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.ASN file extension

To open .ASN files on Windows, if the file came from NCBI Pathogen Detection, table2asn, or another NCBI biological workflow, install and open it with NCBI Genome Workbench.

To open a .asn file, first identify where it came from: NCBI Pathogen Detection and many biological ASN.1 files can be opened in NCBI Genome Workbench, while BLAST archive .asn files are typically reformatted with blast_formatter. Do not rename the extension; use the tool that matches the file's source and purpose.

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Last updated: April 29, 2026 · Reviewed by Julian Stricker

Open on your device

Choose your operating system for a dedicated step-by-step opening guide.

How to open .ASN files

Use these platform-specific instructions to open .ASN files safely.

Windows

  1. If the file came from NCBI Pathogen Detection, table2asn, or another NCBI biological workflow, install and open it with NCBI Genome Workbench.
  2. If it is a BLAST archive .asn file, use NCBI BLAST+ blast_formatter to convert it to a readable BLAST report format.
  3. If you only need to inspect the file, try a text editor; if the contents look unreadable, it is likely encoded and needs the appropriate NCBI tool.
Full Windows guide

Mac

  1. Use NCBI Genome Workbench for NCBI ASN.1 biological data such as SNP cluster tree or sequence-related files.
  2. For BLAST archive output, use the NCBI BLAST+ command-line tool blast_formatter to generate a report format you can read.
  3. You may preview a text ASN.1 file in a text editor, but editing it manually can break the schema or make the file unusable.
Full Mac guide

Linux

  1. Open NCBI biological ASN.1 files with NCBI Genome Workbench if it is available for your setup.
  2. For a BLAST archive .asn file, run blast_formatter from the NCBI BLAST+ command-line tools and choose the desired output report format.
  3. Use tools such as file, less, or a text editor only for inspection; they will not necessarily validate or interpret the ASN.1 structure.
Full Linux guide

iOS

  1. iPhone and iPad do not have realistic native support for NCBI .asn workflows; if Files cannot preview it as text, transfer the file to a desktop system and open it with Genome Workbench or BLAST+ tools.
Full iOS guide

Android

  1. Android does not commonly support NCBI .asn files directly; you may view text ASN.1 in a text editor, but for actual use transfer it to a desktop system with Genome Workbench or BLAST+ tools.
Full Android guide

Security notes

  • .asn files are normally data files, not macro-enabled documents, but they should still be opened only with trusted, up-to-date ASN.1-aware software because complex parsers can fail on malformed data.
  • Bioinformatics ASN.1 files may contain sequence data, organism information, sample metadata, or analysis results; treat them as potentially sensitive research or health-related data.
  • Be cautious with very large .asn files from genome or BLAST workflows, as they can consume significant memory or disk space when opened or converted.
  • Do not assume that every file ending in .asn is the same kind of NCBI file; verify the source before uploading it to online tools or sharing it.

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Can't open this file?

These are the most common causes and fixes when .ASN files fail to open.

Common reasons

  • The .asn file opens as unreadable text or symbols
  • Genome Workbench does not open the file correctly
  • The file is a BLAST .asn archive, not a normal report
  • The file does not work after renaming

Fix steps

  1. Confirm the source of the file, such as BLAST, Pathogen Detection, or a GenBank submission workflow.
  2. Use the matching tool: Genome Workbench for supported NCBI biological ASN.1 files, or blast_formatter for BLAST archive output.
  3. Avoid manually editing encoded ASN.1 files in a text editor.

OS-specific troubleshooting

What is a .ASN file?

.asn usually refers to an ASN.1 file, based on Abstract Syntax Notation One, a standardized notation defined by ITU-T X.680. NCBI uses ASN.1 to represent biological information such as sequences, structures, genomes, PubMed records, BLAST archives, and SNP cluster tree data. Some ASN.1 files are human-readable text, while others may appear as encoded or binary-like data and require a compatible parser.

Background

NCBI documents ASN.1 as a format used for biological data including sequences, structures, genomes, PubMed records, and related records. NCBI table2asn can create ASN.1 text files for GenBank submission workflows, often using the .sqn suffix, while BLAST can write archive output as ASN.1 to a .asn file.

Common MIME types: chemical/x-ncbi-asn1-spec

Further reading

Authoritative resources for more details on the .ASN format.

Common .ASN issues

The .asn file opens as unreadable text or symbols

Not every ASN.1 file is plain text. Some are encoded data intended for a specific parser or NCBI tool.

  1. Confirm the source of the file, such as BLAST, Pathogen Detection, or a GenBank submission workflow.
  2. Use the matching tool: Genome Workbench for supported NCBI biological ASN.1 files, or blast_formatter for BLAST archive output.
  3. Avoid manually editing encoded ASN.1 files in a text editor.

Genome Workbench does not open the file correctly

The file may not be the kind of NCBI ASN.1 data that Genome Workbench expects, or it may be incomplete or damaged.

  1. Re-download or re-export the file from the original NCBI tool or data source.
  2. Check whether the file is actually a BLAST archive, which should be handled with blast_formatter instead.
  3. Make sure you are using a current version of the relevant NCBI software.

The file is a BLAST .asn archive, not a normal report

BLAST archive output is saved as ASN.1 and is meant to be reformatted later rather than read directly.

  1. Install the NCBI BLAST+ command-line applications.
  2. Use blast_formatter with the .asn archive as input and select an output format such as a pairwise, tabular, XML, or other supported BLAST report format.
  3. Keep the original .asn archive if you may need to generate different report formats later.

The file does not work after renaming

Changing the extension to or from .asn does not convert the underlying data or encoding.

  1. Restore the original filename if you changed it.
  2. Use an export or conversion feature from the software that created the file.
  3. Ask the sender which program or NCBI workflow produced the file.

FAQ

What program opens .asn files?

For common NCBI biological ASN.1 files, use NCBI Genome Workbench. If the .asn file is a BLAST archive, use the NCBI BLAST+ tool blast_formatter to convert it to a readable report.

Is .asn the same as .sqn?

Not exactly. NCBI table2asn outputs ASN.1 text files that are commonly saved with a .sqn suffix for submission workflows, while .asn is also used for other ASN.1 data such as BLAST archives.

Can I open a .asn file in a text editor?

Sometimes. ASN.1 text files can be inspected in a text editor, but encoded ASN.1 files may look unreadable and should be opened or converted with the proper NCBI tool.

Can I convert .asn by renaming it?

No. Renaming only changes the filename extension. Use Genome Workbench, blast_formatter, or the original generating tool to export or convert the data properly.

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