Carousel Maker

Turn notes, code or screenshots into a swipeable carousel — PDF for LinkedIn, PNGs for Instagram.

Runs locallyWorks offlineShare link carries settings, never your data

Your writing

# Three things I got wrong about caching

A thread on the mistakes that cost us a weekend.

---

## 1. TTL is not a cache strategy

Setting an expiry says when data becomes wrong. It does not say what to do
about it. Every stale read still hits your origin at the same moment.

---

> Stampedes are a concurrency problem wearing a caching costume.

---

## 2. The fix is one lock

```ts
const key = `lock:${id}`;
if (await redis.set(key, 1, "NX", "EX", 5)) {
  const fresh = await origin(id);
  await redis.set(id, fresh, "EX", 300);
}
```

---

# Cache what is expensive, not what is slow

They are not the same thing.

--- starts a new slide, # makes a heading, > pulls a quote out, and a fenced block becomes a code slide of its own.

Add picturesScreenshots, photos, charts — they stay in this tab like the writing does.

ShapeFooter line

BackgroundTextAccentNumber the slides

6 slides

LinkedIn takes the PDF as a document post; Instagram takes the PNGs. Both are drawn here, in this tab — nothing you write is uploaded.

Send output toQR Code Generator Password Generator Focus Timer Build a workflow from thisOutput stays on this page until you send it.

Frequently asked questions

Which file do I need — PDF or PNGs?

PDF for LinkedIn: its document posts take a PDF and turn each page into a swipeable card, which is why the landscape 4:3 shape is offered. PNGs for Instagram, which wants square or 4:5 images uploaded as a gallery. Both come from the same drawing, so the deck is identical either way; only the container differs.

How big is the download?

Small, on purpose. A four-slide deck with two full-size phone photographs in it comes out around 420 KB as a PDF. Photographs are stored and saved as JPEG and shrunk on import to the largest size a slide can use; text slides stay PNG so the type stays sharp. The same deck saving every card as a PNG would be several megabytes.

Is there a watermark or an export limit?

No, and there is no mechanism for one. The slides are drawn on a canvas in your own browser, so there is no render server whose time has to be paid for and nothing to meter. Make as many as you like.

Will the download look exactly like the preview?

Yes, and that is the point. Both come from one drawing routine, run at the same pixel size — the preview is not a mock-up of the export, it is the export at screen scale. The one thing that can differ is the typeface: the slides use the fonts this site loads, so if one has not finished loading when you export, the browser substitutes. Give the page a moment on first visit.

What happens to a slide with too much on it?

Text is wrapped to the measure and the card is filled from the top. If a slide genuinely holds more than it can show, the overflow is dropped rather than drawn off the edge — but that is a sign the slide wants splitting. Put a line of dashes in the middle of it.

Can I use my own fonts or a logo?

Not fonts, not yet. Pictures, yes — attach them and place them with a Markdown image line. The colours are yours too, and the footer line carries a handle or a domain, which covers most of what branding is for on a carousel. Uploaded typefaces are the obvious next step and are not built.

Does it post to LinkedIn or Instagram for me?

No. It makes the file; you post it. Publishing needs an account connection and a platform API, neither of which exists here — and an API that changes under you is the thing most likely to break a tool like this overnight.

Pro tips

Write the post first and split it afterwards. Prose you drafted as prose reads better on a card than sentences written to fill one.
Put the sharpest line on its own slide with an angle bracket. A pull quote between two dense cards is what gives a reader somewhere to breathe, and it is the slide most often screenshotted.
Keep code slides to about ten lines. Longer and the type shrinks to fit, which is legible on a laptop and not on the phone most people will swipe it on.
Use the footer line for the one thing you want carried with a screenshot — a handle or a domain. It sits in the same place on every card so it survives cropping.
Set the accent to your own colour before you export. It is the only mark every slide in the deck shares, and it is what makes a run of them read as one carousel rather than five separate images.

About Carousel Maker

A carousel is a deck of images, and the hard part is not making them pretty — it is that the preview and the export are usually two different pieces of code, so the deck you approved is not quite the deck you posted. Here one routine draws both, at two scales, which is why the card on screen is the file. The source is the format you already write in: a line of dashes between slides, a hash for a heading, a fence for code.

