Flux CLI (BFL / FLUX)

CLI to generate and edit images via the BFL FLUX API.

Quick start

1. API key:

• env:
  • export BFL_API_KEY="..."
• or save locally (reads from stdin; avoid shell history leaks):
  • echo "$BFL_API_KEY" | flux config set apiKey

2. Generate:

• flux gen "a cat astronaut" --model flux-2-pro --width 1024 --height 1024 -o out/

3. Edit with a reference image:

• flux edit "make it sunset lighting" --model flux-2-pro --input ./in.jpg -o out/

Commands

flux gen [prompt]

• text-to-image
• prompt can be positional, or - / stdin

flux edit [prompt] --input <path|url|base64> [--input ...]

• image editing using a prompt + 1..N input images (base + refs)

flux fill [prompt] --image <path|url|base64> [--mask <path|url|base64>]

• inpaint (explicit mask image, or alpha channel)

flux expand [prompt] --image <path|url|base64> [--top/--bottom/--left/--right <px>]

• outpaint (expand canvas by pixels on any side)

flux result <id> [--out <path|->]

• fetch status/result by id
• if status=Ready and --out is set, downloads the result

flux wait <id> [--polling-url <url>] [--out <path|->]

• wait until Ready/error; optionally download the result

flux credits

• show remaining credits

flux models

• list model keys supported by the CLI

flux config path|get|set|unset

• local config (including saving API key via stdin)

Global flags

• --json: single JSON object to stdout (for scripts)
• --plain: stable line output (paths/ids)
• -q, --quiet: less logging
• -v, --verbose: diagnostics to stderr (no secrets)
• --endpoint <host>: API host (default api.bfl.ai)
• --region <us|eu|global>: endpoint shortcut
• --timeout <ms>: timeout
• --retries <n>: retries for 429/5xx
• --out-dir <dir>: default output directory

Common gen/edit flags

• --model <key>: model key (see flux models)
• --seed <n>
• --safety <n>: safety_tolerance (range depends on model)
• --format <jpeg|png>: output_format
• -o, --out <path|->: file/dir or - for stdout
• --no-wait: submit only; print id (+ pollingUrl in --json)
• --poll-interval <ms>

Advanced (escape hatch):

• --body <json|@file>: raw request body (full control)

Models (keys)

Official model lineup evolves; use flux models for the current list.

Built-in keys, when to use them, and pricing tier (rule of thumb; pricing can change):

Footnote:

• MP-based: cost scales with output size in megapixels (width * height / 1,000,000). Larger images cost more.

Safety / reliability notes

• API key: avoid passing secrets via flags; use env/config/stdin.
• Signed URL: result.sample is typically short-lived; download immediately.

Editing best practices (Kontext)

Applies to flux edit with Kontext models (flux-kontext-pro, flux-kontext-max).

Prompt structure

• Max 512 tokens. Be explicit but concise.
• Be specific: exact color names, detailed descriptions, clear verbs.
• Preserve intentionally: state what must stay unchanged.
  • Bad: "Change to daytime"
  • Good: "Change to daytime while maintaining the same style of the painting"
• Name subjects directly: use descriptive identifiers, not pronouns.
  • Bad: "Transform her into a Viking"
  • Good: "Transform the woman into a viking warrior while preserving her exact facial features, eye color, and facial expression"
• Choose verbs carefully: “transform” signals complete replacement; “change the clothes to…” keeps identity.
• Control composition: when changing backgrounds, add "keeping the person in the exact same position, scale, and pose. Maintain identical camera angle, framing, and perspective."

Text editing in images

• Use quotation marks: Replace '[original text]' with '[new text]'
• Case formatting matters.
• Works on signs, posters, labels without full image recreation.

Annotation boxes

Bright colored boxes drawn on the input image act as spatial references.

• The model recognizes them automatically and removes them from output.
• Useful for targeted text repositioning, resizing, or pointing at a specific region.
• Example prompt: "Add hats in the boxes"

Iterative editing

• Kontext excels at character consistency across multiple sequential edits.
• Break complex transformations into steps for better control.
• Start simple; test basic edits before layering complexity.

Style transfer

• Name specific styles or reference known artists/art movements — not generic terms.
• Detail visual characteristics when style names are insufficient.
• For dramatic style shifts, use transformative sequences (multiple passes).
• Precise descriptions preserve structure: "Convert to pencil sketch with natural graphite lines, cross-hatching, and visible paper texture"

Common pitfalls

Common errors (exit codes)

• 2: invalid args/validation
• 3: missing key or 403
• 4: 402 (insufficient credits)
• 5: 429 (rate limit)
• 6: moderation
• 7: other API/task errors