reviewdog is a Go CLI that bridges linter output to code review platforms. It consumes diagnostic output from any linter or compiler via stdin in multiple formats — Vim errorformat, SARIF 2.1.0, Checkstyle XML, the project's own RDJSON/RDJSONL protobuf-defined format, or raw unified diff — parses it, filters findings against a code diff so only issues on changed lines get posted, and reports them to GitHub (check runs, PR reviews, annotations), GitLab MRs, Bitbucket, Gerrit, or Gitea, or writes them locally in text, RDJSON, or SARIF form. The core architecture is a set of loosely coupled Go packages: parser/ for format decoders, diff/ for unified diff parsing, filter/ for diff-aware result filtering, service/ for per-platform comment and diff API clients, cienv/ for CI context detection, and project/ for executing multi-runner .reviewdog.yml configs. The CLI entry point is cmd/reviewdog/main.go, with orchestration in reviewdog.go around the CommentService and DiffService interfaces; command flow is: subprocess or stdin -> parser -> ResultMap -> diff filter -> reporter service -> host-platform API.