banana-youtube

A tool for creating YouTube thumbnail images, which are the preview pictures shown for videos. It uses Gemini to make high-contrast compositions with dramatic expressions and framing.

In plain words
What is it for?
Use it to generate thumbnail concepts from a video topic or description, then save the resulting image for a YouTube video.
Why use it?
It gives video creators a defined process for turning a topic into a thumbnail brief and an image. It also sets the required image format and quality for thumbnails.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/agentic-dev3o/devx-plugins/banana-youtube
Any agent
npx skills add agentic-dev3o/devx-plugins --skill banana-youtube
Clone the repo
git clone --depth 1 https://github.com/agentic-dev3o/devx-plugins

Made for: Claude Code, Codex.

Per session 54 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,376 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00054 $0.01376
Opus 5 $0.00027 $0.00688
Sonnet 5 $0.00011 $0.00275
Haiku 4.5 $0.00005 $0.00138

Measured 2d ago against content hash b9be80e53f6b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

banana-youtube 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 2d 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.

plugins/nano-banana-ultimate/skills/banana-youtube/SKILL.md · 112 lines

How it starts

The opening of the file, as written. The whole thing — 112 lines — stays where its author put it; the contents beside it link to each section on GitHub.

YouTube Thumbnail Maker

Input: $ARGUMENTS (optional — video topic or thumbnail description)

If $ARGUMENTS is provided, use it as the video topic and skip to prompt building. If empty, ask what the video is about.

Requirements

Workflow

  1. Understand — Parse the user's request. Identify the video topic, target emotion, and channel style. If the subject or intent is unclear, ask ONE clarifying question.
  2. Build prompt — Construct a detailed Gemini prompt using the Prompt Formula below. Prioritize dramatic facial expressions, bold colors, and high visual contrast.
  3. Configure — ALWAYS use 16:9, 2K, and the Pro model. These are non-negotiable for thumbnails.
  4. Generate — Run the script.
  5. Deliver — Report the saved file path. Do NOT read the image file back. Offer to iterate: adjust expression, background color, composition, or prompt.

Prompt Formula

Build every thumbnail prompt using this structure:

[Subject with Expression] + [Dramatic Reaction/Gesture] + [Bold Colored Background] + [Close-Up Rule-of-Thirds] + [Hyper-Saturated Photography with Rim Lighting]

Rules

  • Positive framing: Describe what IS in the image, never what is absent.
  • Strong verb opener: Start with Generate, Create, Capture, Render, Design, Compose.
  • Faces sell clicks: Always include a face with an exaggerated expression — wide eyes, open mouth, raised eyebrows, shocked grin.
  • Bold backgrounds: Use solid, saturated colors (electric blue, hot pink, neon green, deep orange) or dramatic gradients.
  • Rim lighting: Add a strong backlight or rim light to separate the subject from the background and create a cinematic pop.
  • Text space: Reserve approximately one-third of the frame for text overlay — typically the opposite side from the subject.
  • No celebrity likenesses: Never reference real public figures. Describe features generically.

Read the full file on GitHub · 112 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

  1. 2d ago First seen · 112 lines · 54 tokens per session scan A b9be80e53f6b

Subscribe to this mod's changes

banana-youtube is a skill published in the GitHub repository agentic-dev3o/devx-plugins (11 stars, last pushed 14d ago), licensed MIT. It adds 54 tokens to every session and 1,376 once invoked, about $0.0003 per session on Opus 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 2026-08-30.

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