What is the AB1 file format?
An .ab1 file is a binary chromatogram produced by Applied Biosystems (now Thermo Fisher Scientific) capillary DNA sequencers, storing the raw and processed output of a single Sanger sequencing run. The format is officially called ABIF - Applied Biosystems Genetic Analysis Data File Format.
The file opens with a four-byte ASCII magic string ABIF, followed by a version field and a 128-byte header that records the offset of the tag directory. The body uses a TIFF-inspired tagged structure: each directory entry specifies a four-character tag name, data type code, element count, data size, and either an inline value (for entries ≤ 4 bytes) or an offset pointing to a data block elsewhere in the file. Core data blocks include raw fluorescence intensities for four dye channels (DATA tags 1-4 and 105-108), processed base calls (PBAS 2), Phred-equivalent quality scores (PCON 2), and peak position indices (PLOC 2). Instrument metadata - model, run name, injection parameters - are stored in additional named tags.
One .ab1 file represents a single capillary read, typically covering 600-1,000 base pairs. For high-throughput next-generation sequencing, the dominant format is FASTQ, but Sanger sequencing continues to produce .ab1 as its primary output. It remains the standard for verifying short targeted sequences such as plasmid inserts and PCR products.
The older extension .abi refers to the same ABIF format and is produced by some older Applied Biosystems instruments.
Security & safety
RISK: LOWBinary scientific data file; no executable code. Safe to open in any viewer. Files received from sequencing services contain only DNA sequence data.
Format details
in a nutshellPrograms that open AB1 files
Windows7 apps
SnapGene
Paid Full-featured cloning software; open .ab1 via File → Import Sequencing Data for alignment against reference. 
BioEdit
Free Legacy sequence editor; can open .ab1 chromatograms. Last updated 2013 - functional but unmaintained. 
ChromasPro
Paid Advanced trace viewer with assembly; open .ab1, batch trim by quality, assemble reads.
Chromas Lite
Free Open .ab1 file directly; view trace, edit base calls, export sequence as text/FASTA.
SnapGene Viewer
Free File → Open → select .ab1 file; displays chromatogram trace with quality values, allows export to FASTA/GenBank. 
macOS3 apps
Linux2 apps
Science Codons AB1 Viewer
Free Upload .ab1 in browser; view trace and export sequence online - no install needed. Technical details
deep spec| Magic bytes | ASCII ABIF (0x41 0x42 0x49 0x46) at offset 0 |
| Encoding | Binary |
| Byte order | Big-endian |
| Header | 128 bytes: magic ABIF, file type byte, version (0x0065 = v1.01), tag directory offset and entry count |
| Tag structure | TIFF-inspired directory: 4-char tag name, tag number, data type code, element count, element size, data size, inline value or file offset |
| Core data tags | Raw fluorescence for 4 dye channels (DATA 1-4, 105-108), base calls (PBAS 2), quality scores (PCON 2), peak positions (PLOC 2) |
| Typical size | 50 KB - 500 KB per single capillary read |
| Sequence coverage | One file per capillary read, typically 600-1,000 base pairs |
| Instrument series | Produced by ABI PRISM 377, 3100, 3130, and 3730 capillary DNA sequencer series |
| Specification version | ABIF v1.01 (July 2006 spec); format stable since mid-1990s introduction |
| Developer lineage | Applied Biosystems → Life Technologies (2008) → Thermo Fisher Scientific (2014) |
| MIME type | application/octet-stream (chemical/seq-na-abif also used in bioinformatics contexts) |
| Alternative extension | .abi - same ABIF format, produced by some older Applied Biosystems instruments |
| Released | 1994 (ABI PRISM 377 sequencer) |
| Latest version | ABIF v1.01 (specification July 2006; format stable since mid-1990s) |
| Specification | cdn.thermofisher.com |
AB1 conversions
Community Q&A
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