite/why-learn-by-doing-is-important-5a... hope you find it helpful.


Hey this looks really promising! I'm thinking about making an intro to SQL course with my own spin on it. I went ahead and signed up as an author and have had a couple of issues so far:

1. The first time I clicked the magic link in the login flow took me to another login prompt. I re-entered my email but got a warning that I was requesting another link too soon. I went back and clicked the link again and was logged in right away.

2. Once logged in I see an empty page at https://app.slip.so/author - there is the side nav, but nothing in the main well.

3. I did notice a couple of console warnings around cookie attributes: Cookie “__tld__” will be soon rejected because it has the “SameSite” attribute set to “None” or an invalid value, without the “secure” attribute. To know more about the “SameSite“ attribute, read https://developer.mozilla.org/docs/Web/HTTP/Headers/Set-Cook...

I was also wondering for the SQL course if it would be feasible to stand up an in-browser sqlite database via sql.js and/or make an API call out to a service to stand up a database for student use.

Congrats on the launch and keep me post if this could be a viable course for your platform!


An additional first-run issue - after I got logged in (two links to do so?), the dashboard loaded. I click 'Add Course', and I get a box that says that happened, but no row on the course table. A reload shows the course created.


Yeah, we have an open ticket for that :) i think a better flow would be to just take you straight to your course when you click add course


Hey Reilly, we're looking at the cookie/registration/login flow issue rn.

we plan on adding support for sql courses :)


This issue should be fixed now! You may have to clear your cookies


Confirmed I was able to login directly from the email link and the cookie warnings are gone. I did see a brief flash of the login screen but then was immediately redirected to the app. Thanks for fixing this. Also I am able to create courses now, but that was fixed earlier.


How amazing...great job sir the site/app looks very promising!

Being a mid-50s dev with 35 years of programming experience, I'm finding ageism (or something) blocking my ability to get hired these days, so teaching is something I've been seriously thinking about. Your platform could very well be an ideal way to explore this path.

So a practical question...do you have any way to gauge course interest before one spends the time creating it as to make sure there will be a profitable number of students when the course starts?

As someone who is needing some income, I would hate to blindly spend a few weeks creating a course on, say, LAMP-stack + Bootstrap webapp development...only to find out that only 2 people are interested in this tech and I just spent a month to make $100 bucks or whatever.

I'm sorry if this is perhaps coming across as "crass" or something like that with simply focusing on the income side of things, but in general having a list of course topics that potential students have expressed interest in sure could be a useful thing to help one build courses that people actually want.

Anyway...congrats on the launch. So far the site seems really easy to use (LOVE the single email registration/login prompt! You have no idea how much I've argued for this sort of thing with past clients) and hopefully this will be the start of something mutually beneficial.

[edits]


It would make sense for the site to add requested topics to be covered and allow users to upvote/+1 them. That would give content creators some idea of the demand for those courses.


not crass at all! People who want to get paid for teaching valuable knowledge should get paid.

We have a presale feature available for select authors that we think are promising. We're going to formalize the process for getting selected soon but in the mean time a good way to gauge interest is to try and promote the idea of your course to any type of audience you might have. An email list is a decent idea for gauging interest


Good idea. Please consider generating websites from the courses to allow people to "white label" this. Alternatively, offer iframes or an api - a kind of headless CMS. This would allow course creators to feel comfortable not being so locked in.


Yeah we experimented a bit with this idea but the overwhelming feedback we kept getting is that devs wanted help with distribution more than they wanted to host a course on their own site.


Congrats! Some quick thoughts, then I've got a few questions for you...

Let's face it, there are many platforms out there already which are ideal for publishing a programming course. There are obviously pros and cons with each.

I'm glad to see Slip has such a straightforward and open revenue model. Some course platforms work on a royalty model where you are paid by minutes of your course videos watched... which can make it difficult to estimate how much you'll earn for all your hard work.

It's also nice to see that you're handling taxes and VAT obligations. Few do that. Udemy springs to mind as a platform that also handles tax, but there are others. I think going forward that more and more platforms will need to help their merchants handle tax, so kudos to you for thinking about it from the start.

Some of the platforms like Scrimba.com, Tuts+ and egghead.io are invite-only. I'm really glad to see you didn't go that route. However, those platforms will tell you they do it to ensure course quality and happier outcomes for students.

Which brings me to my questions...

Q1) Since you've created an open course marketplace, how do you plan to ensure course quality?

Q2) In the spirit of openness and transparency, I'm not seeing any links to terms of use, privacy policy, or policies that apply to instructors (licensing, payouts, dispute resolution, etc). For example here's Udemy's Instructor Terms (https://www.udemy.com/terms/instructor/) which references their promotions policy and various instructor obligations. Are your versions of those documents still in the works? If they already exist, are they only visible after you register (that would be an anti-pattern, but maybe there's a good reason)? Are you planning to make those viewable before someone signs up to the service?

