Cyrillic Atbash cipher

This capability takes a non-empty text field, returns the transformed string with counts of mirrored Cyrillic letters and pass-through non-Cyrillic characters, and rejects empty input with a clear invalid_input error.

How Cyrillic Atbash works and what the response contains

Cyrillic Atbash mirrors each Russian letter by its index in the thirty-three-letter alphabet that places Ё after Е: uppercase А through Я maps to Я through А, and lowercase а through я follows the same reflection within the lower alphabet so case is preserved. The midpoint letter П maps to itself because the alphabet length is odd. Characters outside that Russian set—Latin A–Z, digits, punctuation, whitespace, emoji, and Ukrainian or other non-Russian Cyrillic letters—pass through unchanged so mixed messages keep their shape and spacing, while the response field non_cyrillic counts every code unit that was not mirrored. Send a JSON body with the required string field text set to any non-empty message; aliases input, value, and s are accepted when clients reuse older form names. Empty strings fail immediately with invalid_input because there is nothing meaningful to transform and the product promise is a real substitution result. On success the response includes result with the transformed text, method equal to atbash_cyrillic so downstream code can branch without sniffing shapes, length equal to the input character count, letters_mirrored counting how many Russian А–Я or а–я including Ё/ё units actually flipped, and non_cyrillic counting every other character. Identical inputs always produce identical JSON because the path is pure character arithmetic with no network, no random seed, and no wall clock. Use letters_mirrored and non_cyrillic together when you want to assert that mixed Latin-plus-Cyrillic strings still processed correctly without inventing a second mode field.

Encode, decode, validation rules, and common pitfalls

Missing text, non-string text, or an empty string all raise invalid_input and are not charged on the prepaid API. Whitespace-only strings that still have length greater than zero are accepted; only Russian Cyrillic letters mirror, so a string of spaces returns itself with letters_mirrored equal to zero and non_cyrillic equal to the length. Latin Atbash is a different product with a different SEO intent: do not expect English words inside text to flip A to Z here; they pass through and increase non_cyrillic.

API usage, pricing, classroom workflows, and practical limits

Call the free in-browser Cyrillic Atbash cipher for Russian puzzle drafting, Slavic-script monoalphabetic demos, lecture slides, and one-off checks without writing a one-liner in every language. Support playbooks can reverse lightly obfuscated ticket notes that staff intentionally wrote in Cyrillic Atbash. Pair with Latin Atbash or Base64 tools only when a later step needs a different alphabet—keep Cyrillic Atbash on its own landing so SEO intent stays sharp and does not cannibalize the English atbash cipher page. Use the prepaid KIT API when a backend, serverless function, tutoring platform, or SDK needs a stable contract under balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. A typical classroom workflow shows students that mirroring the Russian alphabet twice returns the original message, then contrasts that involution with a true keyed monoalphabetic cipher later in the syllabus, and uses non_cyrillic to discuss what happens when Latin brand names sit inside Russian copy. Puzzle sites can precompute Russian answers for display and reveal them on demand with the same endpoint. Authors shipping SDKs can map the result field straight into a copy button while method, letters_mirrored, and non_cyrillic make OpenAPI examples self-explanatory. Keep payloads to ordinary text sizes appropriate for a Worker isolate item call; this tool is for messages and snippets, not multi-megabyte binary blobs.