AMindToThink/latex-semantic-linebreaks

LaTeX semantic linebreaks (one-sentence-per-line)

LaTeX collapses single newlines in source to spaces in the rendered PDF, so reformatting prose to one-sentence-per-line is a pure-source change with zero rendering impact. The convention is variously called "semantic linebreaks", "ventilated text", or "one sentence per line".

When to apply this skill

Apply when:

• A LaTeX paper source has multi-sentence paragraphs written as long single lines (which makes Edit() brittle and git diff paint whole paragraphs red).
• You're about to make many small prose edits across a paper.
• A user asks to "format" a paper, reflow .tex prose, or set up "sentence-per-line".

Do NOT apply mid-paragraph during a single small edit — it inflates that edit's diff. Run as a dedicated formatting commit, separate from semantic changes.

Why an off-the-shelf tool will not work

Three off-the-shelf tools were evaluated and rejected. Do not retry them.

| Tool | Verdict | |---|---| | latexindent --m oneSentencePerLine (TeX Live) | Produces ~14 false breaks per math-heavy paper. Categories: tikz/factorial ! mistaken for sentence end (orange!70!black, 1/n!); quote-attached ?'' split off; \texttt{.} content broken; escaped-space vs.\ broken; abbrev etc.) split before comma; footnote .1 ambiguous. Tuning knobs (betterFullStop, sentencesBeginWith, sentencesDoNotContain) shift which categories fire but never eliminate them. Matches multiple closed-but-not-fully-fixed bugs in the latexindent.pl tracker. | | tex-fmt (Rust) | Semantic-linebreaks support is an open feature request (issue #80) as of early 2025. Not implemented. | | andykuszyk/texfmt (Go) | Archived September 2024. Only does fixed-width reflow, not sentence-per-line. |

If you find yourself trying to install latexindent or tune its config, stop. Use the project-local Python script described below.

Tool: state-aware Python formatter

A reference implementation lives in references/format_sentences.py of this skill. It is ~150 LoC and:

• Tracks math mode ($...$, $$...$$, \(...\), \[...\]).
• Skips environments where breaks are wrong: verbatim, lstlisting, tikzpicture, equation, equation*, align, align*, gather, gather*, eqnarray, eqnarray*, multline, multline*, array, matrix, pmatrix, bmatrix, vmatrix, cases, pgfplots, axis, tabular, tabular*, tabularx.
• Skips opaque command arguments: \texttt, \textcolor, \cite, \citep, \citet, \citeyear, \ref, \label, \url, \href, \verb.
• Skips %-comments (with \% escaped form preserved).
• Recognizes abbreviations: e.g., i.e., i.i.d., cf., vs., et al., etc., Fig., Eq., Sec., Tab., Ref., Refs., Eqs., Figs., Tabs., Secs., App., Apps., Alg., No.. Add to ABBREVS if your paper uses others.
• Handles escaped backslashes \\ before any single-char inspection, so \\[1em] (LaTeX linebreak + optional spacing) is not mistaken for \[ display math opener. This was a real bug; see the regression test below.
• Inserts \n only after [.?!], optionally past attached '' or ", then whitespace, then capital letter — provided no abbreviation matches the preceding ~12 chars.
• Idempotent: re-running on already-formatted source inserts nothing.

The companion test file references/test_format_sentences.py has 24 cases covering every edge case the script handles, including the runaway-skip-region regression. Run the tests before trusting the script in a new project.

Workflow

# 1. Stage the script in the project (one-time setup).
mkdir -p scripts tests
cp ~/.claude/skills/latex-semantic-linebreaks/references/format_sentences.py \
   scripts/format_paper_sentences.py
cp ~/.claude/skills/latex-semantic-linebreaks/references/test_format_sentences.py \
   tests/test_format_paper_sentences.py
uv run pytest tests/test_format_paper_sentences.py -v   # expect 24 green

# 2. Commit any pending semantic .tex changes FIRST — keep formatting
#    in its own commit so reviewers can tell prose changes from reflow.
git add paper/your_paper.tex && git commit -m "..."

# 3. Run the formatter to a sibling file and review the diff.
python scripts/format_paper_sentences.py \
  paper/your_paper.tex /tmp/formatted.tex
diff paper/your_paper.tex /tmp/formatted.tex | less   # newlines only, no word changes

# 4. Apply, rebuild, and verify byte-identical rendered text.
cp /tmp/formatted.tex paper/your_paper.tex
cd paper && rm -f your_paper.{aux,bbl,blg,fdb_latexmk,fls,log,out} && \
  latexmk -pdf your_paper.tex

# 5. Verification — both byte counts MUST match exactly.
pdftotext -nopgbrk paper/your_paper.pdf -      | tr -s ' \n\t' ' ' | wc -c
# Compare against pre-format byte count (record this BEFORE step 4).

# 6. Commit format change separately.
git commit -am "format: sentence-per-line reflow (no semantic changes)"

Verification rules

Two checks, both required.

Rule 1: byte-identical rendered PDF text

pdftotext -nopgbrk before.pdf - | tr -s ' \n\t' ' ' | wc -c
pdftotext -nopgbrk after.pdf  - | tr -s ' \n\t' ' ' | wc -c

These two byte counts must match exactly. A pdftotext -layout line-by-line diff is misleading — column-position differences in extracted text produce tens of false-positive diff lines for purely cosmetic source reflow. The whitespace-collapsed -nopgbrk byte-count comparison is the right test.

Rule 2: visually inspect the .tex

Byte-identical rendering does not guarantee the source got reflowed where you intended. A formatter bug (e.g., a runaway skip region from misparsing \\[) can leave whole paragraphs unformatted while still producing identical PDF output. After running, visually scan a few paragraphs in the .tex — every prose paragraph should have one sentence per line. If any paragraph is still a single long line, the skip-region detection is broken; debug it.

This is not theoretical: the original implementation of this script left ~25 lines unformatted (the abstract and §Motivation opening), and only Rule 1 verification missed it. The user's visual check caught it.

Anti-patterns

• Don't reformat in the same commit as semantic changes. Reviewers can't tell a sentence reorder from a sentence move.
• Don't reformat when the abstract has math at the wrong place. If \\[1em] or similar shows up in \title, \author, or \date, ensure the formatter handles \\ escapes — the reference script does.
• Don't trust pdftotext-layout diffs. They will spook you with hundreds of "differences" that are just column-position changes.
• Don't recommend latexindent. See above. It will not converge.

Quick decision rule

Is the .tex source one-sentence-per-line in the paragraph you're editing?
├── Yes  → just edit; don't reformat.
└── No   → if you're making >2 prose edits, run the workflow above
          first as a separate commit. If you're making one quick edit,
          either skip reformatting (acceptable) or reformat just the
          paragraph by hand inside the Edit() call.