Performance Guide

This guide covers performance optimization strategies for FastHTML apps built with Faststrap.

Static Assets

CDN Mode (Default)

from faststrap import add_bootstrap

add_bootstrap(app)
# Uses jsDelivr CDN for Bootstrap, Bootstrap Icons, and HTMX

CDN mode benefits: - No build step required - Assets cached across sites - Smaller app bundle

Local Mode

from faststrap import add_bootstrap

add_bootstrap(app, mode="local")

Local mode benefits: - Works offline - No external dependencies - Full control over asset versions

Hybrid Mode

from faststrap import add_bootstrap

add_bootstrap(
    app,
    mode="cdn",
    include_js=True,  # Include HTMX locally
)

Component Rendering

Use `include_js` Wisely

from faststrap import add_bootstrap

# Only include JS when needed
add_bootstrap(app, include_js=False)  # No JS
add_bootstrap(app, include_js=True)   # Full JS bundle

Lazy Load Components

from faststrap import LazyLoad

LazyLoad(
    "/api/heavy-component",
    target="#heavy-area",
    placeholder=Spinner(size="sm"),
)

Caching

Static File Caching

from faststrap import get_assets

assets = get_assets(app)
# Assets are cached with cache-control headers

Response Caching

from fasthtml.common import CacheControl

@app.get("/api/data")
def get_data():
    return JsonResponse(data, headers={"Cache-Control": "max-age=300"})

Database Queries

N+1 Prevention

# Bad: N+1 queries
items = db.query(Item).all()
for item in items:
    print(item.user.name)  # Extra query per item

# Good: Eager loading
items = db.query(Item).options(selectinload(Item.user)).all()

Service Worker (PWA)

from faststrap import PwaMeta

PwaMeta(
    name="My App",
    short_name="App",
    theme_color="#5B6CFF",
    background_color="#FFFFFF",
    start_url="/",
    display="standalone",
)

Service workers cache static assets for offline use and faster loads.

Monitoring

Response Times

import time

@app.before
def log_request_time(req, resp):
    start = time.time()
    yield
    elapsed = time.time() - start
    if elapsed > 0.5:
        print(f"Slow request: {req.url.path} took {elapsed:.2f}s")

Memory Usage

import tracemalloc

tracemalloc.start()

# ... app code ...

snapshot = tracemalloc.take_snapshot()
top_stats = snapshot.statistics("lineno")
for stat in top_stats[:10]:
    print(stat)