Text
Cipher Identifiers
These websites can help you identify the type of cipher in an unknown text. They are not always 100% accurate, and you may have to test some of the top recommendations.
https://www.dcode.fr/cipher-identifier
https://bionsgadgets.appspot.com/gadget_forms/refscore_extended.html
https://www.boxentriq.com/code-breaking/cipher-identifier
Multitool
These sites have a variety of tools to handle multiple different ciphers.
https://www.dcode.fr/en
Easier for beginners, as most tools have a method to work out the key automatically.
https://cyberchef.org/Most tools require you to input the valid key, rather that being able to do it automatically. This requires more practice to use, but is better at chaining together ciphers in long cipherstacks.
File Hex Editors
The following can be used to view and manually edit the raw contents of a file.
https://hexed.it/
https://www.onlinehexeditor.com/
Monoalphabetic Substitution
These pages are useful for decoding standard substitution ciphers, also known as cryptograms.
https://quipqiup.com/
Has various modes of solving a substitution.
https://www.boxentriq.com/code-breaking/cryptogramContains explanation of the cipher and allows manual solving.
https://www.guballa.de/substitution-solverMulti-language: supports English, German, Spanish, French, Dutch & Portuguese.
Vigenère
The following websites are useful at decoding polyalphabetic Vigenère ciphers automatically. A tabula recta can be useful if you want to understand the process.
Vigenère can be tricky sometimes, so it may be worth trying all the tools here.
https://www.boxentriq.com/code-breaking/vigenere-cipher
Uses a dictionary attack, which can help if the key is a word.
https://www.dcode.fr/vigenere-cipherAllows for a lot of customization, and can decode automatically.
https://www.guballa.de/vigenere-solverMulti-language: supports English, German, Spanish, French, Dutch & Portuguese.
https://f00l.de/hacking/vigenere.phpCan calculate the period of the key.
Caesar
The links below are useful for solving Caesar and other rotation-based ciphers.
https://a4x.me/tools/text/
http://theblob.org/rot.cgi
https://multidec.web-lab.at/mr.php
https://planetcalc.com/1434/
Multi-language: supports English, French, Portuguese, Russian & Spanish.
Base64 & Variants
These are useful for decoding base64-like texts, and include modern symmetric encryption capabilities, such as with AES.
https://corgi.rip/dive
Dumpster Diver (random b64 looking text brute forcer)
https://aesencryption.net/Aesencryption.net (AES)
https://www.online-toolz.com/tools/text-encryption-decryption.php/Stupid Base64 aka SB64 (AES)
https://codebeautify.org/encrypt-decryptCodebautify (Arcfour)
https://encipher.it/encipher.it (AES PGP)
https://pteo.paranoiaworks.mobi/Paranoiaworks (AES EAX)
https://www.samltool.com/decode.phpsamltool (XML)
https://decipher.wiki/aes-decryptionaesdecryption (AES)
https://www.samltool.com/decode.phpsamltool (base64 + decompression)
https://asecuritysite.com/encryption/ferdecodegAAAAA AES, aka Ferdecode
https://www.browserling.com/tools/aes-encryptbrowserling (salted openssl)
https://www.devglan.com/online-tools/text-encryption-decryptionDevglan (AES)
https://www.invertexto.com/texto-criptografadoinvertexto (AES)
https://encode-decode.com/aes256-encrypt-online/encode-decode (AES)
https://anycript.com/anycript (AES)
https://web.archive.org/web/20220915201921/https://cryptoji.com/cryptoi (AES presented in emojis)
Miscellaneous
These tools have a variety of purposes, and their capabilities are listed in the description below each link.
https://www.dcode.fr/alphabetic-transcription
N-gram transcription: transcribes text in any group length or from unicode symbols.
https://www.soscisurvey.de/tools/view-chars.phpAllows you to view non-printable characters.
https://www.onelook.com/Word finder: for example, ??i???n??e => chimpanzee.
https://a4x.me/tools/link/Link identifier: for example, oHg5SJYRHA0 => https://www.youtube.com/watch?v=oHg5SJYRHA0.
https://cyber.meme.tips/xlate/shifts.htmlByte shift: allows you to view all byte shifts and all constant XOR’s.
https://www.browserling.com/tools/text-invert-caseCasing inverter.
https://onlinetexttools.com/remove-all-whitespace-from-textRemoves spaces and other whitespaces from text.
https://norvig.com/mayzner.htmlEnglish monogram language frequencies.
https://tio.run/#Esolangs decoder.
https://www.mobilefish.com/services/big_number/big_number.phpLarge number converter: allows binary, hex, decimal & base64 conversion.
https://330k.github.io/misc_tools/unicode_steganography.htmlInvisible characters in text decoder.
https://www.dorksearch.com/Dork search tool.
https://osintframework.com/Osint framework.
https://online-free-tools.com/en/youtube_video_tags_extract_urlYoutube video tag extractor.