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The CDN URL is the API. Any combination of parameters produces a deterministic URL with a stable cache key — same params, same cached bytes worldwide.
Each guide below opens with live output examples, then documents the params for that transform family.

Forma AI & ML

Background removal, generative replace, object removal, text-to-image, and outpaint.

Watermarks

Single marks, tiled grids, blend modes, rotation, and anchor positions.

Face and plate privacy

Face blur, face pixelation, license-plate redaction, and coordinate-based region privacy.

Resize, crop & fit

Width, height, aspect ratio, fit modes, and smart gravity crops.

Text overlays

Dynamic OG cards, badges, multiline text, stroke, and custom fonts.

Adjustments & effects

Brightness, contrast, blur, sharpen, auto-enhance, and auto-compress.

Format & delivery

Format negotiation, progressive JPEG, content-aware quality, client hints, and metadata stripping.

Download

Force browser downloads with dl and Content-Disposition attachment headers.

Vector & SVG

Raster-to-SVG tracing and SVG input sanitization.

Canvas, trim & masks

Padding, borders, rounded corners, alpha trim, and image masks.

Video transforms

Poster frames, clip trimming, transcode, and animated GIF output.
For focal-point workflows and /api/images/analyze, see Smart cropping & image analysis.

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Parameter reference

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Size, crop, and focal

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Format and delivery

See Format & delivery and Download.

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Canvas, trim, and masks

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Vector and SVG

See Vector & SVG.

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Watermarks

See Watermarks.

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Text overlays

See Text overlays.

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Adjustments and effects

See Adjustments & effects.

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Face and plate privacy

See Face and plate privacy.

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Colour palette

See Smart cropping & image analysis.

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AI and ML

See Forma AI & ML.

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Video and documents

See Video transforms.

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How caching works

Every URL is deterministic. The endpoint sets long-lived immutable cache headers and varies on Accept and Save-Data:
Convertly uses two shared cache layers. A visitor-facing edge cache serves hot responses close to the requester. A persistent variant cache stores successful renders so a cold edge in another region can usually refill without re-encoding the source. Only a miss in both layers reaches the transform origin. For a stable set of responsive image URLs, a 90-99% edge hit ratio is realistic after warm-up. Persistent variant hits further reduce transform-origin traffic when a regional edge is cold. Responses expose cache diagnostics that work in a browser network panel or with curl -I:

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Realistic cache ratios

The 95% number is achievable, not guaranteed. A few honest factors:
  • Edge caches are regional. A globally popular image must warm at more than one edge. The persistent variant layer prevents most regional cold fills from repeating the original transform.
  • LRU eviction. Edge caches evict less popular URLs under memory pressure. Long-tail content re-fetches more often than hot URLs.
  • Cache-busting URLs. Anything like ?v=${Date.now()} collapses the cache ratio to nearly zero. Use a content hash or an asset revision that changes only when the source bytes change.
  • Too many responsive widths. Every unique width is a separate variant. Define a small width set that matches your layout instead of generating a new width for every device pixel value.

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What counts as a delivery

An origin request is a request that misses both Convertly cache layers and reaches the transform or source origin. These do not consume the origin-request allowance:
  • Repeat hits served by an edge cache.
  • Persistent variant hits used to refill a cold regional edge.
  • Browser cache hits.
  • Service worker cache hits.
The first request for a new (file, canonical params, negotiated format) variant normally counts. Later regional edge fills can reuse its persistent render. A request counts again only when both cache layers miss or a purge intentionally removes the reusable variant.