Image Gen

Image Generation Gateway

Acceptable use. Hosted-instance traffic is governed by the Terms of Service — including a generative-content acceptable-use policy — and by the upstream model providers' usage policies. Wallets used for prohibited content are blocked before settlement. Outputs are generated by third-party models from your inputs; you are responsible for how you use them.

Three tiers of text-to-image generation, paywalled via x402. An agent sends a prompt and pays per call with USDC on Base, Solana, Polygon, Arbitrum, Monad, Celo, Stellar, or Algorand -- no OpenAI API key needed on the caller's side, no signup, no account. The operator's own OPENAI_API_KEY handles upstream auth; per-tier prompt caps and locked quality/size settings keep worst-case upstream cost well below the x402 price.

Tiers

Endpoint	Price	Model	Quality	Size	Prompt cap
POST /api/image-gen	$0.03	gpt-image-1-mini	low	1024x1024	1,000 chars
POST /api/image-gen-hd	$0.10	gpt-image-1-mini	medium	1024x1024	2,000 chars
POST /api/image-gen-premium	$0.30	gpt-image-2	medium	1024x1024	4,000 chars

All three tiers are wallet-only -- there is no proof-of-work free tier because every call burns real upstream inference credit. See Security Model for the wallet-only rationale.

Request format

Every tier accepts the same JSON body:

{
  "prompt": "A photorealistic red apple on a white background, studio lighting"
}

Field	Required	Notes
prompt	yes	Text description of the desired image; max length varies by tier

Response format

Every tier returns the same envelope:

{
  "model": "gpt-image-1-mini",
  "provider": "openai",
  "quality": "low",
  "size": "1024x1024",
  "image": "<base64-encoded PNG>",
  "revised_prompt": "A photorealistic red apple on a white background, studio lighting"
}

Field	Description
model	The model that generated the image
provider	Always openai
quality	The quality setting used (low or medium)
size	The image dimensions
image	Base64-encoded PNG image data
revised_prompt	The prompt as interpreted by the model (may differ from input)

Curl examples

Standard tier ($0.03 -- GPT Image mini, low quality)

curl -X POST https://agent402.tools/api/image-gen \
  -H 'Content-Type: application/json' \
  -d '{
    "prompt": "A single red apple on a white background"
  }'

HD tier ($0.10 -- GPT Image mini, medium quality)

curl -X POST https://agent402.tools/api/image-gen-hd \
  -H 'Content-Type: application/json' \
  -d '{
    "prompt": "A detailed watercolor painting of a mountain village at sunset"
  }'

Premium tier ($0.30 -- GPT Image 2, medium quality)

curl -X POST https://agent402.tools/api/image-gen-premium \
  -H 'Content-Type: application/json' \
  -d '{
    "prompt": "An isometric 3D render of a futuristic city block with neon signs and flying cars, cyberpunk aesthetic"
  }'

All three return 402 without a valid x402 payment header -- the same flow as every other paid tool. See Paying with x402 for how to sign and attach payment.

Operator caps that protect margins

The per-tier caps are set so that the worst-case upstream OpenAI cost stays comfortably below the x402 price charged to the caller:

• Prompt cap (chars) limits how much text the caller can send, bounding input-token cost.
• Quality lock per tier prevents a caller from requesting higher quality than the tier's price covers.
• Size lock (1024x1024) prevents a caller from requesting larger images that cost more upstream.
• Model lock per tier prevents a caller from requesting a more expensive model than the tier covers.

These caps are enforced server-side before the upstream call is made -- a misconfigured client cannot cause the operator to lose money.

Environment gating

The kit reads OPENAI_API_KEY at call time, not at boot. If the key is missing or empty, calls return 503 Service Unavailable and the rest of the server continues running normally. Self-hosters who don't want to offer image generation simply omit the env var -- no code change needed.

See also

• LLM Proxy Gateway -- the text inference proxy (same pattern, different modality)
• Paying with x402 -- the USDC payment flow these endpoints require
• Security Model -- why these tools are wallet-only (no PoW free tier)
• API Reference -- full HTTP endpoint reference
• Tool Catalog -- where these three tools sit in the catalog