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 JKSA practical guide to every SSL/TLS certificate format — what each file contains, how to recognise it, which servers need which, and how to convert 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. How to diagnose each case and build a correct fullchain.pem.Certificates & keysCertificate signing requests explained: what a CSR contains and how to make one correctlyWhat is inside a CSR, which subject fields still matter, why SANs replaced the Common Name, RSA vs ECDSA key choices, and how to check a request before you pay a certificate authority for it.Certificates & keysSelf-signed certificates for local development: SANs, trust stores and the errors they causeWhen a self-signed certificate is the right tool, how to make one browsers accept (SANs, not CN), where each operating system keeps its trust store, and how to keep dev certificates out of production.Certificates & keysSSH keys explained: Ed25519 vs RSA, key formats, passphrases and converting between themHow SSH key authentication works, why Ed25519 is the default choice today, what the OpenSSH and PEM key formats look like, when you need to convert, and how to handle passphrases safely.Certificates & keysPFX and P12 files explained: what is inside, passwords, and getting PEM back outPKCS#12 carries your certificate, chain and private key in one password-protected file. Learn what that means for security, why IIS and Azure want it, and how to unpack, repack and re-password one.Certificates & keysJava keystores (JKS) demystified: aliases, keytool and moving keys to PFX or PEMWhat a JKS file is, why keytool has quietly been making PKCS#12 since Java 9, how aliases and two passwords work, and how to get a certificate and key out of a keystore without installing a JDK.Certificates & keysYour SSL certificate expired: how to diagnose, renew and verify the fixThe browser says NET::ERR_CERT_DATE_INVALID. Here is how to confirm what actually 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 formatA plain-language guide to image formats — lossy vs lossless, why screenshots hate JPG, what HEIC is, when WebP wins, and which format to pick for photos, logos, web pages and printing.Images & photosHEIC explained: why iPhone photos will not open on Windows, and how to convert themWhat HEIC/HEIF is, why Apple adopted it, why Windows, Android and many web forms reject it, the settings that stop your iPhone producing 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 is not an image yet, what each brand’s extension means, what you lose and gain converting to JPG, and how to get shareable photos out of a camera card without a desktop RAW editor.Images & photosHow to compress images without visible quality loss: JPG quality, WebP and resizingWhere image bytes actually go, why resizing beats quality sliders, the JPG quality range that is invisible in practice, when WebP halves a file for free, and the settings to use for web, email and print.Images & photosWhat your photos reveal: EXIF, GPS and stripping metadata before you shareEvery phone photo carries location, time, device and sometimes a thumbnail of the uncropped original. Learn what is in there, which apps strip it and which do not, 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 really needs, why ICO still exists, the sizes browsers and home screens ask for, how the web manifest fits in, and how to produce the whole set from one source image.Images & photosAnnotating, watermarking and blurring images before they go publicHow to redact screenshots so the hidden text cannot be recovered, watermark photos without ruining them, add readable labels and arrows, and crop out what should not be there — 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 boxes; H.264, HEVC, VP9 and AV1 are what is inside. Understanding the difference explains almost every playback error — and why some conversions take seconds while others take an hour.VideoHow to compress a video for email, WhatsApp, Discord and Slack without wrecking itThe real size limits of each service, why resolution and length matter more than “quality”, bitrate maths you can do in your head, and a repeatable recipe for getting a clip under the limit.VideoMOV vs MP4: why iPhone videos misbehave on Windows and Android, and the fixMOV and MP4 are close cousins, so the real culprit is usually HEVC or a Dolby Vision profile. Learn how to tell, the iPhone settings that avoid it, and the conversion that keeps quality intact.VideoMaking a good GIF from a video: frame rate, size, colours and when GIF is the wrong answerWhy GIFs are enormous, the 256-colour limit and dithering, the frame rate and width that keep a clip under a few megabytes, and when a short MP4 or WebP beats a GIF outright.VideoScreen recording without installing anything: how browser recording works and how to get clean resultsHow a web page can record your screen, what the permission prompt actually grants, why the output is WebM, how to capture system audio and a microphone, and how to trim and compress the result.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 become transparent, why WAV is huge, when FLAC is worth it, and which format each device, platform and use case actually wants.AudioExtracting audio from video: lectures, podcasts and music without losing qualityThe difference between copying the audio track and re-encoding it, which formats come out of which videos, how to trim the result cleanly, and how to do all of it for a two-hour lecture on a laptop.
Size, security, scanning and OCR.
