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DenialGelon

nano-banana-mcp

by DenialGelon
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nano-banana-mcp

A minimal MCP server that wraps Google Gemini image generation ("Nano Banana") for use inside Claude Code or any other MCP-compatible host.

Built as part of an exploration of agentic workflows for K-12 teaching materials. The whole server is about 75 lines of Python — readable in one sitting.

What it does

Exposes a single tool:

generate_image(prompt: str, output_path: str, model: str | None = None) -> str

  • Writes a PNG to output_path

  • Auto-suffixes on collision (foo.png → foo-1.png, foo-2.png, …) — never silently overwrites

  • Returns the absolute path it actually wrote to

Related MCP server: Gemini Image Generation MCP

Install on a new machine

You need:

brew install pipx
pipx ensurepath
pipx install git+https://github.com/DenialGelon/nano-banana-mcp

claude mcp add nano-banana --scope user \
  --env GEMINI_API_KEY=<your-key> -- nano-banana-mcp

Verify with claude mcp list — you should see nano-banana: ✓ Connected.

Use

Start a fresh Claude Code session and ask:

Generate an image of a friendly cartoon banana mascot and save it to ~/Desktop/banana.png

Claude will pick up the tool and call it. The return value tells you the final path (with a note if a collision was auto-resolved).

Models

The model argument is optional. Known values (verified 2026-05-18 at the Gemini image-generation docs):

Model string

Nickname

Use for

gemini-2.5-flash-image (default)

Nano Banana

Fast / cheap drafts

gemini-3.1-flash-image-preview

Nano Banana 2

Higher quality, balanced

gemini-3-pro-image-preview

Nano Banana Pro

Top quality, costliest

Update / rotate the key

Update the code:

pipx install --force git+https://github.com/DenialGelon/nano-banana-mcp

Rotate the API key:

claude mcp remove nano-banana --scope user
claude mcp add nano-banana --scope user \
  --env GEMINI_API_KEY=<new-key> -- nano-banana-mcp

License

MIT — see LICENSE.

Available Tools

1 tool
generate_imageA

Generate an image with Gemini and save it to output_path.

Known model values (override via model):

  • gemini-2.5-flash-image (default — Nano Banana, fastest/cheapest)

  • gemini-3.1-flash-image-preview (Nano Banana 2, higher quality)

  • gemini-3-pro-image-preview (Nano Banana Pro, top quality)

If output_path already exists, a numeric suffix is appended (foo.png -> foo-1.png) and the final path is returned.

ParametersJSON Schema
NameRequiredDescriptionDefault
promptYes
output_pathYes
modelNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.2/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Discloses the non-overwriting behavior (appending numeric suffix) and indicates that the final path is returned. With no annotations, this is above average transparency, though lacks detail on failure handling or authorization.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Economical two-sentence structure: first sentence gives the main action, then bullet-style model list and a clear conflict rule. No filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool has an output schema (which documents return structure) and only three parameters, the description covers model selection and file conflict behavior. Missing details on error handling or input format, but sufficient for basic usage.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Adds meaning to the 'model' parameter by listing known values and their trade-offs, but 'prompt' and 'output_path' receive no extra description beyond their names. Schema coverage is 0%, so description partially compensates.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Clearly states the action ('generate an image') and the destination ('save to output_path'), with specific reference to Gemini. No siblings exist, so differentiation is not needed.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit model variants with nicknames and quality/cost tiers, plus conflict resolution behavior when output path exists. No exclusions or alternatives needed due to no siblings.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. 1 tool updatev0.1.0
    • First observedgenerate_image
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TDQS

A4.1/5.0
Disambiguation5/5

Only one tool exists, so there is no possibility of confusion between tools.

Naming Consistency5/5

The single tool name 'generate_image' follows a clear verb_noun pattern, consistent with common conventions.

Tool Count3/5

With only one tool, the server feels thin for its apparent scope (image generation), but it covers the primary action without unnecessary bloat.

Completeness3/5

The tool covers the core generation task, but lacks additional operations such as listing models, managing outputs, or deleting images, leaving minor gaps for an agent.

Maintenance

ActivityInactive
ResponsivenessNo issues

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