How is a reverse complement calculated?

The tool complements each symbol using the selected alphabet and then reverses the sequence. DNA pairs A with T and C with G; RNA pairs A with U and C with G. Reverse alone changes order without complementing, while complement alone keeps the original order. For DNA AAGC, complement gives TTCG, reverse gives CGAA, and reverse complement gives GCTT.

Are IUPAC ambiguity symbols supported?

Yes. R pairs with Y, K with M, B with V, and D with H. S, W and N complement to themselves. Case is preserved unless you explicitly choose uppercase or lowercase output.

What happens to FASTA headers and empty records?

Headers beginning with > at the start of a line are preserved as entered and are never interpreted as sequence. Records keep their order and transform independently. An empty record remains present and is labelled empty in the record summary.

Can I reverse-complement multiple sequences as a batch?

Yes. Paste multiple FASTA records in the Sequence or FASTA box. Each record gets its own transformation and counts; headers and record order remain unchanged. Plain text without FASTA headers is treated as one sequence, even across multiple lines.

DNA mode accepts T and RNA mode accepts U. The other symbol is rejected unless you explicitly enable U-to-T or T-to-U conversion. The result reports how many such conversions occurred.

What do invalid-character positions mean?

Sequence positions count non-whitespace characters within a record, starting at one. Line and column identify the character in the original input. The tool lists the first 200 invalid positions and gives the total; correct those and recheck.

How do TXT and FASTA exports differ?

TXT contains the transformed text, retaining headers when your input was FASTA. FASTA export adds a generated sequence header to plain input and preserves existing headers for FASTA input. Both follow the selected line width.

Does this analyze biological activity?

No. It is a symbolic text transformation, not a biological interpretation, diagnostic tool or primer assessment. Counts describe output symbols only. Inputs stay in this browser and are not saved; the input limit is 1 MiB.

Can I reverse-complement primer or oligo text?

Yes. Enter the sequence and use the DNA alphabet for a symbolic reverse complement, including supplied text used in a polymerase chain reaction (PCR) workflow. Reverse complement writes the complementary strand in the opposite order; reversing alone does not change the bases. This does not design primers, choose a binding site, or assess PCR performance.

Why is a reverse primer written as a reverse complement?

The two strands of DNA run antiparallel: one runs 5′ to 3′ while its complementary strand runs 3′ to 5′. Sequence text is conventionally written 5′ to 3′, so the complementary strand must be reversed to write it in that same orientation. For a supplied DNA sequence 5′-AAGC-3′, the paired strand is 3′-TTCG-5′ and its 5′-to-3′ text is GCTT. This explains the orientation of reverse-primer sequence text; the tool does not choose a binding site, design a primer or assess PCR performance.

Can I use this as a reverse-complement program or software?

Yes. This is free browser software for reversing, complementing or reverse-complementing supplied DNA or RNA text. Paste plain sequence text or FASTA records, choose the alphabet and operation, then copy or save the result. It runs on this page; no native installation is required.

Sequence Reverse Complement

Paste a plain sequence or multiple FASTA records, select DNA or RNA, and choose reverse, complement or reverse complement. Each FASTA record transforms independently while its header and order remain intact. Choose output case and line width, inspect per-record counts, and copy or download the result. Invalid symbols stop output and identify their record, sequence position, line and column.

AlphabetTransformationLetter caseLine width

Explicitly convert U to T before transformationSequence or FASTA

Up to 1 MiB. Whitespace inside sequences is ignored. FASTA headers must start with > at the beginning of a line and are preserved exactly.

Enter a sequence or FASTA records.

Symbolic sequence transformation only; no biological activity, diagnosis, primer suitability or synthesis guidance. Processing is local; input and output are not saved between visits. Counts describe the output sequence.

Common questions

How is a reverse complement calculated?: The tool complements each symbol using the selected alphabet and then reverses the sequence. DNA pairs A with T and C with G; RNA pairs A with U and C with G. Reverse alone changes order without complementing, while complement alone keeps the original order. For DNA AAGC, complement gives TTCG, reverse gives CGAA, and reverse complement gives GCTT.
Are IUPAC ambiguity symbols supported?: Yes. R pairs with Y, K with M, B with V, and D with H. S, W and N complement to themselves. Case is preserved unless you explicitly choose uppercase or lowercase output.
What happens to FASTA headers and empty records?: Headers beginning with > at the start of a line are preserved as entered and are never interpreted as sequence. Records keep their order and transform independently. An empty record remains present and is labelled empty in the record summary.
Can I reverse-complement multiple sequences as a batch?: Yes. Paste multiple FASTA records in the Sequence or FASTA box. Each record gets its own transformation and counts; headers and record order remain unchanged. Plain text without FASTA headers is treated as one sequence, even across multiple lines.
Can I mix T and U?: DNA mode accepts T and RNA mode accepts U. The other symbol is rejected unless you explicitly enable U-to-T or T-to-U conversion. The result reports how many such conversions occurred.
What do invalid-character positions mean?: Sequence positions count non-whitespace characters within a record, starting at one. Line and column identify the character in the original input. The tool lists the first 200 invalid positions and gives the total; correct those and recheck.
How do TXT and FASTA exports differ?: TXT contains the transformed text, retaining headers when your input was FASTA. FASTA export adds a generated sequence header to plain input and preserves existing headers for FASTA input. Both follow the selected line width.
Does this analyze biological activity?: No. It is a symbolic text transformation, not a biological interpretation, diagnostic tool or primer assessment. Counts describe output symbols only. Inputs stay in this browser and are not saved; the input limit is 1 MiB.
Can I reverse-complement primer or oligo text?: Yes. Enter the sequence and use the DNA alphabet for a symbolic reverse complement, including supplied text used in a polymerase chain reaction (PCR) workflow. Reverse complement writes the complementary strand in the opposite order; reversing alone does not change the bases. This does not design primers, choose a binding site, or assess PCR performance.
Why is a reverse primer written as a reverse complement?: The two strands of DNA run antiparallel: one runs 5′ to 3′ while its complementary strand runs 3′ to 5′. Sequence text is conventionally written 5′ to 3′, so the complementary strand must be reversed to write it in that same orientation. For a supplied DNA sequence 5′-AAGC-3′, the paired strand is 3′-TTCG-5′ and its 5′-to-3′ text is GCTT. This explains the orientation of reverse-primer sequence text; the tool does not choose a binding site, design a primer or assess PCR performance.
Can I use this as a reverse-complement program or software?: Yes. This is free browser software for reversing, complementing or reverse-complementing supplied DNA or RNA text. Paste plain sequence text or FASTA records, choose the alphabet and operation, then copy or save the result. It runs on this page; no native installation is required.

Symbolic sequence transformation only; no biological activity, diagnosis, primer suitability or synthesis guidance.