Video Thumbnail Generator Agent Skill
Create platform-ready thumbnails from real video frames. Use when the user wants a thumbnail, cover image, YouTube cover, Shorts cover, Bilibili cover, Xiaohongshu cover, or other video poster image.
Install
one command, takes just this skill from the repositorynpx skills add https://github.com/0xsline/OpenChatCut --skill video-thumbnail-generatorThe instruction itself
5 sections, as written by the authorVideo Thumbnail Generator
Use this skill to create a high-clarity thumbnail or cover image from the actual video content.
Non-Negotiables
- Use the real video as visual evidence.
- If the thumbnail shows a person, product, UI, frame, or scene from the video, extract or inspect real frames.
- Never invent a generic software interface, fake product screen, or unrelated person.
- Read style references before recommending styles.
- Use
references/thumbnail-styles.mdandreferences/thumbnail-style-recipes.md. - Only offer style directions supported by those references or by the user's explicit instruction.
- Keep text short and readable.
- Usually 2-5 words.
- Avoid thin type, low contrast, small labels, and clutter.
Workflow
- Confirm platform and aspect ratio if missing.
- YouTube / Bilibili: usually 16:9.
- Shorts / TikTok / Douyin: usually 9:16.
- Xiaohongshu / WeChat Channels: usually 3:4.
- Correct ambiguous ratio language gently, especially 4:3 vs 3:4.
- Read project state, transcript, and available media context.
- Inspect candidate frames:
- expressive face
- product or UI clearly visible
- dramatic action moment
- clean composition
- strong lighting or clear subject separation
- Classify the thumbnail job:
- talking-head / opinion / tutorial
- product / software / demo
- cinematic / documentary / art
- entertainment / challenge / reaction
- education / business / concept
- Propose concise title text options.
- Offer 3-6 clearly different style directions.
- Each option should name the composition, not only a channel/style label.
- Exclude weak options.
- Wait for user choice when the direction is not obvious.
- Generate thumbnail options using selected real frames and the selected style.
- Check mobile readability, subject fidelity, product/UI truthfulness, and visual contrast.
- Present results and offer targeted adjustments.
Prompt Shape
[Platform] thumbnail, [aspect ratio / dimensions], [style name].
COMPOSITION: [subject position, scale, background, graphic balance]
REAL REFERENCE: [describe selected frame zone by zone]
TEXT: "[short title]" in [high-contrast style]
STYLE: [one-line style recipe from references]
CONSTRAINTS: readable at mobile size, no fake UI, no watermark, no play button.
References
references/thumbnail-styles.md: style library from real thumbnail analysis.references/thumbnail-style-recipes.md: quick style recipes and prompt patterns.references/field-testing-notes.md: known failure modes.
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How to use it
Take 0xsline/video-thumbnail-generator from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.