ToolerWork
Biology

Codon Lookup Tool

Look up a DNA or RNA codon to find its amino acid, abbreviation and stop-codon status.

Your codon

One triplet, written 5′ → 3′

Accepts A/C/G/T or A/C/G/U. No ambiguous bases or mixed T/U.

Sequences are processed locally and are not uploaded or saved by this tool.

Your result, clearly explained

Paste a sequence or load the example, then run the tool. Your sequence stays in this browser.

How to use

  1. Enter one triplet

    Type three DNA or RNA bases, such as ATG or AUG.

  2. Read the assignment

    See the amino acid, one-letter code and three-letter abbreviation.

  3. Explore synonyms

    Review the other standard-code codons for the same amino acid.

Why ToolerWork?

Private by design

Sequence calculations run inside your browser.

Clear assumptions

Strand direction, code table and approximation limits are explained.

Related Tools

View All
Codon Table Explorer

Explore all 64 standard-code codons. Search amino acids and switch between DNA and RNA notation.

DNA to Protein Translator

Translate DNA into amino acids in any of six reading frames using the standard genetic code.

ORF Finder

Find ATG-start open reading frames on both DNA strands, with coordinates and translated proteins.

Why use this tool?

  • Accept DNA and RNA notation with the same standard-code assignment.
  • Distinguish amino acids from termination signals.
  • See synonymous codons without searching a full chart.

Method & assumptions

Codons are read 5′→3′ using NCBI table 1. RNA U is mapped to DNA T for lookup. Mixed T/U input and ambiguous letters are rejected. ATG/AUG is highlighted as the canonical start; initiation can depend on biological context.

References: NCBI genetic codes

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Frequently asked questions

Can I enter AUG instead of ATG?

Yes. AUG and ATG both map to methionine in RNA and DNA notation, respectively. Do not mix T and U in the same triplet.

Which codons mean stop?

TAA, TAG and TGA in DNA notation, or UAA, UAG and UGA in RNA notation, are the three standard-code stops.

Why do several codons give the same amino acid?

The genetic code is degenerate: more than one triplet can encode an amino acid. The result lists these synonymous codons.

Are mitochondrial codes supported?

No. This lookup uses the standard genetic code only. Some mitochondrial and organism-specific codes assign certain codons differently.

Is every ATG the beginning of a gene?

No. ATG encodes methionine and can be an internal codon. Initiation depends on surrounding signals and the organism.