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niuniu
niuniu

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Quick Tip: `curl -w` Measures DNS, TLS, and TTFB Without Any Tools

#python #coding #tips

Quick Tip

You just deployed to a free tier. Is it slow, or is it your internet? One curl command tells you exactly where the time goes:

curl -w "\nDNS: %{time_namelookup}s\nTCP: %{time_connect}s\nTLS: %{time_appconnect}s\nTTFB: %{time_starttransfer}s\nTotal: %{time_total}s\n" \
  -o /dev/null -s https://your-app.fly.io/health
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Output:

DNS: 0.001s
TCP: 0.012s
TLS: 0.089s
TTFB: 0.412s
Total: 0.445s
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What each phase tells you

Phase If it's slow Fix
DNS Your DNS provider or no CDN Move to Cloudflare (free)
TCP Server is far away or overloaded Pick a closer region
TLS Certificate chain or old TLS Let's Encrypt + TLS 1.3
TTFB Your app is slow (cold start, DB query) Optimize code or upgrade tier

The free-tier cold start detector

Run this twice, 5 minutes apart:

# First hit (cold)
curl -w "TTFB: %{time_starttransfer}s\n" -o /dev/null -s https://your-app.onrender.com/

# Second hit (warm)
curl -w "TTFB: %{time_starttransfer}s\n" -o /dev/null -s https://your-app.onrender.com/
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If TTFB drops from 14s to 0.2s, your free tier spins down. That's not a bug — it's the business model.

The one-liner I keep in my dotfiles 

alias curltime='curl -w "\nDNS: %{time_namelookup}s | TCP: %{time_connect}s | TLS: %{time_appconnect}s | TTFB: %{time_starttransfer}s | Total: %{time_total}s\n" -o /dev/null -s'
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No install. No dependencies. Works on every server, every CI runner, every Docker container you'll ever debug.

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What's your go-to one-liner for diagnosing slow endpoints? I keep finding new uses for curl -w and it keeps replacing tools I used to install.

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