Plain-text normalization

Contract

Enforces three fixed plain-text conventions when cleaning up prose without rewording it: (1) every sentence starts with a capital letter, (2) exactly one space separates one sentence from the next, and (3) no line carries trailing whitespace. Apply whenever asked to tidy, clean up, or make presentable a block of raw text — a pasted note, chat transcript, dictation, or scraped paragraph — where the job is to fix spacing and capitalization, not to rewrite the wording. (Trailing spaces below are shown as ␣ so they are visible.)

Rules

1. Sentence-initial capitalization. The first alphabetic character of every

sentence is uppercase. A sentence begins at the very start of the text and immediately after every sentence-ending ., ?, or !. Uppercase that first letter even if the input typed it lowercase. Do not change the case of any other word (leave existing proper nouns and mid-sentence words as-is).

1. Exactly one space after a sentence-ending period. Between a period that

ends a sentence and the first character of the next sentence there is exactly ONE ordinary space:

• Never ZERO — a period glued to the next word (done.Next, done.next) gets

a single space inserted (done. Next).

• Never TWO OR MORE — a run of spaces (done. Next, done. Next, or a tab)

collapses to one (done. Next). This is the modern single-space-between-sentences convention, not the typewriter two-space habit. The same one-space rule applies after a sentence that ends in ? or !.

1. No trailing whitespace. Strip every space and tab that sits at the end of a

line (before the newline) and at the very end of the text. A blank line becomes truly empty — no spaces on it. This never removes meaningful content, only the invisible run-off at line ends.

1. Preserve the wording. Change ONLY capitalization and whitespace. Do not add,

drop, reorder, or reword sentences; do not touch internal punctuation, numbers, or line breaks other than trailing-space removal. The output is the same text, correctly cased and spaced.

Worked examples

Rule 1 — a lowercase sentence start is capitalized (both the first word and the one after a period).

BEFORE:  the kettle boiled. we brewed a fresh pot.
AFTER:   The kettle boiled. We brewed a fresh pot.

Rule 2 (missing space) — a period glued to the next sentence gets one space.

BEFORE:  Add the flour.Stir gently until it thickens.
AFTER:   Add the flour. Stir gently until it thickens.

Rule 2 (extra spaces) — two spaces after the period collapse to one.

BEFORE:  The trail was steep.  The summit view repaid every step.
AFTER:   The trail was steep. The summit view repaid every step.

Rule 1 + 2 combined — glued AND lowercase.

BEFORE:  the garden needs water.the tomatoes are wilting.
AFTER:   The garden needs water. The tomatoes are wilting.

Rule 3 — trailing spaces at line ends are stripped (␣ = a trailing space).

BEFORE:  Pack the tent.␣␣
         Fill the water bottles.␣
AFTER:   Pack the tent.
         Fill the water bottles.

Rule 4 — spacing/case only; wording is untouched (a ? sentence too).

BEFORE:  did the ferry leave?we missed it by minutes.
AFTER:   Did the ferry leave? We missed it by minutes.

Edge cases & exceptions

• Abbreviations are not sentence ends. A period inside e.g., i.e., etc.,

Dr., Mr., U.S., a.m. does NOT start a new sentence: keep the following word's case unchanged and do not force a capital. we ship many formats, e.g. json and yaml. → We ship many formats, e.g. json and yaml. (leading we capitalized; json stays lowercase).

• Decimals and version numbers. The dot in 3.14, v2.0, or 1.5 cups is not

a sentence terminator — never insert a space and never capitalize after it.

• Dotted tokens. Dots inside config.yaml, example.com, or a.b.c are part

of the token; do not treat them as sentence breaks.

• Ellipsis. Leave ... (or …) intact — do not split it into separated

periods and do not insert spaces between the dots.

• Already-correct text. If a sentence is already capitalized and single-spaced,

leave it exactly as-is; do not "re-fix" what already conforms.

• First line of the text. Its opening letter is capitalized like any sentence

start, even though no period precedes it.

Do / Don't

• Never leave a sentence starting with a lowercase letter. Always uppercase

the first letter of every sentence.

• Never keep two-or-more spaces after a sentence-ending period. Always

collapse them to exactly one.

• Never leave a period glued to the next sentence. Always insert one space.
• Never leave trailing spaces or tabs at the end of a line. Always strip

them.

• Never reword, reorder, or delete the author's sentences. Always change

only capitalization and whitespace.

• Never treat an abbreviation dot or a decimal point as a sentence boundary.

Always limit the sentence-boundary rules to real sentence ends.

Common mistakes

• Mirroring the input's spacing: passing through the two spaces after a period that

the source used instead of normalizing to one.

• Failing to split a glued word.Word, leaving the two sentences run together.
• Capitalizing the first sentence but missing the capital on later sentences that

followed a period on the same line.

• Leaving invisible trailing spaces at line ends because they are not visible in

the rendered text.

• Over-correcting: capitalizing the word after e.g. / Dr. / a decimal, or

inserting a space inside 3.14 or config.json.

• Silently rewording or "improving" the sentences instead of only fixing spacing

and case.

Quick checklist

• ] Every sentence starts with a capital letter (first sentence and each one

after a ., ?, or !).

• ] Exactly one space after each sentence-ending period — no glued periods, no

double spaces.

• ] No trailing spaces or tabs at any line end.
• ] Wording, order, numbers, and internal punctuation unchanged.
• ] Abbreviation dots, decimals, and dotted tokens not treated as sentence ends.