Observed Signal · Jul 24, 2026 · Technical Release · Source: DEV Community · Impact: 2/5 · Sentiment: Positive
Real Speedtest in Vanilla JS with Cloudflare API
A developer built a fully client-side speedtest in a single HTML file (~50 KB) using the public Cloudflare Speedtest API (speed.cloudflare.com). The tool measures HTTP-based ping (via small fetches and performance.now()), download speed (using the Streams API and response.body.getReader() to count chunks in real time), and upload speed (using XMLHttpRequest upload.onprogress with a fetch fallback). The UI is an SVG gauge animated with requestAnimationFrame. Users can enter their contracted tariff and the tool compares measured throughput to that tariff. The author highlights practicality (no frameworks or npm), anti-compression payloads for uploads, and Cloudflare’s permissive CORS and unauthenticated endpoints.
Demonstrates a lightweight, client-side method to measure real user network performance using public CDN endpoints (Cloudflare), which is useful to web developers and publishers but is not industry-shifting.
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Key Takeaways & Evidence Grounding
- The speedtest is implemented in a single HTML file delivered under ~50 KB with ~250 lines of JavaScript.
- It uses Cloudflare's public Speedtest API endpoints at speed.cloudflare.com: __down?bytes=N for downloads and __up for uploads.
- Ping is measured via HTTP RTT by fetching a 1 KB resource multiple times and using performance.now() to compute round-trip times.
- Download measurement streams received data with the Streams API (response.body.getReader()) to compute live Mbps and progress.
- Upload measurement uses XMLHttpRequest with upload.onprogress and a pseudo-random 8 MB payload to avoid compression; a fetch-based fallback is provided when XHR progress is unavailable.
Connected Companies & Entities
1 Entity mapped“For all three measurements the author uses the public Cloudflare Speedtest API, which runs at speed.cloudflare.com and allows CORS so measur...”
Ontology Mapping & Concepts
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