Introduction
Working with historical telegraph equipment or decoding old paper tape? The Baudot code, invented by Emile Baudot in the 1870s, was the first fixed-length character encoding for telegraphy. Each character is represented by 5 bits, with LTRS and FIGS shift characters to switch between letters and figures modes. This tool encodes text to Baudot code (ITA1) and decodes 5-bit Baudot sequences back to text, all in your browser.
What this tool does
- Encodes text into 5-bit Baudot code (ITA1) with space-separated binary output.
- Decodes 5-bit Baudot binary sequences back to text, handling LTRS/FIGS shift characters.
- Supports letters (A-Z), figures (digits, punctuation), and control characters (space, carriage return, line feed).
- Outputs binary in 5-bit groups separated by spaces for readability.
- Uses the original Baudot code (ITA1) assignments, not the later ITA2/Murray code.
- Processes all data locally with no server communication.
How this tool works
In Encode mode, type your text and the tool converts each character to its 5-bit Baudot code. The tool automatically inserts LTRS (11111) and FIGS (11011) shift characters when switching between letter and figure modes. The output is space-separated 5-bit groups. In Decode mode, paste a sequence of 5-bit codes (spaces are ignored) and the tool interprets them according to the current shift state. The Swap button toggles between modes.
How the Baudot code works
Jean-Maurice-Emile Baudot patented his telegraph system in 1874 and adapted it to a 5-bit code in 1876. The code was adopted as International Telegraph Alphabet No. 1 (ITA1) by the CCITT (now ITU-T). Baudot's innovation was the fixed-length encoding: every character takes exactly 5 bits, allowing automated printing telegraph machines to decode without human intervention. Five bits provide 32 combinations (2^5), which is enough for 26 letters but not for both letters and digits. Baudot solved this with a shift mechanism: two special codes (LTRS and FIGS) switch the receiver between letters mode and figures mode, doubling the effective character set. The operator presses a FIGS key to type numbers and punctuation, then an LTRS key to return to letters. The receiver remembers the current mode until a new shift arrives. Baudot's original code was designed for a 5-key keyboard operated with two fingers of the left hand and three of the right. The bit assignments were chosen to minimize mechanical wear on the keyboard. The term 'baud' (symbols per second) is named after Baudot. In 1901, Donald Murray modified Baudot's code to optimize for machine perforation rather than manual keyboard operation, rearranging character assignments to minimize the number of punches needed for frequently used letters. Murray's code was later standardized as ITA2 (International Telegraph Alphabet No. 2) in 1932 and became the standard teletypewriter code. ITA2 is commonly but incorrectly called 'Baudot code.' The original Baudot code (ITA1) and ITA2 are not mutually compatible. This tool implements the original Baudot code (ITA1). For ITA2 encoding, use the ITA2 Code tool on this site.
How to use this tool
- Select Encode mode and type your text. Letters, digits, and common punctuation are supported.
- The tool outputs 5-bit binary codes separated by spaces, with LTRS/FIGS shift codes inserted automatically.
- To decode, select Decode mode and paste a sequence of 5-bit codes. Spaces between codes are ignored.
- The tool interprets each 5-bit code according to the current LTRS or FIGS mode and outputs the decoded text.
- Use the Swap button to toggle between encoding and decoding.
Real-world examples
Encoding a simple message
Input: 'HELLO'. The tool starts with LTRS shift (11111), then encodes H (00101), E (10000), L (01001), L (01001), O (00011). Output: '11111 00101 10000 01001 01001 00011'.
Encoding mixed letters and numbers
Input: 'CODE 123'. The tool encodes C, O, D, E in LTRS mode, then space (00100), then FIGS shift (11011), then 1 (11101), 2 (11001), 3 (10000). The FIGS shift tells the receiver to interpret subsequent codes as figures.
Decoding a Baudot tape
Input: '11111 00101 10000 01001 01001 00011'. The tool reads the LTRS shift, then decodes each 5-bit code in letters mode to produce 'HELLO'. If the input starts with '11011' (FIGS), subsequent codes are interpreted as figures.
Comparison with similar methods
| Method | Complexity | Typical use |
|---|---|---|
| Baudot (ITA1) | 5-bit fixed-length, stateful shift | Historical telegraphy (1870s-1930s) |
| ITA2 (Murray) | 5-bit fixed-length, stateful shift | Teletypewriter, Telex (1930s-1960s) |
| ASCII | 7-bit fixed-length, no shift needed | Modern computing |
| Morse code | Variable-length, no shift | Early telegraphy, amateur radio |
Limitations or considerations
This tool implements the original Baudot code (ITA1), not the more common ITA2/Murray code. The two are not compatible. ITA1 was used primarily in France and the UK on Baudot's multiplex system and was never widely adopted for start-stop teleprinters. The character set is limited to uppercase letters, digits, and a few punctuation marks. Lowercase letters are not supported. The tool does not model start/stop bits, which were added later for asynchronous teleprinter communication. Some ITA1 code assignments varied between national implementations.
Frequently asked questions
What is the difference between Baudot code and ITA2?
Baudot code (ITA1) was Emile Baudot's original 1870s encoding, designed for a 5-key manual keyboard. ITA2 (International Telegraph Alphabet No. 2) was standardized in 1932 based on Donald Murray's 1901 modification, designed for machine perforation. They use different character assignments for the same 5-bit codes. ITA2 became the standard for teletypewriter and Telex service.
Why does the code use shift characters?
Five bits provide only 32 combinations, which is enough for 26 letters plus control characters but not for both letters and digits. The LTRS and FIGS shift characters double the effective character set by switching between two modes. The receiver remembers the current mode until a new shift code arrives.
What is the baud rate?
The baud, named after Emile Baudot, measures symbol rate (symbols per second). Early Baudot equipment operated at around 30 words per minute, approximately 25 baud. Later teleprinters using ITA2 operated at 50, 75, or 110 baud. The term 'baud' is often confused with bits per second, but they are equivalent only when each symbol carries one bit.
Can I use this tool to decode historical paper tapes?
Yes, if the tape uses ITA1 code. Most surviving paper tapes use ITA2, not ITA1. For ITA2 tapes, use the ITA2 Code tool on this site. You need to read the 5-bit patterns from the tape and enter them as binary strings.
Conclusion
The Baudot code represents a milestone in telecommunications history: the first fixed-length character encoding for automated telegraphy. This tool implements the original ITA1 code assignments. For the more common ITA2/Murray code used in teletypewriter systems, use the ITA2 Code tool on this site. Check out the related Morse code translator and ITA2 code tools for historical encoding comparison.