SelfDevKit Blog

SQL CASE explained with tested output: simple vs searched syntax, NULL traps, conditional aggregation, UPDATE pitfalls, and dialect differences.

LEFT JOIN SQL explained with tested output: ON vs WHERE, anti-joins, COUNT and SUM fan-out, chained joins, and dialect differences.

Convert FLAC to MP3 without losing track totals, lyrics, or album art. Tested ffmpeg commands, a tag fix script, and a library batch script.

CTE SQL explained with tested output: WITH syntax, recursive CTEs, cycle detection, materialization, data-modifying CTEs, and dialect gaps.

Get a sample PDF for testing, then go further: 11 edge-case PDFs (encrypted, truncated, scanned) run through 5 parsers, plus a script to make them.

A SQL cheat sheet with core syntax, tested NULL traps, and a dialect table for MySQL, PostgreSQL, SQL Server, and SQLite.

Convert WebM to MP4 with tested ffmpeg commands: when remuxing works, why VP8 needs a re-encode, and fixes for odd sizes, missing durations, alpha.

SQL window functions explained with tested output: ROW_NUMBER, RANK, LAG, running totals, frame traps, QUALIFY, and dialect support.

Convert GIF to PNG with zero pixel changes, keep it smaller than the GIF, and extract animated frames without cropping. Tested commands.

Convert WAV to MP3 with the right bitrate. Measured file sizes, the silent 96 kHz and 5.1 changes, clipping fixes, and MP3 back to WAV.

Convert MKV to MP4 losslessly in seconds. Tested ffmpeg commands that keep every audio and subtitle track, plus fixes for PGS subs and HEVC.

UTC to EST means subtracting 5 hours, or 4 during daylight saving (EDT). Conversion chart, 2026-2027 switch dates, and code that gets DST right.

Convert MOV to MP4 with a lossless remux in seconds, or re-encode when needed. Tested fixes for iPhone HDR, ProRes, audio tracks and GPS data.

Convert WebP to JPG offline, in the terminal, or in code. Tests show why transparent areas turn black or garbled, and which JPG quality to pick.

Convert WebP to PNG offline, in the terminal, or in code, and see what the conversion does to file size, animation, color profiles and EXIF.

Every SSH key generator is really a random number generator. Compare ssh-keygen, PuTTYgen, browser and cloud tools, and verify the key you got.

A regex cheat sheet with syntax tables, flags, and the portability gaps most references skip: what breaks in Go, Python, grep, and JSON strings.

How to use an API key generator safely: entropy sizing, output formats, one-liners in four languages, and how to audit a generator before you trust it.

Convert Unix timestamp values correctly by identifying the unit and epoch first, then converting inside SQL, log tools, and spreadsheets.

A timestamp unix converter is easy to find and easy to trust. See how five tools disagree on one input, plus a test suite to check yours.

Learn how to generate an API key in Stripe, GitHub, and Google Cloud, plus how to issue, hash, and verify keys for an API you built yourself.

Crontab generate tools stop at five fields. Learn to generate the whole cron line: absolute paths, logging, locking, and jitter.

Hex to RGB charts for CSS colors and greys, mental math you can do without a tool, and why OKLCH palettes broke the exact conversion.

Convert hex to RGB color values correctly: the math, shorthand and alpha rules, parser code, and the platform gotchas that break conversions.

Convert markdown to HTML the right way: the full element mapping, why output is a fragment not a page, and the gotchas that break conversions.

See a real API key example from Stripe, GitHub, AWS, and Google, plus safe sample keys for docs and tests that will not trip secret scanners.

Date to timestamp unix conversion is not symmetric. Learn the timezone each language assumes, the DST traps, and code for 8 platforms.

Crontab explained: what every flag does, how crontab -e really works, which flags change meaning between systems, and how to avoid wiping your jobs.

x-api-key is the de facto header for API key auth. How to send it, validate it, fix CORS and AWS 403 errors, and why header casing bites you.

Cron and crontab explained: what the daemon does, where crontab files live on disk, the sixth field, and the gotchas that make jobs fail silently.

Convert JSON to CSV without corrupting your data: flattening strategies, RFC 4180 escaping, code in Python, Node and jq, plus CSV injection risks.

A SQL query formatter turns logged, ORM-generated, one-line SQL into readable queries. Here is the full cleanup workflow, from log line to EXPLAIN.

Formatter SQL explained: how SQL formatters parse queries, why dialect matters, and where they break on templates, placeholders, and embedded SQL.

Learn what a diff checker is, the different types, how they work, and how to compare text and code privately offline.

Learn how to generate an SSH key with ssh-keygen, choose ed25519 vs RSA, add a passphrase, and keep your private key off untrusted servers.

What is an API key? A plain-English guide to how API keys work, what they look like, how to send them, and how to generate and store them securely.

What crontab guru is, how its cron editor works, and how to read any cron expression yourself, plus a private offline alternative.

Learn how to test regex the right way: write test cases, handle engine flavor differences, catch catastrophic backtracking, and debug patterns offline.

Use an RSA key generator to create public and private key pairs in PEM format. Learn key sizes, formats, and why generating keys offline matters.

A markdown editor online lets you write and preview markdown in real time. Compare the best editors, learn the syntax, and keep drafts private.

Learn how a markdown viewer online renders your text, why GFM previews differ, and how to preview markdown privately without a browser tab.

