Putting the "clack" of a mechanical keyboard into your iPhone: a Korean developer's input method sells a lifetime one-time purchase off a single Instagram ad

A Korean indie developer made an iPhone keyboard called 쏘키 (Thokey). When you type, it plays recordings of real mechanical switches. In September he posted on a mechanical keyboard forum to find testers; in October he filled in the keyboard layouts Koreans commonly use and started running Instagram ads. Two months after launch, it hit #8 top-grossing in the Korean App Store's Utilities category. Below: what it sells, where people come from, why some people pay 19,000 won right after installing, and where you could break in.

A post at 3:30 a.m.

Sep 16, 2026, at 3:27 (Korean time), someone in the mechanical keyboard gallery on DCinside, Korea's largest forum, posted under the nickname 쏘키 with the title "형님들 기계식 키보드 앱 고쳤습니다" (Hyungnims, I fixed the mechanical keyboard app). The body was three lines: last time you said typing was laggy, I tried to fix it and it feels much better; I also added long-press to type double consonants.

The post got 6 comments. One said "Make one for Galaxy too," and he replied "I'll try if I have the time..!!" Another said "The keyboard is too slow, I keep making typos, 16 Pro," and he replied "Looks like there are still bugs, sorry ㅠㅠ, really thanks for the feedback." Three days later he posted again, titled "아이폰 기계식 키보드 앱 최종 최종" (iPhone mechanical keyboard app, final final), and someone commented "The app looks really good."

At that point it had been on the App Store for less than three weeks (8-27 listing), and the developer account "Paulus (KR)" had only this one app. Six weeks later, in October 31, it reached #8 in the Korean Utilities top-grossing chart. The top ten of the same chart also included NordVPN and Naver MYBOX.

What it is, and how it charges

쏘키 is an iOS custom keyboard. You turn it on in system settings to replace the original input method. Each keystroke plays a recording of a real switch. A switch is the mechanism under a mechanical keyboard key, and different switches sound and feel different. There's also a "damping mode" that lets you toggle between a muted "thock" sound and a crisp one, and you can adjust the vibration strength.

The free version has red and brown switch sounds and three basic themes. The nicer switches (black, blue, NK Cream, Akko Lavender) and themes like Liquid Glass, RGB Gaming, Strawberry Milk, and Banana Milk require the "Ssokey Pass." The Pass can be bought as a subscription (with a 7-day trial) or as a one-time lifetime purchase for 19,000 won, about $14.

The first line of the store page reads "From Cheonjiin(+) to Nara-geul, Vega, and single vowels, all supported." These are the Korean keyboard layouts Koreans use most on their phones. This line is where it differs from other "sound keyboards," which we'll get to below.

Traffic was an October thing

Source: App Store Korean chart and ratings, recorded daily.

The time distribution of reviews is clearer: of the 135 reviews visible, 18 were from September, 103 from October, and 14 from the first four days of November. As of 11-06, the Korean average rating is 4.88, with 52 new ratings in the last 7 days.

From the chart, the first wave may already be over. In the first week of November, the top-grossing rank fell from #8 to #21, and the top-free rank fell from the twenties to #41,11-06. Looking at the store page now, the top-free rank is #58. It could be that the ads were cut, or that people who wanted the lifetime version have already bought it (inference). The bar for the Korean Utilities top-grossing chart isn't high: most of the top 425 are older apps like VPNs, cloud drives, and cleaners, so a new app with only 200 ratings squeezing into the top ten suggests the lifetime version has sold quite a bit (inference). How much money it actually made can't be seen from the outside.

Where users come from

Step one: seed users came from enthusiast forums. The developer posted under the nickname 쏘키 on DCinside's mechanical keyboard gallery, collected feedback, and fixed bugs on the spot. The "last time" in 9-16's post shows he had posted before. Later, one App Store review was titled "쏘키형님 키갤러입니다" (Hyung 쏘키, I'm from the keyboard gallery), with the text: "I've always collected full-aluminum keyboards, and I never thought I'd see a phone keyboard you could customize too lol. Thanks for responding to feedback so fast in the early days and fixing bugs."

