DNA / RNA Reverse Complement Online Converter
Primer design, cloning, and sequencing orientation checks all require computing the reverse complement on a near-daily basis.
The logic is straightforward and takes two steps: first, replace each base according to pairing rules (A↔T, G↔C; A↔U in RNA), then flip the entire sequence end-to-end. The flip is necessary because the two DNA strands run antiparallel: if one strand is written 5’→3’, its complement runs 3’→5’ in the physical duplex, and convention is to write all sequences 5’→3’.
The tool also handles IUPAC degenerate bases (R=A/G, Y=C/T, N=any, etc.) by applying the symmetric complement mapping over the degenerate set,
so it works directly for degenerate primer design. Input can be a bare sequence or a full FASTA block (lines starting with > are ignored).
All computation runs in your browser; the sequence never leaves your machine.
FAQ
What is the difference between reverse complement and complement?
Complementing alone swaps each base by pairing rules (A→T, G→C) without changing the strand orientation. Reverse complement does that and then flips the sequence end-to-end, giving you the complementary strand written 5'→3' as convention requires. Reverse primers are always designed as the reverse complement.
Are degenerate bases supported?
Yes. R/Y/S/W/K/M/B/D/H/V/N are all handled with symmetric IUPAC complementation — for example, R (A/G) complements to Y (C/T).
Is the sequence uploaded to a server?
No. All computation runs locally in your browser; the page contains no upload logic.
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