Copy ready-made lorem ipsum paragraphs, learn how long each one is, and test multi-paragraph typography. Offline generator for developers.

Generate GUIDs online, learn the .NET format specifiers, and see why an offline GUID generator keeps your identifiers off unknown servers.

Learn how to HTML encode special characters, why entity encoding stops XSS, and how it differs from URL encoding. With code examples and an offline tool.

A word counter online tallies words and characters instantly. Compare the top online tools and learn when an offline counter keeps your text private.

Learn how an image resizer works, which resampling algorithm to pick, and how to resize images offline without uploading private files to a server.

Convert image to base64 with data URIs, code examples in JS, Python, and Node, plus build-tool automation for CSS and HTML embedding.

Learn how a SHA256 generator works, generate hashes in JS, Python, Go, and the CLI, and fix the reasons two SHA-256 hashes never match.

A word counter for developers. Count words, characters, and bytes in your text. Learn counting techniques and why offline tools keep content private.

Use a JSON formatter online to beautify and validate JSON data. Learn the best tools, privacy risks, and code examples.

Lorem ipsum text explained: its origin from Cicero, what the Latin actually means, ready-to-copy blocks, and developer use cases.

Learn how to text compare two documents using diff tools, CLI commands, and code examples across languages.

Use a JSON validator to find syntax errors fast. Fix common mistakes and validate programmatically in JS and Python.

Learn how to JSON compare with code examples, CLI tools, and visual diff viewers to find every difference fast.

Learn how to use a JSON viewer to explore nested data, debug API responses, and navigate large JSON files with tree view.

Learn how to use a base64 encoder in JavaScript, Python, Go, Rust, and the command line. Covers UTF-8 pitfalls, URL-safe encoding, and output size.

Use a lorem ipsum generator to create placeholder text for layouts, testing, and prototyping. Code examples, use cases, and offline tools.

Learn how to base64 decode strings in every major language, the CLI, and desktop tools. Covers troubleshooting, URL-safe variants, and privacy.

Learn cron syntax, build expressions with a crontab generator, and debug cron jobs that fail silently.

Use this unix timestamp converter guide with code examples in 6 languages, seconds vs milliseconds reference, and Y2038 explained.

Compare the best SQL formatter online tools and learn when offline formatting is the safer, faster choice for developers.

Learn how to use a code diff checker to compare files, read unified diff output, and spot changes fast.

Convert JSON to TypeScript interfaces automatically. Learn manual and automated approaches with real code examples.

Use an RGB color picker to find exact color values, convert formats, and write modern CSS with confidence.

An image converter transforms files between PNG, JPG, WebP, GIF, and TIFF. Learn each format and why offline conversion matters.

Learn how to format SQL queries for readability. Covers style conventions, code examples, and offline formatting tools.

Learn how a URL parser breaks URLs into components like protocol, host, path, and query strings for faster debugging.

Learn how to use an HTML formatter to beautify messy markup, minify for production, and validate your code offline.

Generate UUIDs and unique IDs for your projects. Learn which version to use, how they work, and why UUID v7 is replacing v4.

Use a hex color picker to find exact color codes, convert between formats, and check WCAG contrast.

Learn how to decode JWT tokens using desktop tools, command-line one-liners, and code in JavaScript, Python, and Go.

Learn how to convert base64 to image and back with code examples in JavaScript, Python, and Node.js, plus fixes for the most common decoding errors.

Learn how to generate a JWT secret key that actually meets RFC 7518 requirements, plus the format decisions developers always get wrong.

Learn every approach to JSON to Dart conversion: manual fromJson, json_serializable, and freezed, with real-world nested object examples.

Learn how to JSON minify for production, cut file sizes by up to 40%, and avoid the privacy risks of pasting sensitive data into online tools.

Learn how to unescape JSON strings in Python, JavaScript, and Go with code examples and debugging tips.

Learn how I use SelfDevKit to build native iOS applications like FeelClose, a long-distance couples app. From debugging Supabase APIs to decoding JWTs, see the developer tools that power mobile development.

Learn how I use SelfDevKit to build production services like Is It Visible, a mountain visibility forecasting platform. From JSON debugging to URL encoding, see the developer tools that power real projects.

Master regex with this comprehensive regex tester guide. Learn regex syntax, common patterns for validation, capture groups, and how to test expressions effectively with real-world examples.

Learn how hash generators work and when to use MD5, SHA256, SHA512, or BLAKE. Understand hashing for file integrity, password security, and API authentication with practical examples.

Learn how to base64 encode and decode text and images. Understand data URIs, when to use Base64, and how to convert images to Base64 strings for HTML, CSS, and APIs.

Learn how to generate truly secure passwords in 2025. Understand password entropy, strength analysis, and why offline generators are the only safe choice for your credentials.

Learn how to decode, validate, and debug JWT tokens securely. Understand JWT structure, algorithms, claims, and why offline decoders protect your authentication secrets.

Learn how to format, view, validate, and debug JSON data efficiently. Discover the best JSON tools for developers and why offline formatters protect your sensitive API data.

Discover why privacy-focused, offline developer tools are essential in 2025. Learn how local processing protects your API keys, JWT tokens, and sensitive data while delivering instant performance.

Master SelfDevKit from installation to advanced workflows. Learn how to use JSON tools, JWT decoder, ID generators, and 50+ developer utilities to boost your productivity while keeping your data completely private.