Generate the reverse, complement and reverse-complement of any DNA or RNA sequence instantly. Paste your sequence below — the tool detects RNA automatically, supports IUPAC ambiguity codes, and lets you copy each result with one click.
Accepts A, C, G, T, U and IUPAC ambiguity codes (R, Y, S, W, K, M, B, D, H, V, N). Other characters are ignored. RNA is detected automatically (U without T).
How to use this reverse-complement tool
- Paste your sequence (5’→3′) into the box. Case, spaces and line breaks don’t matter.
- Read the three outputs. Reverse (sequence read backwards), complement (each base paired), and reverse-complement (the opposite strand, 5’→3′).
- Copy any result with its Copy button. The tool also reports length, GC% and whether it read your input as DNA or RNA.
What is the reverse complement?
DNA is double-stranded and antiparallel: the two strands run in opposite directions and pair A–T and G–C (A–U in RNA). The reverse complement of a sequence is the sequence of the opposite strand, written in the conventional 5’→3′ direction. It is one of the most common operations in molecular biology, and it is easy to confuse three related transformations:
- Reverse — the same bases read from 3′ to 5′ (no base changes). Rarely used on its own.
- Complement — each base swapped for its pair (A↔T, G↔C), keeping the 5’→3′ order. This is not the opposite strand.
- Reverse complement — complement and reverse. This is the actual sequence of the opposite strand and the one you almost always want.
Worked example
For the top strand 5'-ATGCTAGC-3':
- Reverse:
CGATCGTA - Complement:
TACGATCG - Reverse complement:
GCTAGCAT← the opposite strand, 5’→3′
When do you need it?
- Primer design. A reverse primer is the reverse complement of the 3′ end of the target region. Designing it by hand is the classic place to make a mistake.
- Cloning. Checking the orientation of inserts, annealing oligos, and reading restriction sites on the opposite strand.
- Sequencing. Aligning reads from the reverse strand, or converting a reverse read into the sense strand.
- siRNA / oligo design and any time you need the antisense strand.
DNA, RNA and IUPAC codes
If your sequence contains U (and no T) the tool treats it as RNA and complements with A–U pairing. It also understands the full set of IUPAC ambiguity codes (R, Y, S, W, K, M, B, D, H, V, N), complementing them correctly — for example R (A/G) becomes Y (C/T). Characters outside the nucleotide alphabet are ignored, so you can paste FASTA lines or messy text without cleaning them first.
Frequently asked questions
What is the difference between complement and reverse complement?
The complement swaps each base for its pair but keeps the 5’→3′ order, so it is not a real strand. The reverse complement also reverses the order, giving the actual opposite strand read 5’→3′. For primer design you want the reverse complement.
Does the tool work for RNA?
Yes. If the sequence contains U and no T it is treated as RNA, and complements use A–U pairing so the outputs contain U instead of T.
Does it support ambiguity (degenerate) codes?
Yes. All IUPAC codes (R, Y, S, W, K, M, B, D, H, V, N) are complemented correctly, which is useful for degenerate primers.
Is my sequence sent to a server?
No. The calculation runs entirely in your browser; nothing is uploaded.
How do I get a reverse primer from my template?
Take the region at the 3′ end of your target on the sense strand and compute its reverse complement — that sequence is your reverse primer (5’→3′).
Related guide: How to design PCR primers →
