Agent skill

Youtube Thumbnail

by magnus919 in magnus919/agent-skills

Design, critique, and test YouTube video thumbnails and preview cards for stronger, better-qualified clicks.

MITAuto-check passedMedia & Creative

Install Youtube Thumbnail

skills CLI
$ npx skills add magnus919/agent-skills --skill youtube-thumbnail -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install magnus919/agent-skills youtube-thumbnail --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/magnus919/agent-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/youtube-thumbnail .claude/skills/youtube-thumbnail && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
youtube-thumbnail
GitHub stars
115
Token cost
~1.7k tokens
SKILL.md length
875 words
Files
12 (incl. scripts, references)
Skills in repo
131
Repo updated
First seen
Licence
MIT

At a glance

Design, critique, and test YouTube video thumbnails and preview cards for stronger, better-qualified clicks.

  • Works in 7 steps: Ground the promise in the video. Inspect… → Design the title–thumbnail package. Keep… → Build a reference board, then translate.… → …
  • Developing thumbnail concepts
  • SKILL.md covers When not to use, Workflow, Integrity rules and Working templates, plus 1 more section
  • Runs Python scripts from its folder; calls python3

What it does

Youtube Thumbnail is an agent skill from magnus919/agent-skills. Design, critique, and test YouTube video thumbnails and preview cards for stronger, better-qualified clicks. Use when developing thumbnail concepts, pairing a thumbnail with a title, directing image creation, checking small-screen legibility, preparing a YouTube experiment, or diagnosing thumbnail performance. Do not use for general video editing, channel strategy, or artwork for another platform.

Its SKILL.md is about 1.7k tokens, which your agent loads only when the skill is triggered. The skill folder holds 15 other files, including scripts and reference files (for example `README.md`, `evals/evals.json` and `evals/trigger-queries.json`).

It sits in Media & Creative, covering Go-to-market strategy, Video production and Design review and critique. It works with YouTube. The repository describes itself as: Curated collection of AI agent skills for Hermes and other agent frameworks. The licence is MIT.

When your agent uses it

  • Developing thumbnail concepts
  • Pairing a thumbnail with a title
  • Directing image creation
  • Checking small-screen legibility

Example prompts

  • “/youtube-thumbnail”

Requirements

  • Python 3

Workflow steps

7 steps, taken from the first numbered list in SKILL.md.

  1. Ground the promise in the video. Inspect the supplied video, outline, transcript, title, and available image assets before inventing a…
  2. Design the title–thumbnail package. Keep the actual title beside every concept. State what the title explains and what the image adds. The…
  3. Build a reference board, then translate. Gather several references from the creator's own videos, relevant channels, adjacent formats, and…
  4. Develop three genuinely different concepts. Each should test a different visual hypothesis, not just a new font or color. For every…
  5. Make the strongest idea. Start from real, user-provided, or rights-cleared visual material where available. When generating or editing…
  6. Review the artifact as viewers will see it. Put the thumbnail beside its title and plausible neighboring videos, then inspect at full…
  7. Choose and learn with the right evidence. If eligible, use YouTube Studio's native Test & Compare and make the variants meaningfully…

What it can do on your machine

Read from SKILL.md and the folder at commit 22b4723. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Ships 2 files in scripts/ (Python), which the agent can run.

    Shell commands in SKILL.md call:

    • python3

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Youtube Thumbnail loads about 1.7k tokens when it runs, and up to ~6k if it reads all its reference files. Until then it costs about 105 tokens; SKILL.md has 875 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~105
When it runs · the whole SKILL.md, loaded when a task matches
~1.7k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~6k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.

SKILL.md

The full file from magnus919/agent-skills at commit 22b4723, republished under its MIT licence (© magnus919). 875 words, ~1,668 tokens.

Download SKILL.mdSave it as .claude/skills/youtube-thumbnail/SKILL.md (or your agent's skills folder). This skill also uses 11 other files; get the full folder from GitHub.
name
youtube-thumbnail
description
Design, critique, and test YouTube video thumbnails and preview cards for stronger, better-qualified clicks. Use when developing thumbnail concepts, pairing a thumbnail with a title, directing image creation, checking small-screen legibility, preparing a YouTube experiment, or diagnosing thumbnail performance. Do not use for general video editing, channel strategy, or artwork for another platform.
license
MIT

YouTube thumbnail design

Make the right viewer curious about a real promise the video fulfills. A thumbnail is packaging, not a performance guarantee: earn attention without misrepresenting the video, and judge the result by qualified viewing rather than clicks alone.

