How a 7z archive is structured
The 7z format is an open, modular archive architecture created by Igor Pavlov for the 7-Zip compression utility.
It begins with a fixed 32-byte StartHeader containing the 6-byte signature 37 7A BC AF 27 1C, version numbers,
and 64-bit relative pointers to the NextHeader block.
The NextHeader structure defines stream mappings, folder codecs, and file metadata. Unlike older archivers that apply compression to individual files independently, 7z defaults to solid compression. In solid mode, multiple similar files are concatenated into a single continuous stream before applying entropy algorithms like LZMA2 or PPMd. This yields massive compression gains for source code repositories and text documents, but requires sequential decoding.
How to extract a 7z file online
- Open your 7z archive. Drop the .7z archive onto the dropzone or click to select from your device. The tool seeks directly to the archive's StartHeader and NextHeader structures for immediate cataloging.
- Review the file inventory. The full file list is populated with real uncompressed sizes, packed byte lengths, compression algorithms (LZMA, LZMA2, PPMd, Copy), and integrity CRC32 values.
- Preview text and scripts. Click View on any configuration file, Markdown doc, JSON export, or text file to inspect it directly in the viewport.
- Save unpacked files or export the manifest. Download stored entries or copy the entire tab-delimited file index to your clipboard for documentation and verification.
What you get out
- Complete file inventory — full paths, directory hierarchies, file names, and byte sizes.
- Compression codec identification — detect whether your archive uses LZMA, LZMA2, BZip2, PPMd, BCJ filter, or AES-256 encryption.
- Archive compression statistics — total file count, folder count, packed stream sizes, unpacked sizes, and calculated compression ratio.
- In-place text previews — view documentation, logs, scripts, and configuration files directly in your browser.
- Exportable audit manifest — download a tab-separated TSV file inventory or copy the manifest to the clipboard.
Which 7z archives this opens
This extractor inspects standard 7z archives created by 7-Zip, PeaZip, WinRAR, p7zip, and modern Linux utilities:
- LZMA and LZMA2 archives — the standard default compression modes for 7-Zip.
- Uncompressed (Copy) containers — archives bundled without compression for rapid staging.
- Single-volume .7z files — standalone archives up to several gigabytes. For multi-part volumes
(
.7z.001,.7z.002), reassemble before opening.
For ZIP archives, use our online ZIP extractor. For WinRAR archives, use our RAR extractor.
Why zero-upload client-side extraction matters
Most online file converter and unzipping sites upload your archive to an external cloud server, run desktop command-line binaries on their backend, and store your uncompressed files on their disks. If your 7z archive holds sensitive source code, database dumps, client databases, or financial records, this represents an unacceptable data leak hazard.
EasyExtract runs 100% locally in your web browser using JavaScript and modern Web APIs. The file is read from your disk into local browser memory. Zero bytes leave your machine, guaranteeing complete privacy and zero data retention.
Format limits and boundary edge cases
Three specific boundary cases are handled with clear notifications:
- AES-256 encrypted headers. If the archive was created with the "Encrypt file names" option enabled, the NextHeader is encrypted with AES-256 and requires entering the master passphrase in offline 7-Zip.
- Solid multi-file stream dependencies. Large solid LZMA2 blocks require decompressing previous files in the stream before extracting later files. Uncompressed files extract immediately.
- Multi-part split volumes. Split archive parts (
.7z.001,.7z.002) must be merged into a single contiguous file before header indexes can be traversed.
When extracting 7z files in the browser helps
- Work computers without administrative rights — open 7z archives on school, library, or corporate computers where installing the 7-Zip desktop application is blocked.
- macOS and iOS devices — Apple operating systems do not include native 7z extraction utilities; open and inspect 7z archives directly in Safari without third-party software.
- Security inspection of unknown archives — inspect file lists, file extensions, and executable payloads before unpacking them to disk.
- Fast audit of archive contents — verify whether a backup archive contains the required file before initiating a lengthy multi-gigabyte restoration.
7z archives compared with ZIP, RAR, and GZ
7-Zip's primary advantage is its unmatched compression ratio. By leveraging LZMA and LZMA2 solid compression, 7z often reduces file sizes by 30% to 70% more than standard ZIP (DEFLATE). However, ZIP remains the universal compatibility standard supported natively by Windows, macOS, and Linux.
For standard archives, use our ZIP extractor. For self-extracting .7z installers, use our in-browser EXE extractor to inspect headers and extract EXE file payloads. For UNIX tarballs, use our TAR and GZ extractor. For detailed architectural benchmarks, read our guide on ZIP vs TAR vs GZ vs 7Z.
7z format standards and solid compression edge cases
The 7z format begins with a 32-byte StartHeader (signature 37 7A BC AF 27 1C,
CRC32, and 64-bit relative offset/size pointers to the NextHeader). The NextHeader holds the stream
mappings, folder definitions, coder configurations (LZMA, LZMA2, PPMd, BCJ), and file tables.
Three extraction edge cases: (a) encoded headers compress the entire file list inside an LZMA/LZMA2 solid block — the extractor inspects the streams and recovers file names and byte offsets; (b) file names are stored as null-terminated UTF-16LE character streams, supporting full international multilingual characters; (c) empty streams indicate either zero-byte files or directory folders — the empty-stream bitmask must be cross-referenced with the empty-file bitmask to distinguish empty files from directories. Read our complete guide on how to extract 7z files online.
Frequently asked questions
How do I open a 7z file without installing 7-Zip?
Drag and drop your .7z archive into the dropzone above. EasyExtract parses the 7z header and catalogs all enclosed files directly in your web browser without installing 7-Zip or any third-party app.
Is my 7z file uploaded to an external server?
No. The archive is read directly from your local disk and processed entirely within your browser's private JavaScript sandbox. Your files and data are never transmitted over the internet.
Can this tool open password-protected 7z archives?
Archives with encrypted headers or encrypted solid blocks are detected and flagged. To decompress AES-256 encrypted 7z streams, use the native desktop 7-Zip utility with your passphrase.
Why is 7z compression better than ZIP?
7-Zip uses modern LZMA and LZMA2 algorithms with dictionary sizes up to 1 GB, combined with solid compression that compresses similar files together. Standard ZIP uses older per-file DEFLATE with 32 KB dictionaries.
Can I open 7z files on a Mac or iPhone?
Yes. macOS and iOS do not include native 7z support. Opening 7z archives with EasyExtract allows you to view and unpack files instantly in Safari or Chrome without installing apps from the App Store.
What is the maximum 7z file size supported?
Because EasyExtract reads the 7z header structures in targeted byte slices, multi-gigabyte archives open smoothly in any modern 64-bit web browser without exhausting memory.
Can I export a list of all files inside a 7z archive?
Yes. Click 'Copy file list' to copy the complete directory inventory to your clipboard, or click 'Download file list' to export a tab-separated (.tsv) audit report.