Decode Morse code without spaces

1. 1

   Paste the dots and dashes into the box, or tap an example. Look-alike dots and dashes (· • − —) and underscores read as dots and dashes.

2. 2

   Keep any gap you are sure of. A space ends a letter, and a slash, a bar or three spaces end a word, so the decoder never reads across them.

3. 3

   Read the likeliest reading at the top, with each letter over its code. Tap another reading in the list to see its split.

4. 4

   Copy the text, or copy the reading as spaced Morse and press Play to hear it with the gaps put back, at 18 WPM.

5. 5

   Written the other way round, or in 0 and 1? Turn on Swap dots and dashes, or type the two symbols under Other symbols.

Each message below was sent with its gaps removed, then pasted into the decoder. The table shows how many ways it splits into letters, the top three readings, and where the message that was really sent came in.

Common words come through first. MORSE CODE run together is the exception worth knowing: TONNES CODE uses words that are more common in the word list, so it ranks first and MORSE CODE comes in at number 2.

With its letter gaps kept, MORSE reads first. When a reading looks wrong, check the list under it, and add any gap you are sure of.

Letters that make no word from the list are shown dotted, as loose letters, so you can see which part of a reading is a word and which is only letters. Once you have chosen a reading and put its gaps back, the tool for decoding spaced Morse into English reads it, plays it and shows it letter by letter.

In Morse code, only silence marks where a letter ends: a gap three dots long between letters, seven between words. Many letters are other letters joined together. E is one dot, I is two, S three and H four, so four dots in a row, written .... with no gaps, read 8 ways:

• EEEE
• EEI
• EIE
• ES
• H
• IEE
• II
• SE

The distress call shows it best. SOS keyed as one signal, with no gaps, is ...---..., nine symbols that split into letters 192 ways.

SOS is one of them, and so are EEETTTEEE, VTB, IJS, SMB, VMS. The decoder still puts SOS first, because it is a word in the list and the others are not.

The count grows fast with length. A run of dots, which can only be E, I, S or H, splits like this:

The letters that sound alike are the same ones that run together. The drill for letters that run together in Morse trains your ear on them, and the Morse code tree shows how each letter grows out of a shorter one.

The decoder never lists every split; there are far too many. It searches for the cheapest ones, the way a computer splits text written without spaces into words:

1. 1

   Every word it knows comes from a list of 19,991 common English words, ordered by how often each appears in English Wikipedia. A common word costs little, a rare one more.

2. 2

   Letters that make no listed word still count, but cost much more, the rarer letters most. So a reading made of words always beats the same symbols read as loose letters.

3. 3

   Working back from the end, it keeps only the cheapest readings at each point, which keeps the search quick even when the splits number in the billions or more.

4. 4

   It reads the letters A to Z only. Digits take five symbols each and would add splits without making any reading likelier.

It reads up to 80 dots and dashes and lists up to 20 readings, so it stays quick on a phone. A longer message is cut at 80, and the tool says so: split it at a gap you are sure of and read it in parts. The word list loads only when the tool opens, and everything runs in your browser.

The ranking knows words, not your message. Names, call signs and abbreviations may be missing from the list, and two short common words can beat the one long word you meant. Treat the first reading as a lead, not the answer.

1. 1

   Keep the Morse code alphabet chart next to you, or open Letters by length under the tool: the letters sorted by how many symbols they take.

2. 2

   Start at the left. Try the longest letter that fits the symbols, write it down and move on.

3. 3

   When what is left can’t make a word, step back and try a shorter letter where you last had a choice.

4. 4

   Look for common words and endings (THE, AND, ING) and mark every split you are sure of with a space.

To make a puzzle of your own, switch the tool to Text to Morse. It runs your message together and lists what else the same signal could say, so you can check it is hard enough, or not too hard.