When not to use

Use this skill for YouTube thumbnail strategy and production. For general channel positioning or growth plans, use a channel-strategy skill. For artwork that is not a YouTube preview card, use the relevant image, brand, or publication skill instead.

Workflow

  1. Ground the promise in the video. Inspect the supplied video, outline, transcript, title, and available image assets before inventing a concept. If the video itself is accessible, use an appropriate transcript/video capability. Write one sentence for what the video actually delivers, who should care, and what evidence or moment in the video proves it. If those facts are missing and cannot be found, ask a small number of targeted questions; do not fill gaps with invented stakes, people, outcomes, or scenes.

  2. Design the title–thumbnail package. Keep the actual title beside every concept. State what the title explains and what the image adds. The image may create a question, reveal a striking result, show a meaningful contrast, or evoke a fitting emotion; it should not merely repeat the title. Text is optional, not a quota. Add it only when it makes the idea clearer or more distinctive at thumbnail size.

  3. Build a reference board, then translate. Gather several references from the creator's own videos, relevant channels, adjacent formats, and non-YouTube visual culture. For each, record the mechanism that earns attention (for example, scale contrast, reveal, gesture, visual metaphor, or an unresolved question), not just its colors or layout. Adapt the mechanism to this video's proof and audience; do not copy another creator's composition, branding, artwork, or likeness. Read design principles when the brief needs deeper concept development.

  4. Develop three genuinely different concepts. Each should test a different visual hypothesis, not just a new font or color. For every concept record:

    • the audience and viewing context;
    • the question or feeling it should create;
    • the single first-read focal subject or visual event;
    • the mechanism and video evidence that support it;
    • its title pairing and any short overlay text;
    • the truth, rights, identity, crop, and legibility risks. Prefer a clear, specific image over a pile of topic symbols. A face, exaggerated expression, text, arrows, and a bright outline are tools, not mandatory ingredients.
  5. Make the strongest idea. Start from real, user-provided, or rights-cleared visual material where available. When generating or editing imagery, specify the actual subject, action, perspective, contrast, and negative space. Do not invent factual evidence or imply that a real person did something they did not do. If exact text matters, typeset or correct it in an editor that allows glyph-level inspection rather than trusting model-rendered lettering. Keep the source asset unchanged.

  6. Review the artifact as viewers will see it. Put the thumbnail beside its title and plausible neighboring videos, then inspect at full export size, feed/card size, and a tiny preview. Ask a cold reader what they notice first, what they think the video promises, and what remains unclear. Use the upper-half mask only as an optional stress test if TV is a meaningful audience segment; test the actual surface because interfaces vary. It is a heuristic, not a platform rule. Run the bundled preflight and make visual corrections yourself. Read platform, policy, and export checks for dimensions, upload limits, and safety checks.

    bash
    python3 scripts/thumbnail_preflight.py candidate.jpg \
      --profile video --upload-device desktop --proof-dir proofs/

    The script checks file-level constraints and creates small-size proof images. It cannot judge whether the image is honest, compelling, readable, or on-brand; inspect the proofs. Read the script contract before using its flags.

  7. Choose and learn with the right evidence. If eligible, use YouTube Studio's native Test & Compare and make the variants meaningfully different. Its selection is based on watch-time share, not CTR alone; tests can be same-performing or inconclusive. If native testing is unavailable, record before/after observations as observational, not as proof that the thumbnail caused a change. Segment by traffic source and audience where possible, and check the video's opening retention for promise fit. Read testing and measurement before making performance claims.

Show full SKILL.md (179 more words)Show less

Integrity rules

  • Do not guarantee CTR, views, or growth; no design formula predicts a particular result.
  • Do not use misleading imagery, fabricated proof, unauthorized impersonation, or a title–thumbnail promise the video does not deliver.
  • Do not optimize a click metric while ignoring watch time, retention, audience fit, or the viewer experience.
  • Keep platform requirements distinct from creative heuristics. YouTube's current help pages are authoritative for dimensions, eligibility, and policy; check them again before upload because they can change.
  • Keep the final image and test record tied to the video and title version actually published.

