nanobot/docs/image-generation.md

Image Generation

nanobot can generate and edit images through the generate_image tool. In the WebUI, users can enable Image Generation from the composer, choose an aspect ratio, and keep iterating on generated images inside the same chat.

The feature is disabled by default. Enable it in ~/.nanobot/config.json, configure a supported image provider, then restart the gateway.

Quick Setup

{
  "providers": {
    "openrouter": {
      "apiKey": "${OPENROUTER_API_KEY}"
    }
  },
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "openrouter",
      "model": "openai/gpt-5.4-image-2"
    }
  }
}

See Provider Notes for AIHubMix, MiniMax, and Gemini configuration examples.

Tip

Prefer environment variables for API keys. nanobot resolves ${VAR_NAME} values from the environment at startup.

WebUI Usage

In the WebUI composer:

1. Click Image Generation.
2. Choose an aspect ratio: Auto, 1:1, 3:4, 9:16, 4:3, or 16:9.
3. Describe the image or the edit you want.
4. Attach reference images when editing an existing image.

Generated images are rendered as assistant media in the chat. Follow-up prompts such as "make it warmer", "change the background", or "try a 16:9 version" can reuse the most recent generated artifact.

The WebUI hides provider storage details from the user. The agent sees the saved artifact path internally and can pass it back to generate_image as reference_images for iterative edits.

Configuration Reference

Option	Type	Default	Description
tools.imageGeneration.enabled	boolean	false	Register the generate_image tool
tools.imageGeneration.provider	string	"openrouter"	Image provider name. Supported values: openrouter, aihubmix, minimax, gemini, stepfun
tools.imageGeneration.model	string	"openai/gpt-5.4-image-2"	Provider model name
tools.imageGeneration.defaultAspectRatio	string	"1:1"	Default ratio when the prompt/tool call does not specify one
tools.imageGeneration.defaultImageSize	string	"1K"	Default size hint, for example 1K, 2K, 4K, or 1024x1024
tools.imageGeneration.maxImagesPerTurn	number	4	Maximum count accepted by one tool call. Valid range: 1 to 8
tools.imageGeneration.saveDir	string	"generated"	Relative directory under nanobot's media directory for generated artifacts

Provider settings reuse normal provider config fields:

Option	Description
providers.<name>.apiKey	Provider API key. Prefer ${ENV_VAR}
providers.<name>.apiBase	Optional custom base URL
providers.<name>.extraHeaders	Headers merged into provider requests
providers.<name>.extraBody	Extra JSON fields merged into provider request bodies

Both camelCase and snake_case config keys are accepted, but docs use camelCase to match config.json.

Provider Notes

OpenRouter

OpenRouter uses a chat-completions style image response. Configure:

{
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "openrouter",
      "model": "openai/gpt-5.4-image-2"
    }
  }
}

Use a model that supports image generation and image editing if you want reference-image edits.

AIHubMix

AIHubMix gpt-image-2-free is supported through AIHubMix's unified predictions API. Internally nanobot calls:

/v1/models/openai/gpt-image-2-free/predictions

Configure:

{
  "providers": {
    "aihubmix": {
      "apiKey": "${AIHUBMIX_API_KEY}",
      "extraBody": {
        "quality": "low"
      }
    }
  },
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "aihubmix",
      "model": "gpt-image-2-free"
    }
  }
}

quality: low is optional. It can make free image models faster and less likely to time out, but it is not required for correctness.

MiniMax

MiniMax image-01 supports text-to-image and reference-image (subject reference) edits. Supported aspect ratios are 1:1, 16:9, 4:3, 3:2, 2:3, 3:4, 9:16, and 21:9.

