Sembr

Sembr

The sembr slice puts each sentence of a Markdown file on its own line. This is called semantic line breaks. Diffs get smaller and files are easier to read. The slice also puts each Markdown heading in Title Case.

What It Does for You

The slice has one tool.call hook with the phase rewrite. It runs for the tools Write, Edit, and Bash. It changes the input of the call before Claude Code runs the call. It runs before the phase check of the guard slice, so the guards see the changed call.

Tool	What the hook rewrites
Write	The content of a .md or .mdx file
Edit	The new_string of an edit to a .md or .mdx file, and a repair of old_string
Bash	The quoted heredoc of git commit -m and gh pr create --body

A file of another type keeps its content. The slice has no userConfig key and no hook command.

How the Hook Finds a Sentence End

The hook uses Intl.Segmenter with sentence granularity and the locale und. These are the Unicode sentence rules (UAX 29), and they give the same result on each host. The hook has no list of abbreviations. So a break can follow e.g. when the segmenter sees a sentence end there. Markdown still shows the same paragraph.

The hook only adds breaks after a sentence end. It never joins lines. It never breaks a line at a column or in a word. A second run on the same text gives the same text.

What the Hook Keeps

The hook does not change:

• A front matter block, a fenced code block, an indented code block, and a table.
• A <pre> block, a <code> block, and a $$ math block.
• Inline code, a link, a reference link, an HTML tag, and a URL. A break never falls inside one of them.
• A line that ends with two spaces or a backslash, because it is a hard break.
• A reference definition, a rule line, a line that starts with < or |, and a line before a setext underline.
• A line that looks like code, such as a line with {, }, or =.

A list item and a quote keep their prefix on each new line. A file with CRLF line endings keeps CRLF on each line that the hook writes.

Edits That Cross a Sentence Break

Claude Code checks old_string before a classic hook runs, so only a hooks module can repair it. When old_string is not in the file, the hook splits it into sentences. If the split text is in the file, the hook uses it as old_string and splits new_string the same way. If a list item or a quote holds the match, the hook takes the line prefix from the file. The hook repairs an edit only when exactly one place matches.

The hook rewrites new_string only when the edit starts and ends at line bounds of the file. It leaves an edit alone when it has replace_all, an empty new_string, or a file that the hook cannot read. The split runs on the whole file after the edit, so a fence or a table around the lines stays intact.

Commit and Pull Request Text

The hook rewrites a heredoc in a Bash command in two forms only:

• git commit -m "$(cat <<'EOF' ... EOF)"
• gh pr create --body "$(cat <<'EOF' ... EOF)"

The command stays as written when:

• An output line would equal the delimiter, because the heredoc would end early.
• The command has more than one heredoc.

Two parts of a commit message stay as written:

• The subject line.
• The last paragraph, when each of its lines is a trailer, such as Co-Authored-By: Name <mail>.

Title Case of Headings

The hook puts each ATX heading (# to ######) in Title Case in the same pass. The rule follows the Chicago style of the repository:

• Articles, coordinating conjunctions, and prepositions stay in lowercase.
• The first word, the last word, and the word after a colon get a capital letter.
• Each part of a hyphenated word gets a capital letter, such as Add-On.
• A code span, a link target, a tag, and a URL do not change.
• A word with a mixed case, a digit, or a dot does not change.

The rule does not apply inside a fence, an indented block, or the front matter.

See Also

• Guard
• Controls
• Off Switches