An Instagram caption generator writes the words under your post from a short brief: what the photo shows, the news or story behind it, and what you want people to do next. In Toybox AI, that's AI Writer with Type set to "Social post". It writes text captions, not the subtitles that play over a Reel, and it can't see your photo, so you describe the picture in a line. Below are caption formulas by post type, briefs to paste, Instagram's limits, and the gaps to know about.
What an AI caption generator for Instagram can write
Each AI Writer run gives back a single piece of text, which can hold one caption or several options.
- A product post caption with the price, the size or color, and where to buy it.
- An event reminder with the weekday and date, time, place, and how to RSVP.
- A carousel caption that tells people to swipe and says what the last slide gives them.
- A Reel caption plus a hook line you type onto the video in Instagram's editor.
- A behind-the-scenes caption built on one real detail from your day.
- Alt text for the image. Instagram writes automatic alt text with object recognition, and you can replace it under Accessibility with one sentence written from your notes.
- Three options in one run, each with a different first line, so you pick instead of rewriting.
- Your five hashtags, chosen from words you give it.
Instagram caption rules to write for
These are the limits a caption has to fit, as of September 2026.
| Rule | Limit | Source |
|---|---|---|
| Caption length | Up to 2,200 characters | Meta's developer documentation for Instagram posts |
| Hashtags | Up to 5 per post or reel | Instagram's @creators account, December 18, 2025 |
| Alt text | Automatic by default; replace it under Accessibility before or after posting | Instagram Help Center |
Meta's developer documentation still lists 30 hashtags for captions published through its API, but Instagram's own guidance since December 18, 2025 is 5. Write to the lower number. For the image itself, the Instagram post size guide covers feed and Story shapes, and the AI Instagram post maker makes the post image to go with the caption.
Caption formulas by post type
A caption does three jobs: a first line that makes sense on its own, a middle with the facts, and a last line that asks for one action. Here's how that looks for common posts (all names and details are fictional).
| Post type | First line | Middle | Last line |
|---|---|---|---|
| New product | "Our pumpkin rye is back, and it sells out by 10." | "Baked Fridays and Saturdays only, $9 a loaf." | "Order ahead through the link in bio." |
| Event | "Sunday, October 18: free bike tune-ups in our lot." | "11 AM to 3 PM at 14 Gear Street. Bring any bike, we check brakes and tires." | "Comment BIKE and we'll save you a slot." |
| Sale | "Every sweater is 25% off until Sunday." | "In store and online, while sizes last." | "Tap the product tags to shop." |
| Behind the scenes | "This is what 400 tulip bulbs look like before breakfast." | "One detail from the day, in two sentences." | "Which color should we plant next?" |
| Carousel tip | "5 ways to keep cut flowers fresh for a week. Swipe." | "One line per slide, in the same order as the slides." | "Save this for your next bouquet." |
| Reel | "Watch us fix a flat in 60 seconds." | "The one tool you need, named." | "Follow for a repair tip every Tuesday." |
A question in the last line is fine as a call to action; keep it to one.
Caption briefs for AI Writer
Choose "Social post" under Type. Pick "Short" under Length for a single caption, and "Medium" when the brief asks for three options, since Short returns only a few sentences. Then paste a brief into "What should we write?" and replace the details with your own.
