AI Caption Rewriter — improve, shorten, change tone, translate VI↔EN
Paste an existing caption → AI generates 3 rewrites in 7 modes: general improvement, shorten, lengthen, change tone, fix grammar, translate VI→EN, translate EN→VI. Realtime streaming, free 20/hour.
Rewrite mode
Why use this tool
Improve, shorten, lengthen, change tone (6 tones), fix grammar, two-way translation — all in one place.
fix-grammar mode automatically replaces formal Sino-Vietnamese with natural Vietnamese, with cultural awareness.
Unlike Google Translate, AI preserves tone + emoji + hashtags when translating VI↔EN. Reads native.
How to use
- 1Paste the old caption (max 2000 chars).
- 2Pick mode: Improve / Shorten / Lengthen / Change tone / Fix grammar / Translate VI→EN / Translate EN→VI.
- 3If 'Change tone': pick a target tone (playful, Gen Z, professional...).
- 4Click Generate → 3 rewrite variations stream in realtime.
- 5Pick a favorite, copy, paste into FB/TikTok/IG.
Caption rewriter — why need it?
Writing from scratch is hard, but rewriting an existing caption for a different audience/platform/purpose is hard too. Rewriter solves: caption that works on FB → need a TikTok-friendly shorter version? Caption in Vietnamese → need English for international audience?
7 modes cover most use cases: 'Improve' keeps intent, rewrites more naturally. 'Shorten' trims 50-70% for TikTok. 'Lengthen' adds detail for longer FB posts. 'Change tone' shifts formal → casual. 'Fix grammar' removes typos + replaces stilted Sino-Vietnamese. Translate modes keep intent + tone.
Streaming makes UX fast — 3 variations in 3-5 seconds vs 10s wait.
- ✓7 rewrite modes in 1 tool
- ✓3 diverse variations per generation
- ✓Streaming response realtime
- ✓VI + EN support
- ✓Translation keeps tone + emoji + hashtags
- ✓Auto-fix stilted Sino-Vietnamese
- ✓Max 2000 char input
- ✓Rate limit 20/hour/IP
Use cases
Long FB caption → 'Shorten' mode → TikTok-ready punchy.
'Professional' caption → 'Gen Z slang' to target teens.
English caption from global brand → translate to natural Vietnamese.
Draft caption fast, scan via 'Fix grammar' before posting.
1 caption → 3 improve variations → A/B test engagement.
Year-old caption → 'Improve' to repost with fresh form.
Tech
Backend /api/ai/rewriter POST {text, mode, tone?}. Validate text ≤2000, mode ∈ 7 values. When mode='change-tone', tone is required.
System prompt built dynamically: MODE_NOTES[mode] + TONE_NOTES[tone] (only on change-tone). Streaming Anthropic Haiku 4.5, temperature 0.7.
3 variations numbered 1. 2. 3. parsed via regex /^\d+\.\s/.
FAQ
Does the rewrite change meaning?
'Improve' keeps the main intent, only changes phrasing. 'Change tone' keeps intent but shifts style. Only 'Lengthen' may add details (examples, CTA).
Is VI→EN translation accurate?
AI uses natural English style (not word-by-word). However, specific cultural nuance may adapt (e.g. 'chốt đơn' → 'order now' instead of literal).
Input length limit?
2000 chars max. Captions are usually short so plenty. Split if longer.
How is 'Fix grammar' different from browser spell-check?
Spell-check fixes typos. AI understands context: replaces stilted Sino-Vietnamese with natural Vietnamese, completes fragmented sentences without changing meaning.