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Hi, this is Momoki from Developer Success Team.

We held LINE DEVELOPER DAY 2020, LINE’s technology conference, for three days from November 25 to 27. First of all, I would like to thank everyone who participated, all the guests and internal speakers, and everyone involved in the organization of the event.

LINE DEVELOPER DAY 2020 was our first online event due to the spread of COVID-19. In this article, I will look back at the trends in registration, participation, and viewing of LINE DEVELOPER DAY 2020, along with various figures, by excerpting and editing some of the content from the internal report.

Event Results

At LINE DEVELOPER DAY 2020, 180 employees from LINE and its group companies and 35 external guests, for a total of 215 people, took to the stage and presented a total of 155 sessions across 6 tracks over 3 days. In total, 3,965 minutes (66 hours and 5 minutes) of content was delivered.
With the exception of a few, archived videos and presentation materials are available, so please take a look when you have time.
*Archived videos and presentation materials can also be watched and viewed from the detail pages of each session on the official website.
*Archived videos in Korean are available for the 25 sessions where the speaker’s presentation language was Korean.


As of the end of the event on November 27th, we had 9,980 registered participants. Of these, 3,863 (38.7%) were from Japan and 6,117 (61.3%) were from outside of Japan. While the event attracted a large number of participants from within Japan, there were more registrations from overseas than expected.

The participant countries and regions other than Japan were Indonesia with 2,112 participants (21.2%), South Korea with 1,930 (19.3%), Thailand with 1,006 (10.1%), and Taiwan with 753 (7.5%). The number of registered users in Indonesia was the second largest after Japan, owing to the strong relations formed with the local technical communities thanks to the DevRel team in the Indonesian office. We also conducted pilot promotions in Singapore, India, and some states in the U.S. where we do not have a development base, but these did not have much of an effect (figures are included in Other).

The following are the attributes of the registrants who filled out the registration form: 1,996 (20.0%) were server-side Engineers, 1,765 (17.7%) were students, and 1,063 (10.7%) were frontend engineers.


The total number of participants (IP count of access to the live pages) for the 3 days of the event was 15,116 and 11,997 unique participants/viewers. Compared to last year when the event was held as an offline event, the total number of participants increased from 3,000 to 15,116 (504%), and the number of unique participants increased from 2,200 to 11,997 (543%).

As a trend, about half of the participants/viewers were from Japan. In Japan, the number of participants exceeded the number of registered participants, partly because the event allowed unregistered and unlogged participants to watch the broadcast. On the other hand, in other countries and regions, the number of participants was about 40-60% of the total number of registered participants, and there were many people who registered but did not actually participate.

The average viewing time per participant/viewer was 1:02:23, and the average number of watching sessions per participant/viewer was 4.66.

The total number of viewers for the CTO’s Keynote was 3,129, with 1,336 viewers at the 5-minute mark and 1,610 viewers 5 minutes before the end. The top 10 sessions in terms of total number of viewers were as follows: Day 1, especially the AI/Data track, received the most viewers due to the high concentration of attendees on day 1.

Top 10 most watched sessions

DayTrackTitleTotal viewers5 mins after session started5 mins before session ended
1CTO Keynote – LINE DEVELOPER DAY 20203,1291,3361,610
1AI / DataLINE’s AI Product: The Future and Beyond1,685735861
1AI / DataThe past and future of machine learning research1,422678668
1AI / DataParallel WaveGAN: Fast and High-Quality GPU Text-to-Speech928529502
1AI / DataCLOVA Speech: End-to-End Speech Recognition in Everyday Life823485473
1AI / DataEnvironmental sound recognition with machine learning726412459
1AI / DataUnsupervised Separation of Speech for Smooth Communications685408360
2FrontendWhy Accessibility? The Reasons and How to Incorporate Solutions673350383
1InfrastructureHow LINE operates tens of thousands of physical machines672279313
1SecurityCross-platform Mobile Security at LINE632244265


Top 3 most watched sessions in day 2

TrackTitleTotal viewers5 mins after session started5 mins before session ended
FrontendWhy Accessibility? The Reasons and How to Incorporate Solutions673278350
FrontendType safety initiatives for LINE Securities front-end610240228
FrontendThe Evolving Web Ecosystem and Performance602284318


Top 3 most watched sessions in day 3

TrackTitleTotal viewers5 mins after session started5 mins before session ended
Product Management |Team & ProcessWhat Makes a Good PM? A Good Engineer? Insight from PM and CTO347192194
Product Management |Team & ProcessSenior Executives discuss LINE’s product management347198166
Developer Product | OSSWriting a Java library with better experience336152125


Average number of views by track for each day

Reaction Stickers

On the live page of LINE DEVELOPER DAY 2020, we provided reaction stickers to replace applause, cheers, and nods.


