Thumbnail Skill
This skill enables generation of high-performing thumbnails and cover images optimized for click-through rate (CTR). Thumbnails are designed to spark curiosity, complement titles, and compel viewers to click.
Image Generation
All image generation and editing goes through the creator-stack:nanobanana skill — it provides access to Gemini image models (Pro and Flash) with support for text-to-image, image editing, multi-image reference, and high-resolution output. Invoke it before generating or editing any thumbnail.
Model Selection for Thumbnails
- Pro (default) — Use for final production thumbnails. Supports 2K/4K resolution, up to 14 reference images, and thinking mode for better composition.
- Flash — Use for rapid exploration and draft concepts. Faster and cheaper, good for iterating on ideas before committing to a final version.
Rule of thumb: Use Flash for exploration batches (generate 5-10 variations), then Pro for the final production image.
Essential References
Read both of these before generating any thumbnail — they contain the design patterns and prompting techniques that make the difference between a generic image and a high-CTR thumbnail:
references/thumbnail-formulas.md— Design formulas for high CTR thumbnails through proven strategies. These principles apply universally across platforms.references/prompting-guidelines.md— Thumbnails are generated using Gemini image models (NanoBanana). The prompting guidelines help you get more predictable and consistent results.
Skipping these leads to generic thumbnails that don't follow proven patterns — always load them first.
Platform Context
When invoked by orchestrator skills, platform-specific context (dimensions, safe zones, format requirements) may be provided. Use the provided context to set the correct output dimensions and constraints.
Default dimensions: When no platform context is given, default to YouTube thumbnail dimensions (1280x720, 16:9 aspect ratio).
Common platform dimensions:
- YouTube thumbnail: 1280x720 (16:9)
- Blog feature image: 1200x630
- Course thumbnail: 1280x720 or 1080x1080
- Newsletter header: 1100x220 or 1200x630
- Social media card: 1200x675
Always confirm the target platform before generating to ensure correct dimensions.
Reference Images
With both generating and editing thumbnails, you can include reference images. Examples include but are not limited to thumbnail templates, headshots, icons, logos, or images for style transfer. See the Prompting Guidelines above for more.
All reference images MUST be passed using absolute paths.
Using Official Logos
If using company logos, use actual images by passing the absolute path to the image files instead of simply describing them. Nanobanana does not know what common company logos look like.
If a company logo is not locally available, you can search for it online and download it using curl, then pass the absolute path to the downloaded image in the prompt. Save all downloaded images to ./downloads/, making the directory if it does not exist.
Common Mistakes to Avoid
WRONG: "create the Claude AI logo (an orange C shape)" CORRECT: Pass the actual logo file as a reference image
WRONG: "add the Python logo" CORRECT: Use /absolute/path/to/python-logo.png as a reference image
Proven Designs
If you know the content title or subject, search for related OUTLIER content. Focus on OUTLIERS because they are already proven to work well and very likely have high click-through rates. Videos are outliers if they have a high amount of views compared to the subscriber count of the channel. For example, if a video has 10,000+ views from a channel with less than 5,000 subscribers, that video is an outlier.
Once you have a list of outlier videos, you can access their thumbnails and use them to style transfer.
Here is a URL example of a standard definition thumbnail for a video with id "rmvDxxNubIg": https://img.youtube.com/vi/rmvDxxNubIg/sddefault.jpg. You can download the image using curl to ./downloads/outliers/, and then read the image file to understand it. Use it as a reference image when using for style transfer.
Brand Compliance
When creating visual assets for The AI Launchpad, invoke creator-stack:brand-guidelines to resolve the correct design system and check anti-patterns. This ensures all thumbnails are consistent with the established brand identity, color palette, and visual style.
For other brands, check if a brand guidelines skill exists at ~/.claude/skills/ and apply any relevant design constraints.
Workflows
Generating Thumbnail Concepts
Once you have generated an initial thumbnail concept or prompt, use the Thumbnail Reviewer agent to review the concept and provide feedback. The reviewer will provide a critique and suggest improvements. Consider the reviewer's feedback and incorporate it before proceeding. Limit the generate-review-regenerate loop to a single pass — additional iterations yield diminishing returns and the reviewer's first critique captures the most impactful changes.
Optimizing Thumbnails
Because creator-stack:nanobanana supports image editing, you can iteratively modify and improve a previously generated thumbnail. Pass the original thumbnail as a reference image and describe the desired changes.
Always review generated thumbnails to ensure they meet the complete design formulas and original intent. If not, you can iterate by editing the original thumbnail. Limit the generate-review-regenerate loop to a single pass — additional iterations yield diminishing returns and the reviewer's first critique captures the most impactful changes.
User Assets
If the user has specified any local assets (e.g. thumbnail templates, headshots, icons, logos, etc.) in their local context, bias towards incorporating them into the thumbnail when relevant. For example, thumbnails with actual people in them have been shown to perform better.