TXT to FASTA Converter

Turn plain text or CSV sequences into a FASTA file. Choose how records are separated, check the sequence alphabet, then download your result.

Conversion runs in your browser. Sequence contents and file names are not sent by this tool.

1. Add sequences

UTF-8 text only. Maximum 5 MiB, 10,000 sequences and 256 CSV columns.

Input format
Examples

2. Choose output settings

Sequence alphabet

Sequence line length

Gaps and stop symbols are rejected unless enabled. Check whether your downstream program accepts them.

Letters become uppercase. Spaces, tabs and sequence line breaks are removed. Other invalid characters stop conversion. T and U are never exchanged.

3. Review FASTA

Your FASTA preview will appear after conversion.

How to convert TXT or CSV to FASTA

  1. 1

    Set the record boundaries

    Choose one sequence for wrapped TXT, or one sequence per nonempty line for a list. Blank lines in TXT are ignored. CSV uses one record per data row and requires a header row.

  2. 2

    Choose the alphabet and identifiers

    Select DNA, RNA or protein explicitly. TXT gets the ID or numbered prefix you provide. CSV preserves the selected ID column exactly and rejects duplicate IDs or whitespace in identifiers.

  3. 3

    Validate and download

    Each FASTA record begins with > and its ID, followed by the sequence. Review the sequence count and preview, then download the complete .fasta file.

A two-record CSV example

Map sample_id to the ID column and sequence to the sequence column. DNA mode produces two records with 12 sequence symbols in total.

samples.csv
sample_id,sequence
sample_1,ACGTNN
sample_2,GGTTAC
samples.fasta
>sample_1
ACGTNN
>sample_2
GGTTAC

Related sequence tools

Format references

Questions about FASTA conversion

Which sequence letters are accepted?

DNA accepts A, C, G, T and the IUPAC ambiguity codes R, Y, S, W, K, M, B, D, H, V and N. RNA uses U instead of T. Protein accepts the 20 standard amino acids plus B, X, Z, J, U and O. Lowercase letters become uppercase.

Can I upload an Excel workbook or an existing FASTA file?

Save an Excel sheet as UTF-8 CSV first. This tool accepts raw TXT sequences or comma-separated CSV, not XLSX, FASTQ or existing FASTA records. A FASTA header pasted as sequence text is rejected so records cannot be silently joined.

Does the converter clean invalid characters or translate sequences?

It removes spaces, tabs and sequence line breaks and uppercases letters. It does not delete invalid symbols, replace T with U, translate DNA into protein, align sequences or remove gaps. Gap and protein stop symbols require explicit permission.

Will this file work for a GenBank submission?

The output uses the basic FASTA structure. Submission systems can require shorter IDs, organism information and restrictions on gap symbols. This converter does not add those annotations or certify a submission. Check the requirements of your destination.

What happens to other CSV columns?

Only the selected ID and sequence columns are exported. Other columns, including annotations and descriptions, are left out. CSV data rows with missing fields, empty sequences or repeated IDs stop the conversion.