bfl-api

SKILL.md

BFL API Integration Guide

Use this skill when integrating BFL FLUX APIs into applications for image generation, editing, and processing.

First: Check API Key

Before generating images, verify your API key is set:

echo $BFL_API_KEY

If empty or you see "Not authenticated" errors, see API Key Setup below.

Important: Image URLs Expire in 10 Minutes

Result URLs from the API are temporary. Download images immediately after generation completes - do not store or cache the URLs themselves.

When to Use

Setting up BFL API client

Implementing async polling patterns

Handling rate limits and errors

Configuring webhooks for production

Selecting regional endpoints

Building production-ready integrations

Quick Reference

Base Endpoints

Region
Endpoint
Use Case

Global
https://api.bfl.ai
Default, automatic failover

EU
https://api.eu.bfl.ai
GDPR compliance

US
https://api.us.bfl.ai
US data residency

Model Endpoints & Pricing

Credit pricing: 1 credit = $0.01 USD. FLUX.2 uses megapixel-based pricing (cost scales with resolution).

FLUX.2 Models

Model
Path
1st MP
+MP
1MP T2I
1MP I2I
Best For

FLUX.2 [klein] 4B
/v1/flux-2-klein-4b
1.4c
0.1c
$0.014
$0.015
Real-time, high volume

FLUX.2 [klein] 9B
/v1/flux-2-klein-9b
1.5c
0.2c
$0.015
$0.017
Balanced quality/speed

FLUX.2 [pro]
/v1/flux-2-pro
3c
1.5c
$0.03
$0.045
Production, fast turnaround

FLUX.2 [max]
/v1/flux-2-max
7c
3c
$0.07
$0.10
Maximum quality

FLUX.2 [flex]
/v1/flux-2-flex
5c
5c
$0.05
$0.10
Typography, adjustable controls

FLUX.2 [dev]
-
-
-
Free
Free
Local development (non-commercial)

Pricing formula: (firstMP + (outputMP-1) * mpPrice) + (inputMP * mpPrice) in cents

FLUX.1 Models

Model
Path
Price/Image
Best For

FLUX.1 Kontext [pro]
/v1/flux-kontext
$0.04
Image editing with context

FLUX.1 Kontext [max]
/v1/flux-kontext-max
$0.08
Max quality editing

FLUX1.1 [pro]
/v1/flux-pro-1.1
$0.04
Standard T2I, fast & reliable

FLUX1.1 [pro] Ultra
/v1/flux-pro-1.1-ultra
$0.06
Ultra high-resolution

FLUX1.1 [pro] Raw
/v1/flux-pro-1.1-raw
$0.06
Candid photography feel

FLUX.1 Fill [pro]
/v1/flux-pro-1.0-fill
$0.05
Inpainting

Tip: All FLUX.2 models support image editing via the input_image parameter - no separate editing endpoint needed. Use bfl.ai/pricing calculator for exact costs at different resolutions.

Image Input for Editing

Preferred: Use URLs directly - simpler and more convenient than base64.

Single image editing:

curl -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "Change the background to a sunset",
    "input_image": "https://example.com/photo.jpg"
  }'

Multi-reference editing:

curl -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "The person from image 1 in the environment from image 2",
    "input_image": "https://example.com/person.jpg",
    "input_image_2": "https://example.com/background.jpg"
  }'

The API fetches URLs automatically. Both URL and base64 work, but URLs are recommended when available.

Multi-Reference I2I

FLUX.2 models support multiple input images for combining elements, style transfer, and character consistency:

Model
Max References

FLUX.2 [klein]
4 images

FLUX.2 [pro/max/flex]
8 images

Parameters: input_image, input_image_2, input_image_3, ... input_image_8

Prompt pattern: Reference images by number in your prompt:

"The subject from image 1 in the environment from image 2"

"Apply the style of image 2 to the scene in image 1"

"The person from image 1 wearing the outfit from image 2, in the pose from image 3"

For detailed multi-reference patterns (character consistency, style transfer, pose guidance), see flux-best-practices/rules/multi-reference-editing.md

Rate Limits

Tier
Concurrent Requests

Standard (most endpoints)
24

Polling vs Webhooks

Approach
Use When

Polling
Scripts, CLI tools, local development, single requests, simple integrations

Webhooks
Production apps, high volume, server-to-server, when you need immediate notification

Start with polling - it's simpler and works everywhere. Switch to webhooks when you need to scale or want event-driven architecture.

Key Behaviors

Polling: Response includes polling_url for async results

URL Expiration: Result URLs expire after 10 minutes

Webhook Support: Configure webhook_url for production workloads

API Key Setup

Required: The BFL_API_KEY environment variable must be set before using the API.

Quick Check

echo $BFL_API_KEY

If Not Set

Get a key: Go to https://dashboard.bfl.ai/get-started → Click "Create Key" → Select organization

Save to .env (recommended for persistence):
echo 'BFL_API_KEY=bfl_your_key_here' >> .env
echo '.env' >> .gitignore  # Don't commit secrets

See references/api-key-setup.md for detailed setup instructions.

Authentication

x-key: YOUR_API_KEY

Basic Request Flow

1. POST request to model endpoint
   └─> Response: { "polling_url": "..." }

2. GET polling_url (repeat until complete)
   └─> Response: { "status": "Pending" | "Ready" | "Error", ... }

3. When Ready, download result URL
   └─> URL expires in 10 minutes - download immediately

Related

Prompting best practices (T2I, I2I, typography, colors): see the flux-best-practices skill

Multi-reference patterns (character consistency, style transfer, pose guidance): see flux-best-practices/rules/multi-reference-editing.md

References

references/api-key-setup.md - API key creation and configuration

references/endpoints.md - Complete endpoint documentation

references/polling-patterns.md - Async polling implementation

references/rate-limiting.md - Rate limit handling strategies

references/error-handling.md - Error codes and recovery

references/webhook-integration.md - Webhook setup and security

Code Examples

Note: cURL examples are preferred by default as they work universally without requiring Python or Node.js. Use language-specific clients when building production applications.

references/code-examples/curl-examples.sh - cURL examples (recommended)

references/code-examples/python-client.py - Python client

references/code-examples/typescript-client.ts - TypeScript client

Quick Start Example

1. Submit Generation Request

curl -s -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A serene mountain landscape at sunset", "width": 1024, "height": 1024}'

Response:

{ "id": "abc123", "polling_url": "https://api.bfl.ai/v1/get_result?id=abc123" }

2. Poll for Result

curl -s "POLLING_URL" -H "x-key: $BFL_API_KEY"

Response when ready:

{ "status": "Ready", "result": { "sample": "https://...", "seed": 1234 } }

3. Download Image

curl -s -o output.png "IMAGE_URL"

Tip: Result URLs expire in 10 minutes. Download immediately after status becomes Ready.

4. Multi-Reference Example

Combine elements from multiple images:

curl -s -X POST "https://api.bfl.ai/v1/flux-2-pro" \
  -H "x-key: $BFL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "The cat from image 1 sitting in the cozy room from image 2",
    "input_image": "https://example.com/cat.jpg",
    "input_image_2": "https://example.com/room.jpg",
    "width": 1024,
    "height": 1024
  }'

Reference images by number in your prompt. See Multi-Reference I2I for limits and patterns.