Step two: from October, Instagram ad buying became the main channel. The reviews mention "인스타" (Instagram) 8 times and "광고" (ad) 6 times. A few quotes:

• 10-19: "At first I saw an ad and got curious and installed it... after a week of trying it, I couldn't resist buying the lifetime version."
• 10-22: "I really saw it under an Instagram ad. As a keyboard nut... it's so cute, I don't feel like I wasted a penny."
• 10-25: "I have zero interest in keyboards, I just love keycaps, so I bought the lifetime version after seeing the Instagram ad."
• 10-31: "I bought it because of the ad, more satisfied than I expected. But what switch is the keyboard in the Instagram ad? I can't find anything similar."
• 11-02: "Saw it on Instagram and downloaded it, then paid right away lol lol lol lol lol"

The last two quotes show that the ad creative is videos of real mechanical keyboards being typed on, using sound to hook people. How much was spent and whether they're still buying ads can't be found.

Step three: some organic word of mouth. On Threads, someone posted "Recommended for people who like mechanical keyboards: 쏘키. Found it by chance, my ears are really enjoying it; the lifetime is 19,000 won, I'll buy it when I get paid." Others said "I think I saw it on Instagram or Threads," and someone bought one for their daughter too.

It's also worth noting the channels that didn't work: searching for "iPhone mechanical keyboard sound app" in Korean web results puts competitors ahead of it. We couldn't find any content about it on TikTok, X, or YouTube, and there's no media coverage. It's an app that only spread through small circles and feed ads.

Why people pay right after installing

It works as a main input method, not a toy. A repeated theme in the reviews: I thought it was a toy that makes noise, but it can replace the original input method. 10-21 One person wrote "I thought it was just a keyboard sound app, but it's so good I deleted Naver SmartBoard. Seeing Cheonjiin+ made me so excited I couldn't hide it." Another said "There are single vowels too, so moved," and "an app I've been looking for for years." One user said they kept making typos on their iPhone, "almost got in a car accident typing a short word," tried many input methods without satisfaction, and in the end 쏘키 "stopped me from breaking up with my iPhone."

The layouts were added step by step, and the update history makes this clear: in 10-12's 1.7.1 update it added Nara-geul and single vowels, and in 10-17's 1.7.3 update it added Cheonjiin+ and Vega. In other words, "a complete Korean input method" and the Instagram traffic push arrived at roughly the same time. Ads brought people in; complete layouts kept them and made them willing to pay.

The sound and look are addictive. The words in the reviews are "힐링" (healing), "ASMR," and "귀여워요" (cute): "makes me want to keep typing," "after changing the keycap design it feels completely different, healing, relaxing." You press a keyboard hundreds of times a day, and each press reminds you the money was worth it.

The price is low enough that you don't think twice. 135 reviews mention "평생" (lifetime) 35 times, with typical phrasing like "installed it today, paid right away" and "saw it and bought the lifetime version immediately." 10-30 One review says "Glad I found out before October ended and got the lifetime version," suggesting October may have had a limited-time lifetime price (unverified).

The developer iterates fast, updating almost daily. From mid-September to 11-03, the version went from 1.5 to 1.7.8, and in late October it shipped a release every two or three days: 10-23 added 35 themes and a clipboard, 10-25 added Chinese and Korean auto-correct, 10-28 added Thai, and 11-03 added a "theme workshop" where users make their own themes. Reviews: "I've never seen a developer respond to feedback this fast," "The Ssokey developer really works like an ox," "The replies don't look copy-pasted, I believe them."

Negative reviews exist too, concentrated on compatibility: it doesn't work in Instagram Stories, group chats, or search boxes, it lags in some apps, and Cheonjiin occasionally composes characters wrong. Frequent updates offset these, and for now that's holding up.

