Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add mayank-io/mstack/plugin install fetchWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/mayank-io/mstack/youtube-download)<a href="https://agentmods.dev/skills/mayank-io/mstack/youtube-download"><img src="https://agentmods.dev/badge/skills/mayank-io/mstack/youtube-download/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/mayank-io/mstack/youtube-download"><img src="https://agentmods.dev/badge/skills/mayank-io/mstack/youtube-download.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00057 | $0.03091 |
| Opus 5.5 | $0.00023 | $0.01236 |
| Sonnet 5.5 | $0.00011 | $0.00618 |
| Haiku 4.5 | $0.00006 | $0.00309 |
Grade A, and why
youtube-download scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 22d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 278 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Download YouTube
Extract the transcript and metadata from a YouTube video. The script tries three tiers in order: youtube_transcript_api (no browser), the gstack browser's transcript panel, then Whisper over the audio.
Browser — always gstack, never headless
Browser work goes through the gstack browser, which holds the user's logged-in sessions. A fresh Playwright instance is logged out: it silently returns login walls or truncated content that looks like a successful capture.
B="$HOME/.claude/skills/gstack/browse/dist/browse"
"$B" connect # run from the target directory — another cwd spawns a second
# daemon and kills the headed session
"$B" goto "<url>"
"$B" js '<expression>'
Do NOT disconnect when done. browse disconnect tears down the daemon and
the logged-in sessions with it. Leave it running — the daemon is a shared user
resource, connect is safe to call again, and only whoever started it should
close it.
Never launch a headless browser. Not headless=True, not --headless, not a
fresh chromium.launch(). If gstack is unavailable, stop and say so rather than
falling back — a logged-out capture is worse than no capture, because it looks fine.
Configuration
There is nothing to configure. The browser tier drives the gstack daemon, which supplies the session; the script does not launch a browser or manage a profile of its own.
--profile and --headless are still accepted so older call sites keep
working, but both are ignored and the script says so on stderr. There is no
longer a chrome_profile_path or headless setting to read.
YouTube sign-in
The transcript comes out of whatever session the headed daemon holds — the user's own Chrome. If that session is not signed in to YouTube, the script prints a warning and continues: public videos are unaffected, but a members-only or age-gated one renders a watch page with no "Show transcript" button, which looks exactly like a video that has no captions. When you see that warning and the extraction comes back empty, the fix is to sign in to YouTube in Chrome — not to conclude the video has no transcript.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 22d ago Changed · +48 lines · +13 tokens per session 4c5cecd1e819
- 1mo ago First seen · 230 lines · 44 tokens per session scan A a684b1629efd
youtube-download is a skill published in the GitHub repository mayank-io/mstack (6 stars, last pushed 3d ago), licensed MIT. It adds 57 tokens to every session and 3,091 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-13.
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