All rules

Dates written two ways

date-format-consistencyon by default (info)Japanese / English

Dates written two ways in one document, as "2026-10-02" and "October 2, 2026"

Example

Flagged
Registration opens on October 2, 2026 and closes on October 9, 2026. Results are sent on 10/16/2026.
What chaff prints
1:90 The date "10/16/2026" is written differently from 2 other dates in the document (such as "October 2, 2026")
Fixed
Registration opens on October 2, 2026 and closes on October 9, 2026. Results are sent on October 16, 2026.
What chaff prints
no finding

How to fix

Write every date in the document the same way.

Why it matters

One document writing "2026-10-02" in one place and "October 2, 2026" or "10/2/2026" in another makes the reader check whether the dates are the same kind, and 10/2 may be read as October 2 or 10 February. The mix usually comes from a pasted or later-added passage. chaff does not pick a style; it points at the minority. Only dates with a year, a month and a day are compared. Month names and eras are in each language's lexicon.

What it does not flag

Year-only and month-day dates, numbers inside URLs and versions (/2026/10/02/, 1.2026.10), and dates in code are not compared. When the minority is more than a third of the dates, the document is taken to use two styles on purpose (ISO in tables, long dates in prose) and nothing is reported, nor when the two commonest styles are tied.

Turning it off or relaxing it

Silence this one spot (in the document)
<!-- stet: date-format-consistency — reason -->
Relax it for the team (the reason is kept as a comment in chaff.yaml)
npx chaffjs relax date-format-consistency --why "reason"
Turn it off for the team (chaff.yaml)
rules: date-format-consistency: off
Technical details
Layer
L1
Status
stable
Severity
info
Languages
Japanese and English
Suited to
business, technical, blog, legal, docs, academic, literature, speech

Levels

Set a level for this rule under rules in chaff.yaml. With nothing set, it runs at the level its genre gives it (see By genre below).

strictreported while the minority style is 49% of the dates or less
normalreported while the minority style is 34% of the dates or less
relaxedreported while the minority style is 20% of the dates or less

By genre

Runs by default in
technical/spec, technical/readme, blog/tech, blog/essay, blog/owned-media, business/proposal, business/report, business/email, business/press-release, business/meeting-notes, legal/contract, legal/statute, legal/judgment, legal/patent, docs/manual, docs/faq, docs/glossary, academic/paper, literature/fiction, literature/essay, literature/poetry, literature/play, speech/address, speech/transcript

Genres

Message

The date "{written}" is written differently from {count} other dates in the document (such as "{example}")

Rewrite depth (chaff fix-plan --depth): light — words and sentences; the structure and the voice stay

This page is built from the rule's definition file:packages/chaff/rules/date-format-consistency.yaml