Working templates

Completion criteria

A thumbnail job is complete when a truthful title–thumbnail package has been reviewed at realistic display sizes, the file passes the chosen export profile or its exceptions are disclosed, and the deliverable includes the selected concept plus any remaining uncertainty. If a test was not run or the data are inconclusive, say so; do not present a design review as a measured performance result.

© magnus919, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 11 other files (scripts, references) in youtube-thumbnail of magnus919/agent-skills.

  • SKILL.md
  • README.md
  • evals/evals.json
  • evals/trigger-queries.json
  • references/design-principles.md
  • references/platform-and-policy.md
  • references/testing-and-measurement.md
  • requirements.txt
  • scripts/test_thumbnail_preflight.py
  • scripts/thumbnail_preflight.py
  • templates/experiment-log.md
  • templates/thumbnail-brief.md

Open the folder on GitHubat commit 22b4723

Compare with similar skills

Youtube Thumbnail next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Youtube Thumbnail compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Youtube Thumbnail this skillmagnus919/agent-skills115—~1.7kAutomated safety check: PassMIT
Yt Dlp DownloaderMapleShaw/yt-dlp-downloader-skill2091 repos~1.5kAutomated safety check: PassNone
Media Downloaderyizhiyanhua-ai/media-downloader4031 repos~824Automated safety check: PassNone
Youtube Thumbnailhassancs91/claude-youtube-editor328—~2.1kAutomated safety check: NotesMIT
Shorts Video Makeruxjoseph/content-marketing-team107—~665Automated safety check: PassNone
Motion Video in Remotionooiyeefei/ccc495—~2.9kAutomated safety check: PassMIT

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Works with

Questions about Youtube Thumbnail

What does Youtube Thumbnail do?

Design, critique, and test YouTube video thumbnails and preview cards for stronger, better-qualified clicks. Youtube Thumbnail is an agent skill from magnus919/agent-skills. Design, critique, and test YouTube video thumbnails and preview cards for stronger, better-qualified clicks.

When should I use Youtube Thumbnail?

Youtube Thumbnail fits situations like: developing thumbnail concepts; pairing a thumbnail with a title; directing image creation; checking small-screen legibility.

How do I install Youtube Thumbnail in Claude Code?

Run `npx skills add magnus919/agent-skills --skill youtube-thumbnail -a claude-code`. Or copy the skill folder (youtube-thumbnail in magnus919/agent-skills) into .claude/skills/youtube-thumbnail in your project. Claude Code loads it when a task matches its description.

How do I install Youtube Thumbnail in Codex?

Run `npx skills add magnus919/agent-skills --skill youtube-thumbnail -a codex`. Or copy the skill folder (youtube-thumbnail in magnus919/agent-skills) into .agents/skills/youtube-thumbnail in your project. Codex loads it when a task matches its description.

Can I use Youtube Thumbnail in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add magnus919/agent-skills --skill youtube-thumbnail -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/youtube-thumbnail, .gemini/skills/youtube-thumbnail, .github/skills/youtube-thumbnail and .opencode/skills/youtube-thumbnail in your project.

What does Youtube Thumbnail need to run?

Going by SKILL.md and its folder, Youtube Thumbnail needs Python for the scripts in its folder and the command-line tools its instructions call (python3). Our summary lists: Python 3.

Does Youtube Thumbnail access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Youtube Thumbnail safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. The check reads SKILL.md only: the scripts in the folder are not scanned, so read them before running anything.

What licence does Youtube Thumbnail use?

Youtube Thumbnail is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Youtube Thumbnail use?

About 1.7k tokens (SKILL.md is roughly 6.7k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 4.3k tokens, read only when the agent opens those files.

What are the alternatives to Youtube Thumbnail?

Skills that share tags, products or a category with Youtube Thumbnail: Yt Dlp Downloader (MapleShaw/yt-dlp-downloader-skill, 209 stars), Media Downloader (yizhiyanhua-ai/media-downloader, 403 stars), Youtube Thumbnail (hassancs91/claude-youtube-editor, 328 stars) and Shorts Video Maker (uxjoseph/content-marketing-team, 107 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Youtube Thumbnail?

magnus919 (a GitHub user) maintains it in magnus919/agent-skills, which has 115 GitHub stars. The repository holds 131 skills in this directory. The repository was last updated on October 10, 2026.

Source: magnus919/agent-skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.