Q3) Programmers aren't always natural course creators and effective teachers. Are you planning in the future to offer educational materials to help guide programmers on best practices for planning, producing, and publishing their course?


Q1) Right now, we're manually approving/denying courses for publishing based on a subjective quality bar. Our aim is to be more of a premium course marketplace for career developers.

Q2) Ah yeah we have a ToS, i'll add it to the home page rn. It's still evolving.

Q3) Yup we want to help more developers realize they can be teachers. Figuring out how to better take a dev from Never teaching -> Making money while creating real progress in their students, is a big goal


This looks awesome! Hope it works out for you. Could also see this becoming a B2B situation sometime down the road where engineering teams could use this as a knowledge base. That could also be really useful.


Yeah we’re hearing that more and more lately! Definitely think there is something there


It’s great to see you scratching your own itch as a developer, and opening up the same tools for other devs. Almost all learning platforms were built with generic tools (like video or text tutorials), built by non-engineers.

I can see this approach scale beyond just tutorials: at Uber, we had an in-house interactive platform called codelabs we used for onboarding for new systems. It was dead simple to use and engineers created a lot more helpful materials that were easier to understand. Slip reminds me of this approach as well.

Best of luck!


I've had a few folks already ask if we would build an in-house version for tech onboarding. It's an interesting idea!

Cool to know other companies are already building things like this in-house. Thanks!


This is awesome! I've been slowing building out chapters for Advanced Typescript and React Architecture courses, but I've hesitated to put too much time in since launching was always a bit of a pain.

Do you have a roadmap for supported languages yet? I saw node, but I'm curious about when Typescript will be added as well.


Looks good, but since I am more of a devops person, I must ask 2 things:

- What is the scope? E.g. only some predefined programming languages or say, Puppet is also OK?

- Who decides the pricing of a course?


Rn there is support for a handful of programming languages. We're going to add repl embeds which should unlock more language functionality and let you teach a puppet course.

You decide pricing but we will give feedback on our thoughts on the price you pick. The marketplace is a curated one, so we'd have to approve it.


I tried out the beta as well as the precursor to this product (to learn Vim). Learning programming works best when one can interactively learn.

Congrats on the launch.


cool! thanks for the support. It's been super fun on my side to see this small idea of teaching folks vim evolve into something that helps other devs earn money :)


Is your platform limited to support for certain programming languages only, or can a user create tools that support new programming languages?


Fabulous idea. I've taken numerous courses through Udemy, currently taking one to upskill in React, and I've found a big gap to be the lack of interactive exercises (where the real learning takes place).

I'll definitely have a look. Good luck!


Thanks! Yeah we've heard that same type of sentiment from lots of folks.

Definitely need the feedback loop to learn programming skills effectively.


Please try out course - https://altcampus.school. It's not ineractive in browser but solves the core of your problem in a different way.

Please try it out, would love to get your feedback.


I’m a course developer on a closed-access learning platform for a year. I love slip and have been following you from the beginning.

I think import/export in Markdown would be a killer feature, in particular because it then makes things super easy to synchronize with GitHub, which is a must to version a course. And also, it enables to collaborate easily.

Does the editor enable collaboration? I mean, more than one writer?

A low hanging fruit maybe: may code blocks come with already loaded, popular code formatters / linters? And also text blocks with spellcheckers? I think this would benefit the editor.


Collaboration is an interesting idea but hasn't been requested yet. import/export has been requested a lot and will most likely be added at some point.

love the idea on code formatting/linter/spell checkers


>We take a 10% cut of sales made via our site (plus processing fees)

That's a very generous offer. One of the sites I use to sell my ebooks takes 20% (includes processing fees, but still higher than 10%+fees).

>We handle payments via Stripe

Does it mean payout is via Stripe too? I only have Paypal as an option.

>You can use markdown, videos, code snippets, figma embeds, CodeSandbox Embeds, and executable code snippets.

Can you import/export this as a text file? I write my ebooks in markdown, wondering if there's a way to easily adapt it.


We don't support Paypal (yet?). We payout via Stripe.

You can't import/export yet but do plan on adding that


Looks great! The front page is very inviting and friendly for course creators.

I don't if how someone who's looking to buy a course would feel about that. Have you use tested it?


Yeah we're definitely focused more on the supply side right now!

We want to be the easiest tool for developers to create awesome and engaging courses.

In the future, as we start getting more courses published, I imagine we will probably swap the home page to be more course taker focused.


Awesome work on the app and the site for it! What did you use for the WYSIWYG editor? I've been playing around with an editor for something else and settled on Slate after doing some research into the available libraries. I've heard other people have had success with ProseMirror as well for this kind of thing


The text portion is tiptap.dev!


This looks awesome!

