Blog
Guides and tutorials for developers — file upload testing, image optimization, data handling, and more.
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.
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.
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. Sample PDFs from 1KB to 100MB for every test case.
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.
Image Optimization for Web Performance
Modern formats, responsive srcset, lazy loading, and CDN tricks. Cut LCP by 40% with proper image optimization. Sample JPG, PNG, and WebP files included.
SVG vs PNG for Icons — Which Wins in 2025?
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.
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.
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.
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.
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.
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.
5 Browser File API Gotchas That Will Waste Your Weekend
FileReader memory leaks, Blob.slice() Safari bugs, broken lastModified on mobile, the onChange non-event, and iOS size limits. Hard-won lessons from production file upload code.
MIME Type Detection in Production — Lessons from Processing 10 Million Files
The browser's Content-Type header lies. Here's what actually works for MIME detection at scale — library benchmarks, the edge cases nobody warns you about, and a decision tree for production.
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.
Handling Password-Protected Archives
Testing ZIP, RAR, and 7Z archives with passwords. Libraries, AES encryption, and brute-force protection. Sample encrypted archives included.
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.
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.
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.
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.
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 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 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 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 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.
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.
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.
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.
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.
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.
Image Formats Cheat Sheet — Complete Comparison Table (2025)
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.
Video Codecs Cheat Sheet — H.264 vs H.265 vs VP9 vs AV1 (2025)
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 Formats Cheat Sheet — MP3 vs AAC vs FLAC vs WAV vs OGG (2025)
Quick-reference comparison of audio formats: MP3, AAC, OGG, FLAC, WAV, Opus. Bitrate, quality, file size, compatibility, and streaming support at a glance.
Archive Formats Cheat Sheet — ZIP vs RAR vs 7Z vs TAR.GZ (2025)
Quick-reference comparison of archive formats: ZIP, RAR, 7Z, TAR.GZ, TAR.BZ2, TAR.XZ. Compression ratio, speed, encryption, OS support, and licensing.
File Size Limits Cheat Sheet — Email, Cloud, Social Media (2025)
Complete reference of file size limits across platforms: Gmail, Outlook, S3, GCS, Instagram, TikTok, YouTube, Discord, WhatsApp, Telegram. Updated for 2025.
MIME Types Cheat Sheet — Common Content-Types for Web Developers (2025)
Complete MIME type reference grouped by category with copy-paste snippets for Nginx, Apache .htaccess, and Express.js. Bookmark this for Content-Type configuration.
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.
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.
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 ZIP Extraction Errors — Corrupted Archives, Passwords, and Security
Fix ZIP extraction failures: corrupted archive, wrong password, path traversal (Zip Slip), encoding issues, and unsupported compression. With test ZIPs to reproduce.
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.
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.
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.
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.
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.
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.
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.
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.
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.