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

> Source: <https://github.com/DexterLagan/NanoUI>
> Published: 2026-09-03 09:24:14+00:00

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