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+[**attrsum**](https://git.eeqj.de/sneak/attrsum/) is a **Go
+1.22** command-line utility that **adds, updates, verifies, and clears per-file
+file content checksums stored in extended attributes (xattrs) on macOS (APFS) and
+Linux**, released under the [WTFPL v2](http://www.wtfpl.net/).
+
+Original release 2025-05-08.
+
+Current version 1.0 (2025-05-08).
+
+---
+
+## Getting Started — Quick Build
+
+```bash
+# prerequisites: Go 1.22+
+git clone https://git.eeqj.de/sneak/attrsum.git
+cd attrsum
+go build -o attrsum .
+```
+
+### Install
+
+```bash
+go install git.eeqj.de/sneak/attrsum@latest   # into GOPATH/bin or $(go env GOBIN)
+```
+
+Semantic Versioning 2.0.0 is used for tags.
+
+---
+
+## Usage
+
+```bash
+# add checksum & timestamp xattrs to every regular file under DIR
+attrsum sum add DIR
+
+# update checksum only when file mtime is newer than stored sumtime
+attrsum sum update DIR
+
+# verify checksums, stop on first error
+attrsum check DIR
+
+# verify every file, reporting each result, keep going after errors
+attrsum -v check --continue DIR
+
+# remove checksum & timestamp xattrs
+attrsum clear DIR
+```
+
+| xattr key                                   | meaning                        |
+|---------------------------------------------|--------------------------------|
+| `berlin.sneak.app.attrsum.checksum`         | base-58 multihash (sha2-256)   |
+| `berlin.sneak.app.attrsum.sumtime`          | RFC 3339 timestamp of checksum |
+
+Flags:
+
+* `-v, --verbose` — per-file log output
+* `--exclude PATTERN` — skip paths matching rsync/Doublestar glob
+* `--exclude-dotfiles` — skip any path component that starts with `.`
+
+`attrsum` **never follows symlinks** and skips non-regular files (sockets, devices, …).
+
+---
+
+## Why?
+
+Apple APFS and Linux ext3/ext4 **store no per-file metadata checksums**, so
+silent data corruption can pass unnoticed.  `attrsum` keeps a portable,
+tamper-evident checksum **inside each file’s xattrs**, providing integrity
+verification that travels with the file itself—no external database
+required.  Now you can trust a USB stick didn't eat your data.
+
+---
+
+## Contributing
+
+* Author & maintainer: **sneak** – <sneak@sneak.berlin>
+* Issues / PRs: <https://git.eeqj.de/sneak/attrsum/>
+* Code must pass `go vet`, `go test ./...`, and `go fmt`.
+* No CLA; contributions are under WTFPL v2.
+
+---
+
+## Community & Support
+
+Bug tracker and wiki are in the Gitea repo linked above.
+
+No formal Code of Conduct; be excellent to each other.
+
+---
+
+## License
+
+*Everything is permitted.*
+See [WTFPL v2](http://www.wtfpl.net/txt/copying/).