Guides
Converters solve the immediate problem; these guides explain the why behind it — what the formats actually are, which one a given job needs, and the traps people hit. Every guide pairs with tools on this site, so you can read the reasoning and do the job in the same place, without your files ever leaving your device.
How it works
What actually happens to your files here, and why that is different.
Certificates & keys
SSL/TLS formats, chains, CSRs, SSH keys — and the errors they cause.
Certificates & keysSSL certificate formats explained: PEM, DER, P7B, PFX and JKSEvery SSL/TLS certificate format explained — what each file holds, how to recognise it, which servers need which, and converting between them in your browser.Certificates & keysFix “certificate chain incomplete” and “unable to get local issuer certificate” errorsWhy a certificate works in Chrome but fails on phones, curl and Java — missing intermediates, wrong order, expired roots — and how to build a fullchain.pem.Certificates & keysCertificate signing requests explained: what a CSR contains and how to make one correctlyWhat’s inside a CSR, which subject fields still matter, why SANs replaced the Common Name, RSA vs ECDSA keys, and checking a request before you pay a CA.Certificates & keysSelf-signed certificates for local development: SANs, trust stores and the errors they causeWhen a self-signed certificate is right, making one browsers accept (SANs, not CN), where each OS keeps trusted certificates, and keeping it out of prod.Certificates & keysSSH keys explained: Ed25519 vs RSA, key formats, passphrases and converting between themHow SSH key authentication works, why Ed25519 is the default today, what OpenSSH and PEM keys look like, when to convert, and handling passphrases safely.Certificates & keysPFX and P12 files explained: what is inside, passwords, and getting PEM back outA PKCS#12 file holds your certificate, chain and private key behind one password. What that means, why IIS and Azure want it, and how to unpack or repack it.Certificates & keysJava keystores (JKS) demystified: aliases, keytool and moving keys to PFX or PEMWhat a JKS file is, why keytool has made PKCS#12 since Java 9, how aliases and its two passwords work, and extracting a certificate and key without a JDK.Certificates & keysYour SSL certificate expired: how to diagnose, renew and verify the fixNET::ERR_CERT_DATE_INVALID? Confirm what expired (leaf, intermediate or root), renew without downtime, install the right files and prove the fix from outside.
Images & photos
Formats, compression, metadata and the conversions everyone eventually needs.
Images & photosJPG, PNG, WebP or HEIC? Choosing the right image formatImage formats in plain language — lossy vs lossless, why screenshots hate JPG, what HEIC is, when WebP wins, and the right format for photos, logos and print.Images & photosHEIC explained: why iPhone photos will not open on Windows, and how to convert themWhat HEIC is, why Windows, Android and web forms reject it, the iPhone setting that stops it, and how to convert batches to JPG without uploading them.Images & photosCamera RAW files (CR2, NEF, ARW, DNG): what they are and how to get usable JPGsWhy a RAW file isn’t an image yet, what each camera brand’s extension means, what converting to JPG costs, and getting shareable photos without a RAW editor.Images & photosHow to compress images without visible quality loss: JPG quality, WebP and resizingWhere image bytes go, why resizing beats quality sliders, the JPG quality you can’t see, when WebP halves a file, and the settings for web, email and print.Images & photosWhat your photos reveal: EXIF, GPS and stripping metadata before you sharePhone photos carry location, time, device details and sometimes an uncropped thumbnail. What’s in there, which apps strip it, and how to remove it yourself.Images & photosFavicons and app icons: sizes, ICO vs PNG vs SVG, and the web manifestWhich icon files a modern site needs, why ICO still exists, the sizes browsers and home screens want, the web manifest, and making the set from one image.Images & photosAnnotating, watermarking and blurring images before they go publicRedact screenshots so hidden text can’t be recovered, watermark photos without ruining them, and add clear labels and arrows — all without uploading.
Video
Containers, codecs, compression and sharing video that actually plays.
VideoVideo containers vs codecs: why your MP4 won’t playMP4, MKV, MOV and WebM are containers; H.264, HEVC, VP9 and AV1 are the codecs inside. The difference explains most playback errors and slow conversions.VideoHow to compress a video for email, WhatsApp, Discord and Slack without wrecking itEach service’s real size limit, why resolution and length matter more than “quality”, bitrate maths you can do in your head, and a recipe to get under it.VideoMOV vs MP4: why iPhone videos misbehave on Windows and Android, and the fixMOV and MP4 are close cousins; the real problem is usually HEVC or Dolby Vision. How to tell, the iPhone settings that avoid it, and converting without loss.VideoMaking a good GIF from a video: frame rate, size, colours and when GIF is the wrong answerWhy GIFs are huge, the 256-colour limit and dithering, the frame rate and width that keep a clip small, and when a short MP4 or WebP beats a GIF.VideoScreen recording without installing anything: how browser recording works and how to get clean resultsHow a web page records your screen, what the permission grants, why the file is WebM, capturing system audio and a mic, and trimming and compressing it.VideoWebM vs MP4 for the web: codecs, browser support and which one to publishVP9 and AV1 in WebM versus H.264 in MP4: file size, browser and Safari support, hardware decoding on phones, and a decision rule for what to upload, embed or send.
Audio
Formats, bitrates and getting sound out of video.
AudioMP3, AAC (M4A), WAV, FLAC and OGG: which audio format to use for whatLossy vs lossless in plain terms, the bitrates where MP3 and AAC sound transparent, why WAV is huge, when FLAC is worth it, and which format to use where.AudioExtracting audio from video: lectures, podcasts and music without losing qualityCopying the audio track vs re-encoding it, which formats come out of which videos, trimming cleanly, and handling a two-hour lecture on an ordinary laptop.