For a product post:
Write 3 Instagram caption options for a bakery post. Photo: a stack of pumpkin rye loaves on a wooden board. Facts: pumpkin rye is back for the fall, baked Fridays and Saturdays only, $9 a loaf, usually sold out by 10 AM at Rye and Ramble Bakehouse, 22 Mill Road. Voice: warm, first person plural, no exclamation points. Each option: a first line under 12 words, two short lines of detail, and end with "Order ahead through the link in bio." Add 5 specific hashtags at the end.For an event reminder:
Write an Instagram caption reminding followers about free bike tune-ups at Spokenettle Bike Repair, 14 Gear Street, on Sunday, October 18, 11 AM to 3 PM. We check brakes, tires and chains on any bike, no appointment needed, and kids' bikes are welcome. Start with the date. Keep it under 60 words. End with: "Comment BIKE and we'll save you a slot." No hashtags.For a carousel:
Write an Instagram carousel caption for a 6-slide post called "6 ways to keep cut flowers fresh for a week" from Tansyholm Florals. Slides: recut stems at an angle, change the water every two days, strip leaves below the waterline, keep them away from fruit, use the flower food packet, keep the vase out of direct sun. The caption should say to swipe, list the six tips in one line each in the same order, and end with "Save this for your next bouquet."For a Reel:
Write an Instagram Reel caption and a separate hook line for the video. The Reel shows a mechanic fixing a flat bike tire in about 60 seconds using only tire levers and a pump. The hook line goes on screen in the first second: 8 words or fewer. The caption: two lines explaining the steps, then "Follow for a repair tip every Tuesday." Label them Hook and Caption.For alt text:
Write alt text for an Instagram photo, one sentence under 25 words, describing only what is visible. The photo: a florist's hands wrapping a bouquet of orange tulips and white ranunculus in brown paper on a wooden workbench, with scissors and twine beside it.More caption, Reel and content-idea prompts are in the library of ChatGPT prompts for Instagram, and they run in AI Writer too.
Tips for better AI captions
- Give facts, not adjectives. "$9 a loaf, Fridays and Saturdays" is something a caption can say. "Delicious and amazing" leaves the draft with nothing but more adjectives.
- Ask for three first lines. The first line carries the post. Choose the best of three rather than editing one.
- Say who's talking. "We" for a shop, "I" for a maker, and whether exclamation points are allowed. AI Writer has no tone control, which is why the voice has to be written into the brief.
- Copy the image text word for word. If the post image says "Sunday, October 18", the caption says the same weekday and date.
- Put the five hashtags last. Name the ones you already use, plus your town or niche, and cut any that don't describe the post.
- Read it on your phone. Paste the draft into Instagram's caption box, look at it on screen, and cut any line that repeats the image.
Instagram caption generator from a photo
AI Writer works from text only, so it can't look at your picture. Three routes get you a caption that fits a photo:
- Describe the photo in the brief. One plain line ("a stack of pumpkin rye loaves on a wooden board") is enough for AI Writer to write around it.
- Use a tool that reads images. ChatGPT accepts an attached, pasted or dragged-in image; tell it what the post is for and what to write, not only "caption this".
- For pet accounts, try Pet Thoughts. Upload the pet photo and Toybox writes 2 to 4 funny, family-friendly sentences in the pet's voice, currently for 5 credits on the Free plan. It's for fun, not a read on what your pet feels.
Limits to know
- It can't see your photo. Describe it, or use one of the image routes above.
- It doesn't make video subtitles. "AI caption generator" also means tools that add on-screen text to a video. AI Writer writes post text only; use a video editor's captions feature for subtitles.
- Nothing is formatted for Instagram automatically. There's no platform setting, so write the voice, length, structure and number of hashtags into the brief, or write "No hashtags".
- No caption history. Each run stands alone and isn't saved to a Recent list, so paste your best briefs into your notes app to reuse.
- It won't fact-check. Read every date, price and address before you post, the same as you would on the post image.
How to write an Instagram caption in AI Writer
- Go to AI Writer and sign in. New accounts get 20 free credits.
- Choose "Social post" under Type, then "Short" under Length for one caption or "Medium" for three options.
- Type or speak your brief into "What should we write?": what the photo shows, the facts, the voice, the call to action and the number of options. There's room for 2,000 characters, and the mic works in Chrome, Edge and Safari.
- Tap "Write it". The caption is usually ready in about 10 seconds.
- Read every date and price, choose the option you like, and trim it.
- Tap Copy and paste the caption into Instagram, with your hashtags at the end.
AI Writer currently costs 5 credits per run on the Free plan; see Toybox pricing for top-ups. Post images, short videos and scheduling are covered in AI tools for social media.