Blog
Guides and tutorials for developers — file upload testing, image optimization, data handling, and more.
5 Browser File API Gotchas: Memory, Slicing & Metadata
Five reproducible Browser File API pitfalls involving data URLs, Blob slicing, lastModified metadata, file input events, and whole-file buffering.
Generate Sample Files in the Browser (No Upload Needed)
How to generate sample files locally with Blob, TextEncoder, Uint8Array, object URLs, and a custom file size up to 1GB. No upload or backend required.
MIME Type Detection in Production — A Practical Validation Pipeline
Build a defensible MIME detection pipeline with client hints, magic bytes, text sniffing, parser validation, and explicit confidence levels.
Safe Dummy File Generator with No Upload
Create private dummy files locally in your browser with a custom file size up to 1GB. No upload, no signup, and no server storage.
Test Upload Forms with Generated Files
A practical workflow for testing upload forms with generated TXT, CSV, JSON, XML, BIN, and SVG files. Includes custom file size checks up to 1GB.
Archive Formats Cheat Sheet — ZIP vs RAR vs 7Z vs TAR.GZ
Quick-reference comparison of archive formats: ZIP, RAR, 7Z, TAR.GZ, TAR.BZ2, TAR.XZ. Compression ratio, speed, encryption, OS support, and licensing.
Audio Formats Cheat Sheet — MP3 vs AAC vs FLAC vs WAV vs OGG
Quick-reference comparison of audio formats: MP3, AAC, OGG, FLAC, WAV, Opus. Bitrate, quality, file size, compatibility, and streaming support at a glance.
File Size Limits Cheat Sheet — Email, Cloud & Social Media
Reference guide to common file size limits across Gmail, Outlook, S3, GCS, Instagram, TikTok, YouTube, Discord, WhatsApp, and Telegram.
File Type Validation Beyond Extensions — Magic Bytes, MIME Sniffing, and Polyglots
Why file extension checking is not enough. Learn magic bytes validation, MIME sniffing attacks, polyglot files, and how to properly validate file types with real sample files.
File Upload Security Checklist — 10 Steps Every Developer Must Follow
Complete file upload security checklist: MIME validation, magic bytes, file size limits, malware scanning, filename sanitization, storage isolation. Node.js and Python code.
Fix Corrupt File Upload Errors — Why Uploaded Files Get Corrupted
Debug and fix corrupted file uploads. Covers encoding issues, incomplete transfers, wrong Content-Type, binary vs text mode, and multipart boundary errors. With test files to reproduce.
Fix CSV Encoding Issues — UTF-8 BOM, Delimiters, and Character Errors
Fix CSV parsing errors: UTF-8 BOM causing extra characters, wrong delimiter detection, newlines in fields, mojibake characters. With sample CSVs to reproduce.
Fix 413 Payload Too Large — File Upload Size Limit Errors
Fix HTTP 413 Request Entity Too Large errors. Configure max file size in Nginx, Apache, Express, Next.js, PHP, and cloud platforms. Test with exact-size sample files.
Fix Broken Images — Why Images Won't Display in Browser
Debug broken images: wrong MIME type, CORS errors, corrupted data, missing files, wrong format. Complete checklist with test images to reproduce each issue.
Fix Unsupported File Type Errors — MIME Type & Extension Validation
Fix 'Unsupported file type' and 'Invalid file format' errors. Learn MIME type detection, magic bytes validation, extension whitelisting, and how to handle MIME type spoofing.
Fix Video Not Playing in Browser — Codec, MIME, and CORS Errors
Debug HTML5 video playback: unsupported codec, wrong MIME type, CORS blocked, missing Range headers, and HLS issues. With test videos to reproduce each problem.
How to Fix ZIP Extraction Errors: 7 Common Causes
Diagnose ZIP extraction errors caused by corruption, wrong file types, passwords, compression methods, filenames, disk limits, or unsafe paths.
Image Formats Cheat Sheet — Complete Comparison Table
Quick-reference comparison of every image format: JPEG, PNG, WebP, AVIF, HEIC, GIF, SVG, TIFF, BMP. Lossy/lossless, transparency, animation, browser support, and best use cases.
Image Metadata Privacy Risks — EXIF Data Leaks and How to Strip Them
EXIF metadata in photos exposes GPS location, camera model, timestamps, and software. Learn how to strip metadata with sharp, ImageMagick, Pillow, and ExifTool.
Load Testing File Uploads with k6 — Performance Testing Guide
k6 scripts for load testing file upload endpoints. Download sample files from TrueFileSize, simulate concurrent uploads, and measure throughput, latency, and error rates.
MIME Types Cheat Sheet — Common Content-Types for Web Developers
Complete MIME type reference grouped by category with copy-paste snippets for Nginx, Apache .htaccess, and Express.js. Bookmark this for Content-Type configuration.
Preventing Zip Bomb Attacks — Detection and Safe Extraction
What is a zip bomb, how it works (42.zip, nested recursion, quine), detection techniques, safe extraction with size limits, and testing with sample ZIPs.
Using Sample Files in CI/CD Pipelines — GitHub Actions & GitLab CI
How to download, cache, and use sample test files in CI/CD pipelines. GitHub Actions and GitLab CI examples with caching, parallel tests, and artifact handling.
