If you run a website, your HTTP response headers are the first thing a browser sees before it renders a single pixel. They tell the browser how to behave, what to cache, and crucially — how to protect your users. Yet most developers never actually read their headers, let alone audit them.

I used to be one of them. I’d set up a server, enable HTTPS, maybe add an HSTS line if I remembered, and move on. It wasn’t until I joined a security-conscious team that I realized how many critical protections were missing from my projects. And when I looked for a simple, free tool to analyze my headers, I found that the existing options were either too technical, too slow, or too opaque.

So I built one myself. DevToolbox HTTP Header Analyzer grades your security headers from A+ to F, explains every header in plain English, and tells you exactly what to fix — all without sending your data to any server.

What It Does (That Other Tools Don’t)

1. Instant Security Score (A+ to F) Paste any HTTP response headers, and you get a numerical score out of 100 along with a letter grade. The grading is transparent:

A+ (95–100): all critical security headers present and correctly configured.

A (85–94): solid, with minor gaps.

B (70–84): decent, but missing some important protections.

C, D, F: significant or critical security headers missing.

Under the hood, points are deducted for each missing or misconfigured header, weighted by risk (HSTS and CSP are worth 25 points each; X-Powered-By exposure is 5 points).

1. Plain-English Explanations for Every Header Instead of staring at Strict-Transport-Security: max-age=31536000; includeSubDomains and wondering if it’s good enough, the tool tells you:

“HSTS instructs the browser to always connect to this domain using HTTPS for the next 365 days. The includeSubDomains directive extends this to all subdomains. ✅”

It also flags dangerous values like unsafe-inline in your CSP and explains why they weaken your security.

1. Actionable Fixes For every missing or failing security header, you get a copy-paste ready fix. For example:

Missing HSTS → add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;

X-Powered-By exposed → app.disable('x-powered-by') (Express) or expose_php = Off (PHP)

No need to google the syntax.

1. Before / After Comparison Mode
   Making changes to your Nginx config? The compare mode lets you paste your old headers and new headers side by side. The tool shows the security score for each, highlights added/removed/changed headers with color-coded diffs, and proves that your fix actually improved things.

2. 100% Client-Side — Your Headers Stay Private
   The analysis runs entirely in your browser. You can paste sensitive production headers without worrying about them being sent to a third-party API. This is especially important if your headers contain internal domain names, IP addresses, or server version strings.
   How It Compares to Popular Alternatives
   Feature DevToolbox SecurityHeaders.com Mozilla Observatory
   Security grading (A+ to F) ✅ ✅ ✅ (0–100)
   Plain-English explanations ✅ (every header) ❌ ⚠️ (basic)
   Fix suggestions ✅ ❌ ❌
   Before / after comparison ✅ ❌ ❌
   Analysis of non-security headers (caching, CORS) ✅ ❌ ❌
   Client-side, no URL scanning ✅ ✅ (scans by URL) ✅ (scans by URL)
   Free ✅ ✅ ✅
   Unlike SecurityHeaders.com, which only tells you what is missing, DevToolbox also explains why it matters and how to fix it. And unlike Mozilla Observatory, which requires fetching a live URL, DevToolbox works offline — you can paste headers from a local development server that isn’t even publicly accessible.

A Real-World Example
Let’s say I run a small app with this Nginx config:

server {
    listen 443 ssl;
    server_name example.com;
    add_header X-Frame-Options DENY;
}

I paste the response headers into the analyzer. Immediately, I see:

Grade: D (45/100)

🔴 HSTS missing (critical) — my users are vulnerable to SSL stripping attacks.

🟠 CSP missing — no XSS protection.

🟠 Referrer-Policy not set — URLs may leak query parameters.

🟡 X-Content-Type-Options missing — MIME sniffing possible.

✅ X-Frame-Options present — clickjacking covered.

The tool gives me the exact add_header lines to fix everything. I add them, reload Nginx, paste the new headers, and the grade jumps to A+ (97/100).

The Bigger Picture: A Suite of Privacy-First Developer Tools
The HTTP Header Analyzer is part of DevToolbox, a free collection of client-side tools I’m building. The philosophy is simple: if a tool can run in your browser, it should. No uploads, no accounts, no tracking.

You might also want to check out:

🔐 JWT Decoder & Security Analyzer — finds alg:none and algorithm confusion attacks

⏱ Universal Timestamp Converter — Unix, ISO, FILETIME, UUID, ObjectID

🎨 CSS Effects Generator — glassmorphism, neumorphism, keyframes

🧹 SQL Formatter & Explainer — formatting, anti-pattern detection, dialect conversion

All free, no sign-up required.

Try It Out
Grab your headers with curl -I https://yoursite.com (or from DevTools → Network → Response Headers) and paste them into:

👉devstoolsbox

You might be surprised by your grade. Let me know in the comments what score you got and what you fixed — I’d love to hear real-world stories!