A carousel is a stack of images that a reader swipes, and the platforms are strict about what they accept: LinkedIn takes a PDF as a document post, Instagram takes square or 4:5 images, and both scale whatever you give them to fit. So the useful question is not what the design tool can do, it is whether the file you download is the one you approved on screen. Here the preview and the export call the same drawing routine at two different scales — the card you are looking at is the file, not a representation of it.

The source is the format people already write in rather than a new one to learn. A line of three dashes starts the next slide, because that is what a rule means in Markdown and what a divider means in a note. A hash makes a heading; a heading with nothing under it becomes a title card, and a heading with a paragraph under it becomes that paragraph with a heading, which is a different-looking slide. An angle bracket pulls a line out as a quote, set larger and in the accent colour, for the sentence worth stopping on. A fenced block becomes a code slide of its own, because a snippet sharing a card with prose is unreadable at the size these are viewed at.

Pictures go in the same way the text does. Attach a screenshot and write a Markdown image line where you want it, naming the file — it always takes a slide of its own, because a picture sharing a card with a paragraph is too small to read on the phone most people swipe these on. It is drawn to cover the card and cropped rather than squashed, since a stretched screenshot looks worse than a tight one and every platform crops a carousel to its own shape anyway; a caption sits in a bar along the bottom rather than over the image, because text laid over a picture you have not seen is a contrast gamble. Name a file you have not attached and the slide says so, instead of coming out blank and looking like a broken export.

Each slide is saved in the format it deserves, which is what keeps a deck with photographs in it a few hundred kilobytes rather than tens of megabytes. A card of flat colour and sharp type is a PNG, where text edges stay crisp; a card that is a photograph is a JPEG, where a PNG would be fourteen times the size for no visible gain and JPEG’s ringing has no type to ring around. Attached pictures are also shrunk on the way in to the largest size any card can actually use — a phone photograph is four thousand pixels wide, and everything past sixteen hundred is thrown away at draw time regardless, after being carried through every redraw and into the download.

Code is treated differently from prose on purpose. Prose is re-wrapped to the measure, and a word too long for the line — a URL, a long identifier — is broken rather than allowed to run off the edge, since silently overflowing looks like a bug in the export and is only noticed after posting. Code is never re-wrapped, because a broken line of code is wrong rather than narrow; it is fitted by reducing the type size instead, down to a floor that stays legible on a phone. Indentation is kept exactly as written.

Everything is drawn on a canvas in the tab. That is a privacy property — a draft about an unreleased feature or a client's numbers is never sent anywhere — but it is also why there is no watermark and no export limit: there is no render server whose time has to be rationed. The PDF is built with pdf-lib in the same tab, one page per slide at the exact pixel size, and the PNGs are packed into a ZIP written here too.

What it does not do is lay out for you. There is no drag handle, no image placement and no template gallery: the deck is a consequence of the writing, so editing the post edits the deck. That is the right trade for a thread you have already drafted and the wrong one for a designed brochure — if you need to position things, a design tool is the honest answer.

Common use cases

Turning a thread you drafted in a notes app into a LinkedIn document post without retyping it into a design tool.
Posting a code snippet as an image, with the indentation intact, instead of a screenshot of an editor at whatever zoom it happened to be.
Making a set of slides from release notes or a changelog entry, where the writing already exists and the deck is just its shape.
Repeating a format weekly — same shape, same colours, different words — by keeping the link, which carries the settings but never the writing.
Drafting a post about something unreleased, where uploading it to a third-party renderer to make pictures is not an option.

How it comparesCanva and Figma will beat this on design: templates, image placement, real typography controls, and a team library. If you are making a designed brochure, use one of them. The dedicated carousel makers — Taplio, AuthoredUp, Contentdrips — add scheduling, analytics and LinkedIn preview, which this has none of, and most render on a server, which is why they can watermark free exports and meter them. What this does better is narrower: your writing is the source of truth, the preview is the file, there is no sign-up, no watermark and no export cap, and nothing you type is uploaded. If your post is already written and you want it as slides in thirty seconds, that is the trade worth taking.