Size, security, scanning and OCR.
PDFWhy PDFs get huge and how to shrink them: images, fonts, scans and compressionA 40-page contract shouldn’t be 60 MB. What really takes the space (images), what compression can recover, and meeting an upload limit with readable text.PDFPDF passwords and permissions: what protection really stops, and what it does notOpen vs owner passwords, why “no printing” is just a suggestion, what AES-256 really guarantees, and protecting or unlocking a PDF without uploading it.PDFOCR explained: turning scans and photos into searchable text, and getting accurate resultsHow OCR works, why a scanned PDF has no text to copy, what resolution and lighting do to accuracy, and how to OCR sensitive documents without uploading them.PDFMerging, splitting and reordering PDFs: workflows for contracts, scans and submissionsCombine PDFs in the right order, pull pages out of a long file, fix a scan that’s back to front, and number the pages — without broken or bloated results.PDFTurning phone photos into a clean PDF: scanning documents without a scannerLighting, angle and cropping tricks that make phone photos look scanned, combining pages into one small PDF, and making the text searchable with OCR.
Developer
Data formats, encodings, tokens, schedules and debugging real-time connections.
DeveloperJSON, YAML, TOML or XML? Choosing a config format and converting between themWhat JSON, YAML, TOML and XML are each good at, the YAML gotchas that broke real deployments, why TOML exists, and what gets lost converting between them.DeveloperCSV and JSON conversion pitfalls: delimiters, encodings, nesting and ExcelCSV has no real standard, so conversions break: quoted commas, semicolon locales, BOMs, leading zeros, Excel’s date rewrites, nested JSON. How to fix each.DeveloperJWTs explained: what is inside a token, how to decode one safely, and the mistakes that get apps breachedHeader, payload and signature; why anyone can read a JWT but not forge one; alg=none and key-confusion attacks; expiry, clock skew and handling tokens safely.DeveloperBase64 and URL encoding explained: what they are for, and when each is the wrong toolBase64 isn’t encryption and URL encoding isn’t HTML escaping. What each really does, the 33% size cost, the URL-safe alphabet, and bugs from mixing them.DeveloperCron expressions, decoded: the five fields, the traps, and how to test a scheduleCron’s five fields, the surprising OR between day-of-month and weekday, time zones, DST skips, six-field variants, and checking the next runs first.DeveloperHashing explained: MD5, SHA-1 and SHA-256, checksums, and why a hash is not encryptionWhat a hash guarantees, why MD5 and SHA-1 suit checksums but not security, how to verify a download, and why passwords need a slow, salted hash.DeveloperDebugging WebSocket, MQTT, STOMP, Socket.IO and SignalR connections from the browserWhy WebSocket and other real-time connections fail — mixed content, CORS, proxies dropping upgrades, idle timeouts — and how to isolate each from a browser.DeveloperDNS records explained: A, AAAA, CNAME, MX, TXT, NS and CAA, and why changes take timeWhat each DNS record does, the CNAME-at-apex rule, how TTLs cause “propagation”, the TXT records email needs, and how CAA limits who issues certificates.DeveloperUUID v4 vs v7: random or time-ordered, and which one your database wantsWhy random UUIDs fragment B-tree indexes, how v7 fixes that and stays hard to guess, what the bits encode, and when an auto-increment integer is still better.DeveloperRegular expressions for people who avoid them: the dozen constructs that cover most jobsCharacter classes, quantifiers, anchors, groups and alternation through patterns you’ll use — emails, dates, log lines — plus greedy and backtracking traps.DeveloperFrom a JSON sample to typed code: Go structs, GraphQL SDL, Mongoose schemas and SQL tablesTypes generated from a JSON sample are a first draft. What one sample can’t tell you about nulls, numbers, dates and arrays — and making types you can trust.DeveloperUnix timestamps and time zones: seconds vs milliseconds, UTC, DST and the 2038 problemSeconds vs milliseconds, what UTC buys you, the DST bugs that return every spring, ISO 8601 done right, and why 32-bit time runs out in 2038.DeveloperWeb fonts explained: TTF, OTF, WOFF and WOFF2, and how to ship fonts that load fastFont formats explained, why WOFF2 is all a modern site needs, subsetting, preloading, font-display, licensing traps, and converting desktop fonts for the web.
Everyday
File sharing, QR codes, archives, passwords and device checks.
EverydaySending large files between devices without the cloud: how peer-to-peer transfer worksWhy email stops at 25 MB, what cloud links do with your data, how browser-to-browser transfers work, and how to send multi-gigabyte files anywhere.EverydaySetting up a new computer: install all your apps at once on Windows, Mac and LinuxSet up a new PC or Mac in minutes: how winget, Homebrew and Flatpak install all your apps in one go, what can go wrong, and how to keep everything up to date.EverydayQR codes explained: error correction, sizes, what to encode, and printing them properlyHow a QR code stores data, why a link can make a small or a dense code, error-correction levels, print sizes and quiet zones, and the URL mistakes to avoid.EverydayTest your webcam, microphone and keyboard before a call, an exam or after a spillCheck your camera, mic and keyboard in a browser tab: what permission prompts mean, why one app sees the camera and another doesn’t, and finding dead keys.EverydayZIP, RAR, 7Z and TAR explained: how archives differ and how to open any of themWhy TAR isn’t compressed, what .tar.gz is, why RAR needs special software, when 7Z wins on size, and how to open any archive without installing anything.EverydayWhat makes a password strong: length, entropy, policies and generatorsPassword entropy in plain numbers, why length beats complexity rules, how attackers really crack passwords, and how a generator fits with a password manager.