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Live preview

rules_latex ships two live-preview rules for the "edit-the-source-watch-the-PDF-update" workflow. Both watch the document's transitive sources via LatexInfo and rebuild via bazel build on every save.

latex_serve — system PDF viewer

load("@rules_latex//latex:defs.bzl", "latex_document", "latex_serve")

latex_document(name = "cv", main = "cv.tex", srcs = ["cv.tex"])

latex_serve(
    name = "cv_live",
    document = ":cv",
)

bazel run //:cv_live
# Watching cv.tex
# Built bazel-bin/cv.pdf in 3.2s. Opened in Preview.

The PDF opens once in your system viewer (Preview on macOS, xdg-open on Linux, start on Windows). Subsequent rebuilds rely on the viewer's own auto-reload behaviour:

Viewer Auto-reload?
macOS Preview
Linux Evince
Linux Okular
Adobe Reader (locks the file)
Chrome PDF viewer (manual refresh)

latex_serve_web — in-browser preview

For an Overleaf-style experience, declare a latex_serve_web target:

load("@rules_latex//latex:defs.bzl", "latex_document", "latex_serve_web")

latex_document(
    name = "cv",
    main = "cv.tex",
    srcs = ["cv.tex"],
    synctex = True,   # enables click-to-source
)

latex_serve_web(
    name = "cv_web",
    document = ":cv",
)

bazel run //:cv_web
# serving live preview at http://127.0.0.1:8765/

Open the URL in your browser. The page:

  • Renders the PDF with PDF.js (vendored, no CDN dependency).
  • Listens for "reload" events over Server-Sent Events.
  • Preserves scroll position across reloads.
  • When synctex = True is set on the document, clicking anywhere in the rendered PDF resolves to a source file:line displayed in the footer bar.

How fast is the loop?

For a small document (single-page CV, hello-world) paired with a cache snapshot, steady-state rebuilds complete in 200–400 ms. First build is slower (the online prime takes ~30 s) but happens exactly once per content-hash of the inputs — Bazel's action cache handles the rest.

For larger documents (multi-chapter thesis, paper with figures), the TeX compile itself dominates and rebuilds run in 2–5 s.

What gets watched?

The watcher monitors every .tex, .bib, image, and other file in the document's srcs plus transitively via deps. Edits to the toolchain binary or the cache snapshot are picked up by Bazel's analysis layer, so they trigger correct rebuilds too.

External-repo files (e.g. from a latex_library published in another Bazel module) are not watched. Edit those and re-run bazel run //:cv_web to pick up the change.

Architecture

Both rules synthesise a small launcher script that:

  1. Polls the watched paths every 250 ms via os.stat.
  2. Shells out to bazel build <document_label> on change.
  3. latex_serve opens the PDF once; latex_serve_web keeps a tiny HTTP server alive and pushes SSE events to connected browser tabs.

Both use the same bazel build invocation as a normal build, which means live-mode behaviour is identical to CI — no "works locally, fails in CI" drift. See DESIGN.md §4.7 for the rationale.