/huggingface-spaces

Gradio for Spaces

Patterns and quirks specific to running Gradio inside a Space. Assumes you're already comfortable with stock Gradio components and gr.Blocks / gr.Interface.

For deeper Gradio API guidance — components, layouts, event listeners, chatbots, the Gradio 5→6 migration — use the dedicated huggingface-gradio skill. Install it with hf skills add huggingface-gradio (add --claude --global to also install for Claude Code, user-level).

For ZeroGPU-specific decorator + worker semantics, see zerogpu.md.

Themes and layout

• Default theme preference: gr.themes.Citrus(). Alternatives: gr.themes.Soft() or no theme. Pick once and don't over-style.
• For apps that don't need full-width, constrain with CSS so they're readable on 4K displays:

  CSS = """
  #col-container { max-width: 1100px; margin: 0 auto; }
  .dark .gradio-container { color: var(--body-text-color); }
  """
  with gr.Blocks(theme=gr.themes.Citrus(), css=CSS) as demo: ...

  Always include the .dark .gradio-container override with gr.themes.Citrus() — without it Citrus's dark mode renders dark text on a dark background (text inherits unset colors). The same fix is harmless (and worth keeping) under other themes.
• Width-cap with !important if Gradio 6's own breakpoints fight you — target main, .gradio-container, and the inner fillable wrapper, otherwise the width caps but goes flush-left.

Minimal layout most demos converge to

with gr.Row():
    prompt = gr.Textbox(show_label=False, placeholder="…", container=False, scale=4)
    run = gr.Button("Run", variant="primary", scale=1)
output = gr.Image(...)
with gr.Accordion("Advanced settings", open=False):
    ...

container=False on the inline Textbox removes the default outer border for a tighter look.

gr.Markdown for the intro

Be succinct. Title, one-line description, a links section. Don't over-explain how it works — that's what the model card is for.

gr.Examples

Add gr.Examples whenever it makes sense (the app takes user input and representative inputs exist). It's the first thing a visitor clicks and it doubles as an instant smoke test. Prefer examples that mirror the official examples from the original repo / model card — the prompts, images, and settings the authors showcase — over inventing your own.

Keep each example row to the few variables a user actually changes (the prompt, the input image). Give the handler default values for everything else (steps, guidance, seed, …) so an example row is ["a cat on a windowsill"], not a wall of knobs. Design the signature so the interesting inputs come first and the rest default:

@spaces.GPU(duration=60)
def generate(prompt, seed=42, steps=28, guidance=5.0):   # only `prompt` varies in examples
    ...

gr.Examples(
    examples=[
        ["a cat sitting on a windowsill"],
        ["mountains at sunset, photorealistic"],
    ],
    inputs=[prompt],          # just the varied inputs; the rest use the handler defaults
    outputs=output,
    fn=generate,
    cache_examples=True,
    cache_mode="lazy",
)

Why these flags:

• cache_examples=True makes example clicks instant (no re-inference per visitor).
• cache_mode="lazy" — caches on first user click for each example. Required on ZeroGPU (Gradio's default on ZeroGPU is already lazy via GRADIO_CACHE_MODE=lazy). Eager would pre-run every example at app startup, but ZeroGPU has no GPU attached at startup — it'd fail and burn the creator's daily quota.
• cache_examples=True silently disables run_on_click / run_examples_on_click. If your app relies on click-only behavior, set cache_examples=False.

The cache key is the example row's file path, not a content hash. Regenerating an asset in place serves the stale cached output forever. If you replace example files, bump a cache_version marker or wipe .gradio/cached_examples/<id>/.

Hot-reload (rung 1) does not rebuild the cache. A cache_version bump needs a real commit + restart.

Streaming and generators

gr.Interface(fn=...) and .click(fn=...) both accept generator functions. Each yield pushes a new value:

@spaces.GPU(duration=120)
def generate(prompt):
    yield gr.update(value=None, label="Starting…")
    for k in range(num_steps):
        yield gr.update(value=preview(k), label=f"Step {k+1}/{num_steps}")
    yield gr.update(value=final, label="Done")

Use gr.update(label=...) for status narration — feels like a status line without a separate component.

Caveat: gr.Progress(track_tqdm=True) and yield partial outputs fight each other — pick one streaming mechanism.