Secure File Download Implementation — Headers, Signed URLs, and Access Control
Implement secure file downloads: Content-Disposition headers, path traversal prevention, signed URLs (S3/R2), access control, rate limiting, and audit logging.
Seeding Test Databases with Sample Data — SQL, JSON, CSV
How to seed development and staging databases using sample SQL dumps, JSON files, and CSV imports from TrueFileSize. Covers PostgreSQL, MySQL, SQLite, MongoDB, and Prisma.
Testing File Upload with Cypress — Using Real Sample Files
Complete guide to testing file upload in Cypress E2E tests. Download sample PDF, image, and video files from TrueFileSize, upload via cy.selectFile(), and assert results.
Testing File Upload with Playwright — Cross-Browser E2E Guide
Test file upload in Playwright across Chrome, Firefox, and Safari. Download sample files from TrueFileSize, use setInputFiles(), and test drag-drop, progress, and error handling.
Testing Image Processing Pipelines with Sample Files
Test sharp, ImageMagick, and Pillow image processing using sample PNG, JPG, WebP, AVIF files from TrueFileSize. Resize, convert, optimize, and validate output.
Testing S3 Upload with Sample Files — Presigned URLs & Multipart
Test AWS S3 file uploads using sample files from TrueFileSize. Covers presigned URLs, multipart upload for large files, and integration testing with LocalStack.
Video Codecs Cheat Sheet — H.264 vs H.265 vs VP9 vs AV1
Quick-reference comparison of video codecs: H.264, H.265/HEVC, VP9, AV1. Quality, file size, encoding speed, hardware support, licensing, and browser compatibility.
Audio Upload Validation and Server-Side Transcoding
Validate audio uploads, check real format, and transcode with ffmpeg on the server. Sample MP3, WAV, OGG, and AAC files for every edge case.
Benchmarking CDN Download Speeds
Measure real-world download speed across CDNs with curl and Node.js. Sample files from 1MB to 10GB for speed, latency, and geographic testing.
Chunked Video Upload with Resumable Transfers
Testing large video uploads with chunked, resumable transfers. tus protocol, multipart uploads, and progress tracking. Sample MP4 files up to 500MB.
Database Seeding from SQL Dumps
Populate test databases with realistic data. MySQL, PostgreSQL, and SQLite sample dumps. Fixtures for users, orders, and time-series data.
HLS vs MP4 for Video Streaming
Adaptive streaming with HLS vs progressive MP4 download. Which one to use, when, and how to test each approach. Sample videos for both formats.
Image Optimization for Web Performance
A reproducible image optimization workflow using modern formats, responsive srcset, lazy loading, and measured LCP improvements.
How to Handle Large File Uploads — Performance Guide
Complete guide to handling large file uploads (100MB+). Covers chunked upload, resumable transfers, progress tracking, and testing with sample files.
Mocking REST APIs with JSON Fixtures
Fast frontend iteration without a backend. MSW, json-server, and sample fixtures for users, products, and nested objects. Copy-paste examples.
Handling Password-Protected Archives
Testing ZIP, RAR, and 7Z archives with passwords. Libraries, AES encryption, and brute-force protection. Sample encrypted archives included.
PDF Parsing and Text Extraction — A Practical Guide
Extract text, metadata, and structure from PDF files with pdf.js and pdf-parse. Handle scanned PDFs with OCR. Use sample PDFs plus large test files for stress cases.
Resumable Uploads with the tus Protocol
Production-grade file uploads that survive network drops. tus-js-client, server implementations, and large test files to validate your setup.
Sample CSV Files for Pandas Testing
Free sample CSV files optimized for Python pandas testing. Learn to load, analyze, and benchmark with datasets from 100 to 1 million rows.
Sample JSON Data for API Testing and Mocking
Free sample JSON files for testing REST APIs. Users, products, nested objects, GeoJSON, and API response wrappers with code examples.
Server-Side ZIP Extraction — Security and Performance
Safely extracting ZIP uploads in Node.js and Python. Zip-slip prevention, memory limits, and streaming extraction. Sample ZIPs for every scenario.
SVG vs PNG for Icons — Which Format Should You Use?
When to use SVG, when to use PNG for favicons and UI icons. Accessibility, animation, file size, and caching — with side-by-side samples you can copy.
How to Test File Upload in React — With Sample Files
Learn how to test file upload functionality in React apps using sample PDF, image, and video files. Covers unit tests, integration tests, and E2E testing.
How to Test Video Upload — Sample Videos and Code Examples
Guide to testing video upload in web apps. Sample MP4 files from 1MB to 500MB, HTML5 video validation, and server-side processing.
Testing Word and Excel Uploads in Production
Validating DOCX and XLSX uploads — size limits, macro detection, corrupted files, and viewer compatibility. Sample office files for every edge case.
WAV vs MP3 vs OGG for Web Audio
Choosing the right audio format for your web app. Browser support, file size, quality, and streaming behavior. Sample files in all three formats.
WebP vs PNG vs JPG — Which Format Should You Use?
Comprehensive comparison of WebP, PNG, and JPG image formats. File size, quality, browser support, and when to use each format.