One question though (and this is a question I've had for a while with all these ed-tech startups) - how do you ensure the quality of the courses outside of plain ratings? What's the guarantee that the course creator has explained things in a way that will help someone learn effectively?


Manual review by our team rn :)


I'd love to see one of those feature comparison charts to see how it stacks up against the competition.

Reason is: it is too early to help with discovery now but it is going to take off, one would want to get in early to benefit from the growth.


Yeah we can probably add something like that soon. Right now we're a tiny team (2 people!) and we're pretty focused on just making our product better and helping existing users.

I can see the value of showing how we are differentiated though!


I think you could whip something up in an hour (30 min to write and 30 min to style it). I was thinking:

------ handles payments --- video lessons --- interactive

Udemy ------- Y ------------- Y ---------- N

Slip ------- Y ------------- Y ------------- Y

XYZ ------------- N ------------- N ------------- Y

etc

ugh, formatting is a challenge even here


hmmm, I think you should be able to use four leading spaces on HN to get monospaced text:

    | class | handles payments | video lessons | interactive |
    | Udemy | Y                | Y             | N           |
    | Slip  | Y                | Y             | Y           |
    | XYZ   | N                | N             | Y           |
edit: sweet! worked like a charm


This looks really great, Kenneth! I was actually just investigating this last week; didn't see Swift support yet but I'm eagerly awaiting it ;)

I've considered building some tutorials for a backend framework I was working on, and it would be sweet if they were interactive.

Wondering if it would be feasible to have a server running in the one off docker containers so that people could run some simple requests on it to see how it works. It would also be sweet if it could run a simple SQLite database so users could play around with the ORM components as well.

Congrats on the launch & I'll be following this!


Thanks Joshua! Yeah we don't have support for it quite yet! But plan on supporting all kinds of really neat dev workflows for courses :)


Really cool. I'm interested in writing a quick course/tutorial on the website to teach something.

Is it possible to get an image type? Or the ability to paste a link to an image.

It's not clear how to add an image from the Markdown.


we don't have image support yet but are going to add it very soon! We're using the https://www.tiptap.dev/ as our markdown editor and haven't added the image functionality just yet.


Is it intended that the homepage flashes colors? It's quite offputting.


Nope, that's unintentional. I'm not able to see your gif. But if you let me know your browser/OS/device I can take a look and fix it :)


The "Start Building Your Course For Free Today!" button and TOS button are both just white strips in Safari on Mac.


Same for me (chrome on windows)


Seeing the same thing, I captured it here: https://www.youtube.com/watch?v=9rj7SuJgs5E

for whatever reason the recordit link does not work for me.

I am using latest Chrome on Ubuntu 20.


Thanks for the YT link, not sure what was wrong with my recordit link.

MacOS Chrome Version 92.0.4515.131 (Official Build) (x86_64)


Don't think anyone has asked this yet but who maintains ownership of a submitted course?

For example could someone submit a course but also continue selling it via gumroad or another competing platform?


The author maintains ownership and can sell the content on other platforms if they want. I'll make a note to add this language into our ToS


Like the idea, but the website is broken:

* Help Video doesnt play

* When I click on the example, nothing happens

Using Chrome

Im a bit hesitant trying out a new site with basic functionality broken-- will my customers see the same problems?


I'll have to look deeper into the video playing issue and why that's not working.

Going to remove the example button. It's a relic from the old site/system.

We're a couple month old startup with 2 folks :) the upside is that we're super responsive to customer feedback and can fix things a lot faster than a giant corp


http://www.vim.so/ currently says "503 Backend is unhealthy"


Hmm not seeing this on my end! Did it happen on a certain page?


A bit unrelated question: can you share more about the experience as a solo founder and the application process to YC as solo founder?


Hey James! It was the same as any other YC application :) the process is the same for everyone.

- open application that anyone can submit - get an interview or don't get one - if you get the interview, you get 10 min to chat

They did ask me why I didn't have a cofounder and I told them the reason. The reason being that I wasn't close enough with anyone that was passionate about the same idea and was available to do a startup.


Thanks for the update!


Looks good! How does Slip compare to educative.io?


I've looked into using educative.io for course creation. There is a little bit more of politics involved when creating the course because of the expectation of high quality code. Also they use internal Docker tools to be able to create the interactive coding environments.

Slip, which I am using right now, is more straightforward and the ability to have code snippets in line which flows with the material is awesome.

Also, Slip is working on integrating with multiple platforms (StackBlitz, Figma, Repl, CodeSandbox) so we can leverage those platforms as well.

Both have a great offering and creating a course is "free" so would recommend giving both a try if you're looking to create a course.


Great question! It's similar.

We're a brand new startup. Only a few months old and we're currently a team of just 2 people.

One way we plan to differentiate is by being the easiest tool to use on the author side.

We've seen some early users already spend 10s of hours in their course per week which is really promising.