{
  "providers": {
    "minimax": {
      "apiKey": "${MINIMAX_API_KEY}"
    }
  },
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "minimax",
      "model": "image-01",
      "defaultAspectRatio": "1:1"
    }
  }
}

Gemini

nanobot supports two Gemini image generation model families via Google's Generative Language API:

Model	Endpoint	Reference images
imagen-4.0-generate-001	:predict	Not supported by this integration
gemini-2.5-flash-image	:generateContent	Supported

For reference-image edits, use a Gemini Flash image model:

{
  "providers": {
    "gemini": {
      "apiKey": "${GEMINI_API_KEY}"
    }
  },
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "gemini",
      "model": "gemini-2.5-flash-image"
    }
  }
}

Imagen 4 supports the aspect ratios 1:1, 9:16, 16:9, 3:4, and 4:3. Unsupported ratios are ignored and the model uses its default. The defaultImageSize setting has no effect on Gemini models; sizing is controlled by defaultAspectRatio only. Reference images passed with an Imagen model are ignored (with a warning logged).

StepFun

StepFun (阶跃星辰) step-image-edit-2 supports text-to-image generation. The step-1x-medium variant additionally supports style-reference image edits, where a reference image guides the visual style of the output.

Supported aspect ratios: 1:1, 16:9, 9:16, 3:4, 4:3. Sizes are specified as WIDTHxHEIGHT (e.g. 1024x1024, 1280x800, 800x1280).

{
  "providers": {
    "stepfun": {
      "apiKey": "${STEPFUN_API_KEY}"
    }
  },
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "stepfun",
      "model": "step-image-edit-2"
    }
  }
}

Note

The StepFun provider reuses the existing providers.stepfun config block (the same one used for StepFun's LLM API). Set providers.stepfun.apiKey once and it is shared between text and image generation.

When step-image-edit-2 is used, reference_images are ignored (the model does not support style reference). Switch to step-1x-medium to use reference-image-guided generation.

StepPlan (Subscription)

StepPlan is StepFun's subscription tier and uses a different API base URL. The image generation endpoint path is the same — just override apiBase:

{
  "providers": {
    "stepfun": {
      "apiKey": "${STEPFUN_API_KEY}",
      "apiBase": "https://api.stepfun.com/step_plan/v1"
    }
  },
  "tools": {
    "imageGeneration": {
      "enabled": true,
      "provider": "stepfun",
      "model": "step-image-edit-2"
    }
  }
}

apiBase takes precedence over the registry default, so with the StepPlan base URL configured, image requests are sent to https://api.stepfun.com/step_plan/v1/images/generations — the same path prefix used for LLM calls. The API key is shared with the standard StepFun provider.

Artifacts

Generated images are stored under the active nanobot instance's media directory:

~/.nanobot/media/generated/YYYY-MM-DD/img_<id>.<ext>
~/.nanobot/media/generated/YYYY-MM-DD/img_<id>.json

For non-default config locations, the media directory is relative to the active config file's directory.

The JSON sidecar stores:

Field	Meaning
id	Short generated image id, such as img_ab12cd34ef56
path	Local image path used internally for follow-up edits
mime	Detected image MIME type
prompt	Prompt used for the generation
model	Provider model
provider	Provider name
source_images	Reference image paths used for edits
created_at	Creation timestamp

Do not paste base64 image payloads into chat. The agent should keep local artifact paths internal unless the user explicitly asks for debugging details.

Prompting

Good image prompts include:

• Subject and scene.
• Composition, camera, or layout.
• Style, mood, lighting, and color palette.
• Exact text that must appear in the image, quoted.
• Constraints such as "keep the same character" or "preserve the logo".

Example:

A minimal app icon for nanobot: friendly robot head, rounded square, soft blue and white palette, clean vector style, no text

For edits, describe what should change and what must stay fixed:

Use the reference image. Keep the same robot and composition, change the palette to warm orange, and add a subtle sunrise background.

Troubleshooting

Symptom	Check
generate_image is not available	Set tools.imageGeneration.enabled to true and restart the gateway
Missing API key error	Configure providers.<provider>.apiKey; if using ${VAR_NAME}, confirm the environment variable is visible to the gateway process
unsupported image generation provider	Use openrouter, aihubmix, minimax, gemini, or stepfun
AIHubMix says Incorrect model ID	Use model: "gpt-image-2-free"; nanobot expands it to the required openai/gpt-image-2-free model path internally
Generation times out	Try a smaller/default image size, set AIHubMix extraBody.quality to "low", or retry later
Reference image rejected	Reference image paths must be inside the workspace or nanobot media directory and must be valid image files