PDFWhy PDFs get huge and how to shrink them: images, fonts, scans and compressionA 40-page contract should not be 60 MB. Learn what actually takes the space (almost always images), what compression can and cannot recover, and how to hit an upload limit without turning text to mush.PDFPDF passwords and permissions: what protection really stops, and what it does notOpen passwords versus owner passwords, why “no printing” is a suggestion, what AES-256 encryption actually guarantees, and how to protect or unprotect a document without sending it anywhere.PDFOCR explained: turning scans and photos into searchable text, and getting accurate resultsHow optical character recognition 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 submissionsHow to combine documents in the right order, pull specific pages out of a long file, fix a scan with pages back to front, and number the result — with the traps that produce broken or bloated PDFs.PDFTurning phone photos into a clean PDF: scanning documents without a scannerLighting, angle and cropping tricks that make a phone photo look scanned, how to combine pages into one PDF, keeping the file small, 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 each format is good at, the YAML gotchas that have taken down real deployments, why TOML exists, when XML is still the right call, and what gets lost converting between them.DeveloperCSV and JSON conversion pitfalls: delimiters, encodings, nesting and ExcelCSV has no real standard, which is why conversions break: quoted commas, semicolon locales, BOMs, leading zeros, dates Excel rewrites, and nested JSON that has no flat shape. How to handle 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; the alg=none and key-confusion attacks; expiry and clock skew; and why you should never paste a live token into a random website.DeveloperBase64 and URL encoding explained: what they are for, and when each is the wrong toolBase64 is not encryption and URL encoding is not escaping for HTML. Learn what each transformation actually does, the 33% size cost, the URL-safe alphabet, data: URLs, and the bugs from mixing them up.DeveloperCron expressions, decoded: the five fields, the traps, and how to test a scheduleMinute, hour, day, month, weekday — and the surprising OR between day-of-month and day-of-week. Time zones, DST skips, the non-standard six-field variants, and how to check the next runs before deploying.DeveloperHashing explained: MD5, SHA-1 and SHA-256, checksums, and why a hash is not encryptionWhat a hash function guarantees, why MD5 and SHA-1 are fine for checksums but not security, how to verify a download, why passwords need a slow hash and a salt, and how hashes show up in Git and JWTs.DeveloperDebugging WebSocket, MQTT, STOMP, Socket.IO and SignalR connections from the browserA field guide to why real-time connections fail: mixed content, CORS on the handshake, proxies that drop upgrades, idle timeouts, protocol mismatches, and how to isolate each with a browser-side client.DeveloperDNS records explained: A, AAAA, CNAME, MX, TXT, NS and CAA, and why changes take timeWhat each record type does, the CNAME-at-apex rule, how TTL and caching cause “propagation”, the TXT records that make email deliverable, and how CAA controls who can issue your certificates.DeveloperUUID v4 vs v7: random or time-ordered, and which one your database wantsWhy random UUIDs fragment B-tree indexes, how v7 fixes it while staying unguessable enough, what the bits actually encode, and when an auto-increment integer is still the better key.DeveloperRegular expressions for people who avoid them: the dozen constructs that cover most jobsCharacter classes, quantifiers, anchors, groups and alternation explained with the patterns you actually need — emails, dates, log lines — plus the greedy-matching and catastrophic-backtracking traps.DeveloperFrom a JSON sample to typed code: Go structs, GraphQL SDL, Mongoose schemas and SQL tablesGenerated types are a first draft, not a contract. What a single sample can and cannot tell you about nullability, numbers, dates and arrays, and how to turn generator output into schemas you can trust.DeveloperUnix timestamps and time zones: seconds vs milliseconds, UTC, DST and the 2038 problemWhy 1700000000 and 1700000000000 are the same instant in different units, what “UTC” buys you, the DST bugs that recur 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 fastWhat each font format is, why WOFF2 is the only one a modern site needs, subsetting and preloading, font-display choices, licensing pitfalls, and how to convert a desktop font 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 caps at 25 MB, what cloud links really do with your data, how a browser-to-browser WebRTC transfer works, when it needs a relay, and how to move multi-gigabyte files across a room or a continent.EverydayQR codes explained: error correction, sizes, what to encode, and printing them properlyHow a QR code stores data, why the same link can be a small or a dense code, the four error-correction levels, minimum print sizes and quiet zones, and the URL mistakes that make codes fail in the field.EverydayTest your webcam, microphone and keyboard before a call, an exam or after a spillHow to check camera, mic and keys in a browser tab, what the permission prompts mean, why one app sees the camera and another does not, and how to diagnose stuck, dead or ghosting keys.EverydayZIP, RAR, 7Z and TAR explained: how archives differ and how to open any of themWhy TAR is not compressed, what .tar.gz really is, why RAR needs special software, when 7Z wins on size, encrypted archives, and how to extract any of them without installing anything.EverydayWhat makes a password strong: length, entropy, policies and generatorsEntropy in plain numbers, why length beats complexity rules, how attackers actually crack passwords, what a database or service password should look like, and where a generator fits with a password manager.