FASTA GC Content & Reverse Complement

Paste DNA/RNA or multiple FASTA records and choose Analyze. The overview shows length including IUPAC symbols, GC content and ambiguous-base count. For multiple records, select the sequence used for output and base counts.

GC % = 100 × (G+C)/(A+C+G+T+U). Ambiguous IUPAC symbols are excluded from this denominator but never deleted. With no unambiguous bases the value is —. Base counts includes the minimum and maximum possible GC percentage over the entire sequence: S is certainly GC, W certainly AT, and other codes can have mixed possibilities.

The reverse complement is output in the 5′→3′ direction and preserves all IUPAC codes, e.g. R↔Y and B↔V. As input uses U for RNA records and T otherwise; records without T/U default to DNA. Output choice changes only the alphabet, not the original input statistics.

Copy takes the selected sequence without a header. FASTA exports all reverse complements with original headers plus RC, or sequence_1 for raw input. Sequence lines have at most 80 characters. CSV contains statistics for every record and code; percentages use twelve significant digits.

Whitespace and lowercase are accepted. Headers start with > and need a name. Numbers, gaps, other symbols, empty records, raw sequence before a FASTA header and mixed T/U within a record are rejected. At most 500,000 bases in total, 200 records and one million input characters; nothing is truncated. Processing is local.