Interactive embeds

Same id as a saved chart, different URL. /e/{id} renders an interactive HTML page – tooltips, legend toggle, responsive.

Every chart you save via POST /api/charts mints two URLs from one id:

/c/{id} – the static image you embed in emails and Markdown.
/e/{id} – an interactive HTML page you drop into an <iframe>.

Same config, same visual quality, different medium. Use the embed when the chart lives in a web product or dashboard and your readers expect to hover, scan series, and toggle legend items.

Embedding

The embed URL works inside any iframe on any origin:

<iframe
  src="https://szum.io/e/abc123"
  loading="lazy"
  scrolling="no"
  style="width: 100%; aspect-ratio: 16/10; border: 0"
></iframe>

Set aspect-ratio to the dimensions your saved chart was sized to. The runtime is container-driven – it re-renders to match the iframe at any width.

What's interactive

Hover. A tooltip follows the pointer. For lines and stacked areas the tooltip is x-aggregated – one tooltip per unique x, with all visible series listed at that x. A 1px vertical indicator marks the active x. For bars, dots, and pies the tooltip names the datum directly under the cursor.
Legend toggle. Click any legend item to hide its series. The chart re-packs immediately – stacked bars rearrange as if the hidden series wasn't there. Click again to bring it back.
Responsive. The runtime watches the iframe with a ResizeObserver and re-lays out on every change. Drag the parent window and the chart follows.
Touch. Tap and drag to scrub the chart; the tooltip follows the touch. Lift to dismiss. Vertical page scrolling is preserved – the chart only captures horizontal gestures.

Same primitive as saved charts

The embed route shares everything with /c/{id}:

Same opaque 16-byte id.
Same storage and ownership. Available on Free and Pro.
Same 30-day grace period when a Pro account downgrades to Free – URLs return 403 during the grace window, then 404 after deletion. Free-from-the-start accounts serve normally.
Same DELETE /api/charts/{id} to revoke a single chart.
Same per-config size limit of 50 KB.

Only cache-miss loads of /e/{id} count – one render against the creator's monthly quota, the same meter that covers /c/{id}. CDN cache hits are served from the edge for free; there is no separate per-view charge.

In practice, with s-maxage=86400 + stale-while-revalidate=86400, render runs only on the first hit per cache window per region. A chart in an article read by 10,000 viewers across regions typically generates only ~20–40 renders per day at peak (one per region per cache cycle); the CDN absorbs the rest at no cost.

Once the page loads in a viewer's browser, every subsequent local interaction (hover, resize, legend toggle) runs entirely on the client and never reaches origin – no extra cost.

Theming

The embed inherits the chart's theme. editorial looks like editorial; dark looks like dark – page background, tooltip surface, legend swatches, and the x-indicator all derive from the resolved theme. If you need a custom palette, use themeOverrides in the saved config.

Attribution

Free embeds carry the same small "made with szum" credit as the static image – rendered inside the chart by the same pipeline, so the band and spacing match exactly. In the embed it's also a real link: the credit group is wrapped in an <a>, so clicking it opens szum.io (in the static image it's just pixels). Pro embeds omit it by default (set attribution: true in the saved config to keep it).

Errors

Status	Meaning
`308`	Request URL had a query string. Permanent redirect to the canonical bare `/e/{id}`; browsers and `<iframe>` loaders follow automatically. Cached for 1d.
`403`	Chart owner is on a paused plan (post-downgrade grace period)
`404`	Chart deleted, never existed, or grace period expired
`413`	Config too large at save time (won't surface on embed; surfaced at `POST /api/charts`)
`429`	Per-IP burst rate limit on origin hits (cache misses only). Includes `Retry-After`. CDN cache hits bypass the limiter entirely.
`503`	Storage temporarily unavailable – retry after `Retry-After: 2`

All error responses set Cache-Control: private, no-store, so a transient blob outage or post-downgrade 403 isn't edge-cached.