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UnicodeWorks.com

Substitution Cipher Decoder

Decode monoalphabetic substitution ciphers with frequency aids.

How it works

  • Paste ciphertext, inspect its letter-frequency counts and enter a 26-letter plaintext mapping for ciphertext A–Z.
  • The decoded preview updates as the mapping changes.

Assumptions and limitations

  • The tool assists manual monoalphabetic substitution analysis; it does not automatically solve arbitrary substitution ciphers.
  • A valid mapping must contain each A–Z letter exactly once.

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