In total, 242,607 stickers were sent across all sessions (an average of 1,565 stickers per session), from left to right: CLAP: 122,706, UH HUH: 28,742, LGTM: 37,089, and CRAZY: 54,070. The sessions with particularly high sticker usage are as follows.

CTO Keynote – LINE DEVELOPER DAY 202034,32115,1093,5094,43911,264
LINE’s AI Product: The Future and Beyond21,2234,6466,0134,8885,676
How to quickly develop static pages in LINE20,3926,8112,2425,5795,760
Closing Talk: Looking Back on LINE DEVELOPER DAY 202013,9547,3632,0282,5212,042
The past and future of machine learning research8,6952,9483,4596531,635


For each session, we provided a function that allowed participants to rate their experience by selecting from the following four options: ” Very satisfied,” “Exceeded my expectations,” “Average,” and “Not satisfied.” However, we only received a total of 2,713 responses for all sessions (17.5 per session). Next year, we would like to improve the design of the website flow and the method of receiving evaluations for each session. For reference, the breakdown of the 2,713 responses for all sessions was as follows: 1,368 (50.4%) were wonderfully satisfied, 966 (35.6%) exceeded expectations, 325 (12.0%) were average, and 54 (2.0%) were not satisfied.

We also sent out a survey to the event participants about the whole event and received 551 responses. Thank you very much for your cooperation.

The overall satisfaction rate for the event was 198 (35.9%) for very satisfied, 261 (47.4%) for more than expected, 84 (15.2%) for average, and 8 (1.5%) for not satisfied. This is down from last year’s figures (65.1% very satisfied, 31.1% somewhat satisfied), but considering the fact that the event was held online and more people participated partially compared to offline events, we received a certain level of evaluation.

As for their intention to participate in the next event, 307 (55.7%) would definitely participate, 224 (40.7%) would participate depending on the content and timing, 13 (2.4%) would possibly participate, and 7 (1.3%) would never participate.

As for the amount and length of the content, while many (421/76.4%) said it was appropriate, about 1/6 (130/16.7%) said it was too much or too long. We would like to consider making the next one a little more compact by carefully selecting the content (as it was a lot of planning and management).

Websites that were planned and developed completely in-house received generally high marks: 251 (45.6%) very good, 252 (45.6%) good, 43 (7.8%) not so good, and 5 (0.9%) bad. On the other hand, we also received some comments about inadequate planning and functions, UI/UX, etc., and some parts were abandoned due to a combination of time and man-hours in the planning and development stages, so we would like to improve the website to provide a more pleasant experience next time.

Lastly, when asked whether they preferred online or offline, 362 (65.7%) preferred online, 132 (24.0%) preferred offline, and 57 (10.4%) were undecided, with the majority of respondents preferring or welcoming online.
On the other hand, about a quarter of the respondents preferred to hold the event offline, and we received many comments from both inside and outside the company that it was difficult to feel the excitement and enthusiasm of the event. The planning and administration team felt the same sense of excitement and challenge, and we are planning to consider a hybrid event that can be planned offline as well as online as a base for the next event.

Last but not least

That would be all for recap of LINE DEVELOPER DAY 2020. Thank you once again to everyone who watched and participated in the event.

This was the first time for us to plan and organize a large-scale online event with little precedent. On the other hand, it was also an opportunity for us to improve the quality of the event, the direction of the event, and many other improvements and issues. For the next event, the entire team will be working even harder to provide a more comfortable and valuable experience and time for everyone involved, including speakers, participants, and organizers.

See you at LINE DEVELOPER DAY 2021!