We're actively thinking of ways to transform awesome developers into great course teachers.

One hack we found was that a lot of great devs don't realize how valuable their knowledge is. We added a presale feature to encourage our most promising authors to build an amazing course.


Not op but afaik all courses from educative are from them, you can submit your own on slip


The last time I checked, they allow others to create a course, but needs to be approved by them.


Well done man!

You're doing great things with Slip and I think there is a big gap in the market here.

If anyone wants to know more about Kenneth, I interviewed him recently: https://www.nocsdegree.com/six-figure-software-engineer-sala...


Thanks pete! it was great going on your pod :)


cool but I like being able to google and learn without paying... I fear platforms like this will inflate my exploration cost


We plan to let authors create some free content too :)


FWIW... quick feedback:

1. Please add one sample course (demo)

2. Login vs Register is confusing

3. You may want to differentiate teacher vs student dashboard


1. In the works 2. We'll improve this 3. We'll do this too :)


Thanks for sharing the story Kenneth!

I’m on an adjacent path but my focus is on the filming & producing of video courses rather than the platform (I just use Thinkific) but it’s cool to hear how the demand from your audience led to the creation of your company!


This looks excellent, I would have definitely used it back in the day when I was creating programming courses. But is there a way for this to be a venture-scale company? At first glance, it seems better suited to be a lifestyle business.


Definitely think there is a path :)

Think of the economic value of leveling up millions of engineers!

A more top down approach would be to just look at competitor revenue in the space. Udemy, Coursera, etc. Multiple companies doing multiple hundred millions of revenue per year


I only see three courses. vim.so is not even on the list. Am I missing something?


vim.so is what I built prior to Slip. It wasn't built on Slip


Looks fantastic!

A bit of apples and oranges but I am looking for alternatives to Moodle which is the granddaddy of LMS - learning management systems.

I have to integrate youtube videos, quizzes, interactive learning materials, etc.


Looks great, congrats! I’m curious, how do you guys handle VAT taxes? Also, I didn’t know about the .so TLD; did you choose it because the .com alternative was already taken or because of other reasons?


We use Stripe Tax to calculate the taxes but we have to remit them ourselves since Stripe doesn't take care of that side.

yeah the .com wasn't available lol


You wrote this Launch HN too soon in my opinion. No register link, I found it by luck. When I log in I can't create a new course. How do I get started?


There were a few bugs! The auth/login bug should be squashed :) You might have to clear your cookies and log back in

On the landing page, a few folks told us that the buttons for signing up are showing up as white blocks on safari. We're looking into those.


I am seeing this more and more e.g. educative, repl.it, etc. In a nutshell, I am curious as to what the tech stack is for creating this type of stuff.


I mean Web app is probably not interesting but they are using Next.js and Fastapi: https://twitter.com/KennethCassel/status/1392845888888913923...

For the remote code execution, they are spawning docker containers it seems like:

https://twitter.com/KennethCassel/status/1335314388824301569...

Guess it works with having a base image and just rebuilding it with the code that should be run. Code is passed via an api call from frontend to backend. This should make sure not the whole environment is rebuilt again because of the docker cache but only the code which has been submitted.

How the docker thing actually works is just my guess btw.


I hate to break it to them but docker is not security.


I am having a hard time finding the languages that courses can be designed for. Could you list them here or post a link on your site that shows them. Thanks!


The code execution snippets work in Python3 and JS. You can make React/Next.js/Angular/etc courses via Stackblitz/CodeSandbox.


Would love to be able to do this for more platform engineering oriented courses. Hope you can add Terraform (HCL) in the future.

Good luck!


I think those courses are already pretty good inside of cloud training software like cloudacademy.com

I see slip as a tool that allows indie devs like Wes Bos invent and experiment with new ways of teaching and competing with codecademy


love this framing. yeah i hope we can help the next 100 Wes Bos' learn that they can teach programming online while earning a great living.

The time-barrier is just really high right now to make an awesome course.


I think this will be possible once we add Repl embeds :)


This is a great tool! Keep the good work!


The see an example button on the home page just refreshes the page on both Firefox and Chrome for me on Linux


We removed it! That was a relic from the old landing page


Any plans for C++ support? I've had some ideas for making C / C++ courses.


I love this. Simple as that.


Is there a course I can try out? Everything on the site seems to be on pre-sale.


Not yet! We're still very early days but will have some courses published soon :)


Been following you on twitter since vim.so! Godspeed to you sir!


Very cool, please add C++! Would love to start making some courses


We built interactive SQL course and JavaScript course. https://academy.bigbinary.com/learn-sql


Do you support custom domains?


Cool idea! Good luck folks


This is fantastic


Suuuuper nice!!


Looks great!


not able to open it


Congrats Kenneth. We are also developing a hands on experience tailwindcss courses https://tailwind.academy using Stackblitz.




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