Who it's competing with

The sound people don't read Korean, the Korean people don't have sound. From 2026 7 to October, several "mechanical keyboard sound" apps appeared on iOS. Going by public ratings and chart data, only 쏘키 has produced revenue. I haven't seen anyone copy its Korean-language approach yet.

Where it goes next

It's already expanding on its own. The store page says it supports 58 languages; in the changelog, 9-24 added a "20-language keyboard", 10-12 added Japanese and Filipino, 10-25 Chinese, 10-28 Thai, and 11-03 improved the Japanese again. The Japan store just charted 11-06 on the Utilities Top Free chart, at #203, with only 5 ratings.

There's one piece it hasn't done: Android. In the September thread where someone asked "make one for Galaxy too," its reply was "if I have the bandwidth." Korean users probably use Galaxy at a much higher rate than iPhone (inference; public market-share data usually looks like this), and the Android equivalents don't read Korean.

If it were you

Quick take: You can follow this, but don't copy its iOS Korean version. The parts worth building are the two it hasn't covered: a Korean Android version, and a language it only "supports" without doing well.

Who it's for: People who have built an input method before, or are willing to take on the work, and who care about keyboard layouts at a native-speaker level for the target language. For Korean that means things like 천지인 and 나랏글; Japanese uses flick input, Chinese uses Zhuyin and Cangjie. Ideally you also know how to cut vertical short videos and have run Instagram or TikTok ads. One or two people is enough.

Who it's not for: Anyone who only wants a "keyboard skin that makes sounds." That route already has five or six iOS apps, none of which took off. The difference is whether it can be someone's main keyboard. Also skip it if you won't ship updates every week: input method reviews are all about compatibility bugs, and 쏘키 only kept things under control by shipping every two or three days.

How to build it: First get one language's core layout complete and smooth, with no composition errors and no dropped keys during fast typing. That's the retention foundation. Sound and themes come after. Record sounds from real switches, offer a few for free, and put the good ones in the paid tier. Copy its pricing: a subscription with a 7-day trial, plus a lifetime one-time purchase priced like a cup or two of coffee. On Android, custom keyboards have fewer restrictions and sound latency is easier to manage, so this may be easier to get right (inference).

How to get users: Two phases. In the seeding phase, go to the relevant enthusiast communities: in Korea, the DCinside mechanical keyboard gallery; in Japan, the custom-keyboard circles on 5ch or X. Post under a fixed handle, collect feedback in public, fix bugs on the spot, and let the first users vouch for you in the comments. In the scaling phase, run Instagram ads showing real mechanical keyboard typing videos with sound on, so people watch and want to ask "what switch is that?"

When to move: The sooner the better, ideally before 쏘키 ships its own Android version or its Japanese version starts gaining traction in Japan. Two signals to watch: its name showing up on Google Play, or its Japan ratings climbing every day.

What would mean you got it wrong: ① 쏘키's Korea Top Grossing drops out of the top 50 Utilities within a month and its rating growth stalls, meaning this wave was pushed by ads and stops when the spending stops, so lifetime purchases can't sustain ongoing ad spend; ② it launches a Korean Android version on Google Play and it gains traction within a month, which closes the Android gap; ③ it grows in Japan without paid ads, showing that "sound + local layout" is easy for it to replicate across languages, leaving followers little room.

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Data and sources: App Store Korea and Japan daily charts, ratings and reviews (as of 11-06); App Store Korea store page and update log (11-06); DCinside mechanical keyboard gallery posts 9-16 and 9-19 (gall.dcinside.com, mechanicalkeyboard); a recommendation post from Threads @x_eun.j; competitor ratings from the public App Store API (11-06); Android competitor install counts from Google Play. No public data exists on Instagram ad spend or how many lifetime versus subscription purchases were sold.