Codon Translator
Paste an mRNA transcript or a DNA coding strand and this tool reads it as non-overlapping triplets, mapping each codon to its amino acid with the standard genetic code (NCBI table 1). You get the protein as a one-letter string plus a row-by-row table of codon, three-letter code, one-letter code and full name. Whitespace and line breaks are stripped, so you can paste straight from a FASTA line or a textbook.
How to translate codons
- Paste or type your sequence into the 'mRNA or DNA sequence' box using the letters A, C, G, U (and T for DNA).
- Tick 'Input is DNA (read T as U)' if you pasted a DNA coding strand rather than mRNA.
- Leave 'Stop at first stop codon' on to end at the first stop, or clear it to translate every full triplet.
- Read the one-letter protein string and the per-codon table listing the codon, three-letter code, one-letter code and amino-acid name.
- Click Copy to grab the protein plus the full codon-by-codon breakdown.
Examples
mRNA start to stop
AUGUUUUAA
AUG Met (M), UUU Phe (F), UAA Stop -> protein MF*
DNA coding strand (DNA box on)
ATGGCATAA
T read as U: AUG Met (M), GCA Ala (A), UAA Stop -> protein MA*
Read through a stop (stop-at-first off)
AUGUAAGGG
AUG Met (M), UAA Stop, GGG Gly (G) -> protein M*G
Frequently asked questions
What is a codon?
A codon is a group of three nucleotides that codes for one amino acid. The standard genetic code has 64 codons: 61 specify amino acids and three signal a stop. AUG doubles as the start codon and codes for methionine.
Which genetic code does the tool use?
The standard genetic code, also called NCBI translation table 1. It covers most nuclear genes across life. Alternative tables used by mitochondria and some microbes are not supported, so a few codons there would translate differently.
Can I paste a DNA sequence instead of mRNA?
Yes. Tick 'Input is DNA (read T as U)' and every thymine (T) is converted to uracil (U) before lookup, so a DNA coding (sense) strand translates directly. Paste the coding strand, not the template strand, since the coding strand matches the mRNA.
What happens to leftover bases at the end?
Codons are read in non-overlapping triplets from the very first base. If one or two bases are left over at the end, that partial codon cannot be translated and is ignored. A sequence whose length is not a multiple of three still translates every complete triplet.
Does translation stop at a stop codon?
By default yes. The first stop codon (UAA, UAG or UGA) ends the protein and is shown as Stop in red. Clear 'Stop at first stop codon' to keep reading past it, which is useful for scanning all three internal codons or checking a downstream open reading frame.
Does it pick a reading frame or find the start codon for me?
No. Reading always begins at the first base you paste, so the frame is whatever you give it. To translate frame 2 or 3, delete the first one or two bases before pasting. The tool does not scan for the first AUG on its own.
What if my sequence has invalid characters?
Any character other than A, C, G, U (or T in DNA mode) triggers an error that lists the offending letters. Common culprits are N for an unknown base, gaps, digits from a numbered listing, or a stray T left in mRNA mode. Spaces, tabs and newlines are fine and are removed automatically.
Why does the protein string contain an asterisk?
The asterisk is the one-letter symbol for a stop codon, matching the convention used by NCBI and common bioinformatics tools. So MF* means methionine, phenylalanine, then a stop. The three-letter column shows the same position as Stop.
Is my sequence kept private?
Yes. Translation runs entirely in your browser with no upload, so proprietary or unpublished sequences never leave your device. There is no length cap beyond your device memory.
Learn more
- Reading frames and the genetic code
How the ribosome reads mRNA in triplets, why the reading frame matters, and what the start and stop codons actually do.
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