Show HN: NanoUI – A small native macOS app for generating images with OpenRouter

Dexter Lagan released NanoUI, a free, open-source native macOS app for Apple Silicon that generates images via OpenRouter's Image API, supporting 16 models including Nano Banana 2, GPT Image 2, and FLUX.2 Pro. The SwiftUI app offers per-model resolution, aspect ratio, quality controls, reference-image uploads (up to 14 for Nano Banana 2), multi-image generation (up to 10), and 1:1 zoom, with an unsigned build available on GitHub.

A small native macOS app Apple Silicon for generating images with OpenRouter's Image API https://openrouter.ai/docs/features/multimodal/image-generation . Written in SwiftUI, no external dependencies. 16 image models — Nano Banana 1 / 2 / Pro / Lite, GPT Image 1 / 2, GPT-5 Image, GPT-5.4 Image 2, FLUX.2 Pro, Seedream 4.5, Grok Imagine 2.0, Qwen Image 3, Recraft V4, Riverflow V2.5 Pro, MAI Image 2.5 Pro, Krea 2 Large Per-model controls — resolution 512 – 4K , aspect ratio, and quality pickers appear only when the selected model supports them Reference images — image-to-image editing with a per-model upload cap up to 14 for Nano Banana 2 ; thumbnails with one-click removal Multi-image generation — n stepper for models that support it up to 10 Zoom toggle — results are fitted to the window by default; click an image to switch to 1:1 pixel zoom scrollable , click again to fit back Save as… — per-image save panel with the correct file extension API key — read from OPENROUTER API KEY when set; otherwise a key can be pasted in-app and optionally saved with Remember on this Mac stored in plaintext under ~/Library/Preferences/local.nanoui.app.plist ; unchecking the toggle deletes it Download the latest NanoUI-macos-arm64.zip from Releases https://github.com/DexterLagan/NanoUI/releases , unzip, and drag NanoUI.app to your Applications folder. The build is unsigned — on first launch, right-click the app in Finder and choose Open , then confirm. Launching it from the terminal also works: OPENROUTER API KEY=sk-or-... open /Applications/NanoUI.app - Pick a model from the dropdown defaults to Nano Banana 2 . - Optionally set resolution, aspect ratio, and quality for the selected model. - Click Add to upload up to 14 reference images the counter shows the model's limit . - Type a prompt and hit Generate . - Click the result to toggle between fit-to-window and 1:1 zoom. Use Save Image… to export. Requirements: macOS 14+, Xcode Command Line Tools xcode-select --install , Apple Silicon. Run directly debug build, opens a window swift run Build a double-clickable NanoUI.app release ./build-app.sh The app targets the dedicated Image API POST /api/v1/images . Parameters used: model , prompt , n , resolution , aspect ratio , quality , and input references base64 data URLs . Per-model capabilities allowed resolution/aspect values, reference limits, max n are hardcoded in Sources/NanoUI/OpenRouterService.swift from OpenRouter's Image Models API https://openrouter.ai/api/v1/images/models discovery data. | Model | Resolution | Max refs | Max n | Quality | |---|---|---|---|---| Nano Banana 2 google/gemini-3.1-flash-image | 512, 1K, 2K, 4K | 14 | 1 | — | Nano Banana google/gemini-2.5-flash-image | — | 3 | 1 | — | Nano Banana Pro google/gemini-3-pro-image | 1K, 2K, 4K | 14 | 1 | — | | Gemini 3.1 Flash Lite Image | 1K | 14 | 1 | — | GPT Image 2 openai/gpt-image-2 | — | 16 | 10 | auto/low/medium/high | | GPT Image 1 | — | 16 | 10 | auto/low/medium/high | | GPT-5 Image | — | 16 | 10 | auto/low/medium/high | | GPT-5.4 Image 2 | — | 16 | 10 | auto/low/medium/high | | FLUX.2 Pro | — | 8 | 1 | — | | Seedream 4.5 | 1K, 2K, 4K | 14 | 10 | — | | Grok Imagine 2.0 | 1K, 2K | 3 | 1 | low/medium | | Qwen Image 3 | 1K, 2K | 4 | 6 | — | | Recraft V4 | — | 1 | 6 | — | | Riverflow V2.5 Pro | 1K, 2K, 4K | 10 | 1 | — | | MAI Image 2.5 Pro | — | 1 | 1 | — | | Krea 2 Large | 1K | 1 | 1 | — | Full parameter set for the default model, per OpenRouter's discovery API: resolution : 512 , 1K , 2K , 4K aspect ratio : 1:1 , 1:4 , 1:8 , 2:3 , 3:2 , 3:4 , 4:1 , 4:3 , 4:5 , 5:4 , 8:1 , 9:16 , 16:9 , 21:9 input references : 0–14 images n : 1 seed : boolean not exposed in the UI Package.swift Swift package definition Sources/NanoUI/NanoUIApp.swift App entry point Sources/NanoUI/ContentView.swift UI: model picker, references, prompt, results Sources/NanoUI/OpenRouterService.swift Image API client + model catalog build-app.sh Builds the release .app bundle icon.svg App icon source vector icon-512x512.png / Icon.icns App icon raster and macOS icon bundle MIT /DexterLagan/NanoUI/blob/main/LICENSE © 2026 Dexter Santucci