HTTP Cookie Inspector — Parse & Debug Cookie Headers Instantly

HTTP Cookie Inspector is a free, browser-based developer tool that decodes Cookie and Set-Cookie HTTP header strings into structured, human-readable output. Paste a header value, see every attribute parsed and explained, and get instant security warnings — no setup, no signup, no data leaving your browser.

The Problem

Cookie debugging is surprisingly tedious. When a session breaks or an auth cookie doesn't persist, you're staring at a raw header string like:

session=abc123; Domain=example.com; Path=/; Expires=Fri, 31 Dec 2027 23:59:59 GMT; Max-Age=63072000; HttpOnly; Secure; SameSite=Strict

Parsing that mentally — especially for expiry calculations or cross-checking security attributes — wastes time. Most developers paste headers into a text editor and count semicolons. Some Google each attribute individually. Neither approach flags missing security flags or tells you the cookie expires in 47 days at 23:59 UTC.

HTTP Cookie Inspector cuts this down to under 2 seconds.

How It Works

1. Choose Header Type

Switch between two modes using the tab toggle:

• Cookie (Request) — the header sent by the browser, containing one or more name=value pairs
• Set-Cookie (Response) — the header sent by the server, with a single cookie and all its attributes

2. Paste the Header Value

Paste the raw value (no need to include the header name itself). Load one of the built-in examples to see the tool in action immediately.

3. Inspect Parsed Output

Cookie mode displays a clean table of every name=value pair with one-click copy for each value.

Set-Cookie mode shows:

• Cookie name and value
• Domain, Path, and Expiry (with human-readable "expires in 47d 2h" format)
• Security attribute badges: HttpOnly, Secure, SameSite
• Security warnings for any missing or misconfigured flags

Key Features

• Two-mode parsing — Cookie request headers and Set-Cookie response headers
• Security validation — flags missing HttpOnly, Secure, SameSite; validates __Secure- and __Host- cookie prefixes; warns on SameSite=None without Secure
• Human-readable expiry — converts Expires and Max-Age to "in 2d 14h" relative time
• One-click copy — copy any name, value, or raw input instantly
• Built-in examples — load realistic cookie strings to explore features immediately
• 100% client-side — your cookie data never leaves your browser
• No signup required — start using immediately

Technical Implementation

Core Technologies

• Next.js with App Router
• TypeScript in strict mode
• TailwindCSS v4 for styling
• shadcn/ui for accessible components
• Framer Motion for animations

Architecture

• Pure TypeScript cookie parser — no DOM cookie API, no external libraries
• Handles all standard Set-Cookie attributes: Domain, Path, Expires, Max-Age, HttpOnly, Secure, SameSite
• Max-Age takes precedence over Expires when both are present (per RFC 6265)
• Cookie prefix validation: __Secure- and __Host- requirements checked automatically
• Relative expiry formatter handles seconds, minutes, hours, and days

Security

• All parsing is client-side — cookie values are never transmitted
• No document.cookie access — tool reads only what the user pastes in
• Safe for use with session tokens, JWTs, and auth cookies

Use Cases

Debugging Broken Sessions

Your users are getting logged out unexpectedly. Paste the Set-Cookie header from your login response and immediately see if Max-Age is shorter than expected, or if Secure is missing and the cookie is being dropped on HTTPS.

Auditing Cookie Security

Copy the Set-Cookie header from any authentication endpoint and run it through the inspector. The security validator instantly tells you whether HttpOnly, Secure, and SameSite are correctly set — no manual attribute counting.

Understanding Cookie Prefixes

The __Secure- and __Host- prefixes enforce additional security requirements. If you're using them incorrectly, browsers silently reject the cookie. The inspector validates these prefixes and tells you exactly what's wrong.

Cross-Browser Testing

Cookie behaviour varies across browsers. Understanding the exact attributes set by your backend helps predict how cookies will behave in Safari's ITP, Firefox's enhanced tracking protection, and Chrome's SameSite enforcement.

Learning and Documentation

Writing documentation about cookie security for your team? Use the inspector to generate clear visual examples of correctly vs. incorrectly configured cookies.

API Development

Integrating a third-party API that sets cookies? Paste the Set-Cookie response header to understand the session lifecycle, domain scope, and security posture before writing integration code.

Security Validation Rules

The inspector checks for common cookie security issues:

| Issue | Severity | Explanation | |---|---|---| | Missing Secure flag | Warning | Cookie sent over HTTP — vulnerable to interception | | Missing HttpOnly flag | Warning | JavaScript can read the cookie via document.cookie | | Missing SameSite attribute | Warning | Browser defaults may vary; set explicitly | | SameSite=None without Secure | Warning | Browsers reject SameSite=None cookies without Secure | | __Secure- prefix without Secure | Warning | Prefix requirement not met; browsers will reject | | __Host- prefix issues | Warning | Requires Secure, no Domain, and Path=/ |

Why HTTP Cookie Inspector?

vs. Browser DevTools

• Paste-and-inspect — works without a live request in flight
• Security validation — DevTools shows attributes but doesn't warn about missing security flags
• Human-readable expiry — DevTools shows raw timestamps; inspector shows "expires in 47d"
• Shareable — paste a cookie string into a Slack message, then inspect it here

vs. Manual Parsing

• Instant — parse any cookie string in under 2 seconds
• No mistakes — attribute parsing is exact, no manual semicolon splitting
• Validated — security rules checked automatically
• Visual — colour-coded badges make missing flags immediately obvious

Results

HTTP Cookie Inspector removes friction from a task that every backend and frontend developer runs into repeatedly:

• Under 2 seconds to fully parse and validate any Set-Cookie header
• Zero missed security flags — the validator catches what manual review misses
• 100% private — session tokens and auth cookies stay in your browser
• No friction — no signup, no install, no configuration

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Try it now: http-cookie-inspector.tools.jagodana.com