Useful UX bits

• progress=gr.Progress(track_tqdm=True) in the GPU function gives a free tqdm-driven progress bar.
• Pair a "Randomize seed" checkbox with the seed input, and write the actually-used seed back so users can re-run deterministically:

  randomize = gr.Checkbox(label="Randomize seed", value=True)
  seed = gr.Number(label="Seed", value=0, precision=0)
  
  @spaces.GPU
  def gen(..., seed, randomize_seed):
      if randomize_seed:
          seed = random.randint(0, 2**31 - 1)
      seed = int(seed)
      yield ..., gr.update(value=seed)   # write back into the Seed input
      ...
  
  run.click(gen, inputs=[..., seed, randomize], outputs=[..., seed])

Custom HTML components

Stock Gradio components cover 95% of cases. When they don't, gr.HTML(...) lets you build contextual custom UI without leaving the Gradio Space (no need to switch to Docker).

Guide: https://www.gradio.app/guides/custom-HTML-components Example with a 3D camera-angle picker that makes sense in context: https://huggingface.co/spaces/multimodalart/qwen-image-multiple-angles-3d-camera

Don't reach for this if a stock component covers the need.

Custom frontends — gr.Server

For fully custom frontends with their own HTML/JS, while keeping Gradio's queue + GPU scheduling:

from gradio import Server
from fastapi.responses import HTMLResponse

app = Server(title="my-app")

@spaces.GPU(duration=60)
def _run_gpu(prompt): return inference(prompt)

@app.api(name="generate", concurrency_limit=1, time_limit=180)
def generate(prompt: str) -> str:
    return _run_gpu(prompt)        # @app.api wraps, doesn't stack with @spaces.GPU

@app.get("/", response_class=HTMLResponse)
async def homepage():
    return open("index.html").read()

demo = app                          # HF runtime expects `demo`
if __name__ == "__main__":
    demo.launch(ssr_mode=False)

Required for the custom / route to actually serve:

hf spaces variables add <ns>/<name> --env GRADIO_SSR_MODE=false

launch(ssr_mode=False) is ignored on HF — must be the env var.

Valid @app.api kwargs: name, description, concurrency_limit, concurrency_id, queue, batch, max_batch_size, api_visibility, time_limit, stream_every.

Don't stack @spaces.GPU and @app.api on the same function — silently breaks request flow. Keep them on separate functions.

Two-ceiling coordination: both @spaces.GPU(duration=N) and @app.api(time_limit=M) apply; the lower wins. Set time_limit to your max duration across modes — a too-low time_limit kills the request even if GPU duration would have allowed it.

Hot-reload (rung 1 in debugging.md) does not work with gr.Server — always hf upload or commit.

Reference Space: https://huggingface.co/spaces/huggingface-projects/rf-detr-realtime-webcam

Slow-startup Gradio (big-model Spaces)

For Spaces that take 10–20 min to load weights:

• Set startup_duration_timeout: 1h in README frontmatter (default 30 min).
• Disable SSR: hf spaces variables add <id> --env GRADIO_SSR_MODE=false. Otherwise the SSR health check times out before the app finishes loading.

Expose the Space as an MCP server

Launch with demo.launch(mcp_server=True) (Gradio 5+) so every API endpoint is also exposed as an MCP tool — free, and makes the Space usable by agents. For it to be useful:

• Every API-triggered function needs a docstring and type hints. Each Gradio event handler is auto-exposed over the API; Gradio turns the signature into the MCP tool's input schema and the docstring into its description. A function without them still works but surfaces as an opaque, unusable tool.
• Give the important endpoints stable names (api_name="generate" on the .click(...), or @app.api(name=...)), so tool names don't churn.
• MCP mode can pull in extra deps (gradio[mcp]); if launch complains, see the pin note in known-errors.md.

@spaces.GPU(duration=60)
def generate(prompt: str, seed: int = 42) -> str:
    """Generate an image from a text prompt.

    Args:
        prompt: what to generate.
        seed: RNG seed for reproducibility.
    """
    ...

btn.click(generate, inputs=[prompt, seed], outputs=out, api_name="generate")
demo.launch(mcp_server=True)

Don't

• gr.Button(text="X") — text= was removed; use gr.Button("X").
• gr.Button(type="button") — drop the kwarg.
• .click(..., _js=share_js) — renamed to js=.
• .style(height=...) — removed in gradio 4+.
• gr.ImageMask(brush_color=...) — kwarg removed.
• demo.launch(mcp_server=True) on gradio 4.x — only valid on 5+.