Tools / Cipher Identifier
Cipher Identifier & Auto-Decoder
Paste a string and this tool tries every common decoder (base64, hex, Morse, ROT/Caesar, Atbash, Bacon, binary, decimal codepoints, URL-encoded), scores each result by how English it looks, and shows the top hits. Inspired by CyberChef’s Magic recipe but focused on the encodings that show up in CTF challenges.
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Decoder candidates (sorted by English-likeness)
How the ranking works
Each candidate is scored on (1) how closely its letter frequency matches English (chi-square fit), (2) how many common English words appear, and (3) whether it contains a flag-shaped string like picoCTF{...}. High-confidence hits glow green; weaker guesses are shown for completeness so you can spot patterns the scorer missed (numeric flags, leetspeak, language other than English).
For chained encodings (base64 wrapping hex wrapping ROT13, etc.) the tool tries up to two passes automatically. If nothing scores above the threshold, the input is likely keyed (Vigenere, RSA, AES) - open the Vigenere, RSA Calculator, or AES Decryptor and supply the key. Substitution ciphers are best attacked with the Frequency Analysis tool.
Challenges that use this tool
- Hidden Cipher 1picoCTF 2026 · Reverse Engineering · Medium
- Hidden Cipher 2picoCTF 2026 · Reverse Engineering · Medium
- interencdecpicoCTF 2024 · Cryptography · Easy
- repetitionspicoCTF 2023 · General Skills · Easy
- rotationpicoCTF 2023 · Cryptography · Medium
- basic-mod1picoCTF 2022 · Cryptography · Medium
- basic-mod2picoCTF 2022 · Cryptography · Medium
- credstuffpicoCTF 2022 · Cryptography · Medium
- morse-codepicoCTF 2022 · Cryptography · Medium
- Mod 26picoCTF 2021 · Cryptography · Easy
- 13picoCTF 2019 · Cryptography · Easy
- caesarpicoCTF 2019 · Cryptography · Medium
Browse the full challenge library for 17 more.
Guides that use this tool
- What Is picoCTF? Who Built It, Why, and What It Actually TeachespicoCTF is Carnegie Mellon's free hacking competition, started in 2013 by CMU's own CTF team. Who built it, why, and what its own research changed.
- Esoteric Languages in CTF: Recognising Code That Does Not Look Like CodeIdentify and run the esolangs that show up in CTF: Brainfuck, Whitespace, Rockstar, Befunge, Piet, JSFuck and Redcode, with a fingerprint table and an interpreter.
- picoCTF 2026: Every Challenge, Sorted by What It Actually TeachesA category-by-category guide to the 70 picoCTF 2026 challenges: what changed this season, which ones teach the most, and a walkthrough link for every single one.
- sqlmap for CTF: Every Flag That Matters, and What to Do When It Finds NothingA practical sqlmap workflow for CTF: request files, level and risk, technique selection, tamper scripts, second-order injection, and the failure checklist.
- Windows Forensics for CTF: Event Logs, Registry Hives, BitLocker, and SMBWork Windows artifacts from Linux: parse .evtx event logs, read registry hives offline, crack and mount BitLocker volumes, enumerate SMB shares, write YARA rules.
- Side-Channel Attacks for CTF: Timing, Power, Compression, and Cache OraclesRecover secrets from what a program leaks rather than what it outputs: timing leaks, correlation power analysis, compression oracles, and cache eviction channels.
Tools that pair with this one
- Frequency AnalysisAnalyze letter frequencies in a substitution cipher and interactively build the decryption mapping with auto-filled guesses.
- ROT / Caesar CipherDecode Caesar-shifted and ROT-encoded text. Drag the shift slider or scan all 26 rotations at once.
- Vigenère CipherEncrypt or decrypt text with the Vigenère polyalphabetic substitution cipher using a keyword.
- Recipe ChainStack decoders into a pipeline: Base64, hex, ROT, XOR, Morse, URL, Atbash, Vigenère, and more. Magic mode auto-discovers the chain. Bookmark the URL to save it.
Or browse all 40 CTF tools.