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+# COS Changelog
+
+An application that generates a changelog between 2 build numbers based on the commit difference between them.
+
+## Usage
+
+Run with `./changelog [global_options] source_build_number target_build_number`
+
+Example: `./changelog --instance cos.googlesource.com --repo cos/manifest-snapshots 15037.0.0 15045.0.0`
+
+## Commands
+`./changelog --help` to see a list of commands or get help for one command
+
+## Global Options
+
+`--instance | -i`: (optional) Specifies the Git on Borg instance where manifest-snapshot files are located. It will use "cos.googlesource.com" by default if not specified.
+
+`--repo | -r`: (optional) Specifies the repository for manifest-snapshot files within the Git on Borg instance. It will use "cos/manifest-snapshots" if not specified.
+
+## Output
+
+Creates 2 JSON files representing the changelog between 2 given build numbers. Each output file maps repositories to their repository changelog. A repository changelog consists of all the commits in a repository that were present in between the build numbers.
+
+All the commits that were present in the target build number and not present in the source build number are located in `source_build_number -> target_build_number.json`.
+
+All commits that were present in the source build number but not present in the target build number are located in `target_build_num -> source_build_num.json`.
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