yt-dlp "No supported JavaScript runtime could be found": what you lose and how to fix it

This is the full text:

WARNING: [youtube] No supported JavaScript runtime could be found. Only deno is enabled by default; to use another runtime add  --js-runtimes RUNTIME[:PATH]  to your command/config. YouTube extraction without a JS runtime has been deprecated, and some formats may be missing. See  https://github.com/yt-dlp/yt-dlp/wiki/EJS  for details on installing one

YouTube makes clients solve small JavaScript challenges before it hands over some formats. yt-dlp needs a JavaScript runtime to run them. The part people miss is "Only deno is enabled by default". You can have Node installed, and yt-dlp will still print this, because it won't use Node unless you ask.

We listed formats for 8 videos, once with no runtime and once with Node and the solver script, and compared the format IDs.

Format 18 was missing on all 8. It is the 360p MP4 with audio and video in one file, so it's the format that works without ffmpeg. If your script asks for -f 18, it now depends on a runtime.

Beyond that, the loss was small on this sample. On dQw4w9WgXcQ with no runtime, format 140 (audio) and format 137 (1080p video) both downloaded in full. One video, aqz-KE-bpKQ, lost seven more formats. Another, 9bZkp7q19f0, went the other way: the run with no runtime listed four formats (271, 313, 400, 401) that the run with Node didn't. We ran each setup once per video, and YouTube's answers can vary between requests, so treat that as noise until proven otherwise.

That is today's picture. yt-dlp calls running without a runtime deprecated, so don't count on it staying this mild.

We tested each setup on dQw4w9WgXcQ:

The counts here include storyboards, which is why they run higher than the table above.

The second row is the trap. You add a runtime, and the warning is replaced by two scarier ones. A runtime alone isn't enough: yt-dlp also needs the solver script, which is a separate package called yt-dlp-ejs. A plain pip install yt-dlp doesn't bring it in. The [default] extra does.

python3 -m pip install -U "yt-dlp[default]"
yt-dlp --js-runtimes node "URL"

To stop typing the flag, put it in your config file. We ran this with a config file holding the one line below, and the warning went away.

mkdir -p ~/.config/yt-dlp
echo '--js-runtimes node' >> ~/.config/yt-dlp/config

Deno is the only runtime yt-dlp enables by default, so once it is on your PATH there is no flag to add. Their installer is the usual route:

curl -fsSL https://deno.land/install.sh | sh
python3 -m pip install -U "yt-dlp[default]"
yt-dlp "URL"

We got our Deno binary with pip install deno (2.9.8) rather than that script, and yt-dlp printed Solving JS challenges using deno with no warnings.

yt-dlp also supports QuickJS and Bun through --js-runtimes. We didn't test those.

If you installed yt-dlp from a distro package, or you have a runtime but no yt-dlp-ejs, let yt-dlp fetch the script itself:

yt-dlp --js-runtimes node --remote-components ejs:github "URL"

In our run that downloaded yt.solver.lib.min.js from the yt-dlp/ejs releases on GitHub (0.8.0), and the warnings cleared. This runs code fetched at run time, so you may prefer the pip package on a production machine. yt-dlp's help says this flag isn't needed with the official executable, or with the right version of yt-dlp-ejs installed.

The same setting is an option on YoutubeDL. This ran for us and listed 49 formats, format 18 included:

import yt_dlp

opts = {"skip_download": True, "js_runtimes": {"node": {}}}

with yt_dlp.YoutubeDL(opts) as ydl:
    info = ydl.extract_info("dQw4w9WgXcQ", download=False)
    print(len(info["formats"]))

With no runtime at all, this still wrote the English subtitle file, with the warning printed above it:

yt-dlp --skip-download --write-auto-subs --sub-langs en --sub-format "json3/vtt" "URL"

So if subtitles are all you're after, the warning isn't your problem. Our guide to yt-dlp subtitles to plain text covers the cleanup, because the automatic files repeat lines.

A runtime also won't get you past a block. Sign in to confirm you're not a bot is a separate problem about your IP address, and it's common on cloud servers. We covered that in the bot check guide. We didn't run today's tests from a server, so we can't say how the format counts look from one.

If you're fetching text from a server and don't want to maintain yt-dlp, a runtime, a solver script and proxies, TranscriptFetch is the hosted route, and it's ours. You send a video ID or URL to the YouTube Transcript API and get the transcript back as JSON. You start with 50 free credits, which don't renew, and failed requests aren't charged.

curl https://transcriptfetch.com/api/v2/transcripts/video \
  -H "Authorization: Bearer $TRANSCRIPTFETCH_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"video":"dQw4w9WgXcQ"}'

It won't help if you need the video file itself. For that, yt-dlp with a runtime is the right tool.