Essential Checklist Before Launching a Web Application: UI, Security, Performance, SEO

UI and User Experience

Ensure cross‑browser compatibility (Gecko, WebKit, Chrome, IE, Opera) and test on different operating systems.

Consider alternative access methods such as mobile devices, screen readers, and search engines (WAI, Section508, MobiForge).

Use staging environments and automated deployment with version control (Git, CVS, Subversion) and build tools (Ant, NAnt).

Avoid unfriendly error messages and exposing raw email addresses.

Add rel="nofollow" to user‑generated links to reduce spam.

Implement progressive enhancement and redirect after successful POST to prevent duplicate submissions.

Address accessibility (WAI‑ARIA, WCAG 2) and make interactions intuitive.

Security

Read the OWASP Development Guide for comprehensive web security.

Understand injection attacks, especially SQL injection, and how to prevent them.

Never trust user input, cookies, or hidden form fields.

Hash passwords with a slow algorithm (bcrypt, scrypt, PBKDF2) and unique salts; avoid MD5 or plain SHA.

Do not design custom authentication schemes without thorough review.

Follow credit‑card handling rules and always use SSL/HTTPS for sensitive pages.

Protect against session hijacking, XSS, CSRF, click‑jacking, and keep systems patched.

Secure database connection information and stay informed about new vulnerabilities.

Read Google’s Browser Security Manual and the Web Application Hacker’s Handbook.

Apply the principle of least privilege and run services as non‑root where possible.

Performance

Implement caching (HTTP caching, HTML5 offline cache) when appropriate.

Optimize images and avoid large repeated background files.

Compress content with gzip/deflate (deflate is often better).

Combine CSS and JavaScript files to reduce HTTP requests and use gzip for the combined files.

Use tools like Yahoo! Exceptional Performance, YSlow, and Google PageSpeed for profiling and optimization.

Employ CSS sprites for small related images.

Serve static assets (images, CSS, JS) from a separate, cookie‑free domain or CDN, with a fallback for CDN failures.

Minimize the number of HTTP requests required to render a page.

Compress JavaScript with Google Closure Compiler or similar tools.

Provide a /favicon.ico file to avoid unnecessary 404 errors.

SEO (Search Engine Optimization)

Use search‑engine‑friendly URLs (e.g., /pages/45-article-title instead of query strings).

Avoid generic link text like “click here”.

Maintain an XML sitemap at /sitemap.xml.

When duplicate URLs exist, specify a canonical link.

Utilize Google and Bing Webmaster Tools and install analytics early.

Understand robots.txt and crawler behavior.

Implement 301 redirects to consolidate domain authority.

Know that not all crawlers are beneficial.

Include non‑text content (e.g., video) in the sitemap when appropriate.

Technical

Master HTTP fundamentals (GET, POST, sessions, cookies) and the stateless nature of the protocol.

Write valid XHTML/HTML and CSS per W3C specifications.

Understand how browsers process JavaScript, resource loading, and performance impact.

Be aware of JavaScript sandboxing, iframe usage, and the possibility of disabled JavaScript.

Distinguish between 301 and 302 redirects.

Learn the deployment platform’s specifics.

Consider reset stylesheets or normalize.css.

Leverage JavaScript frameworks (jQuery, MooTools, Prototype, Dojo, YUI) to handle cross‑browser differences.

Load frameworks from CDNs when possible to benefit from cached copies.

Avoid reinventing the wheel; reuse existing open‑source components.

Keep libraries lightweight and avoid over‑loading the client.

Bug Fixes

Allocate time for both coding (≈20%) and maintenance (≈80%); prioritize code quality.

Implement robust error‑reporting mechanisms.

Provide a feedback system for users.

Document the system for future maintainers.

Perform regular backups and have a reliable restore process.

Use version control (Subversion, Mercurial, Git).

Conduct acceptance testing; automate with tools like Selenium and CI servers such as Jenkins.

Maintain comprehensive logging (log4j, log4net, log4r) to diagnose issues.

Other

Monitor both server‑side and client‑side performance proactively.

Engage users with communication tools (UserVoice, Intercom, etc.).

Adopt Git branching models like Vincent Driessen’s workflow.

These points form a thorough checklist that developers should review to ensure a stable, secure, performant, and searchable web application before it goes live.