Name: AI Alt Text API · WCAG Image Descriptions · 130+ Langs
Brand: reddit-intel
SKU: api-reddit-intel-ai-alt-text-and-image-description-api
Availability: InStock
Author: API Market

# AI Alt-Text & Image Description API

**Generate WCAG-compliant alt-text and SEO-ready image descriptions for any image URL — in 130+ languages, in one API call.**

Stop writing alt text by hand. Submit an image URL, receive **two outputs in one request**: a concise alt-text string ready for the HTML `alt` attribute (max 125 characters, accessibility-optimised) and a 1–3 sentence description suitable for image captions, product paragraphs, or social posts. Powered by Google Gemini 2.5 Flash, returning in 1.5–3 seconds on a fresh image, **under 200 ms** from the built-in content cache.

## Why this API

- **Two outputs per call.** Most APIs need two requests for alt-text and a longer caption. We give you both — accessibility tag *and* descriptive caption — from one call.
- **130+ languages natively.** Pass any BCP-47 code (`en`, `es`, `fr`, `de`, `ja`, `zh-CN`, `ar`, `pt-BR`, `hi`, `tr`...) and the model writes the output in that language directly. No separate translation step. No extra cost.
- **Three writing styles for different jobs.** `descriptive` (general accessibility, default), `seo` (keyword-rich, optionally accepts a target keywords array), `ecom` (product-listing tone for online stores).
- **Built-in image caching, free.** Identical images return instantly on repeat. Bulk-process a 10,000-product Shopify catalog without re-paying for duplicate images. The cache is keyed by SHA-256 of image bytes, so it correctly catches CDN URL variations of the same file.
- **WCAG 2.2-aligned output.** Alt-text is concise, factual, screen-reader optimised. No "image of..." prefixes. No speculation about brand or context not visible in the image. No marketing fluff to strip out.
- **Safe by design.** Every URL is fetched, validated, and SSRF-blocked before inference. Image format and size are verified by magic-byte check, not just by extension. Failed requests return clear JSON errors and **never count against your billable quota** — only HTTP 200 responses consume calls.

## Common use cases

- **E-commerce stores** (Shopify, WooCommerce, BigCommerce) auto-generating alt text on product upload
- **WordPress and CMS blogs** bulk-processing historical image libraries that never had alt text — improving accessibility scores instantly
- **Accessibility compliance teams** meeting WCAG 2.2 Success Criterion 1.1.1 (Non-text Content) without hiring copywriters
- **SEO agencies** productising image-search optimisation as a service — keyword-aware alt text at scale
- **Multilingual publishers** needing one-step caption translation across international editions
- **Social media schedulers** generating post-caption suggestions automatically from uploaded creatives

## What you save

Standalone alt-text services charge around **$0.04 per image**. Processing 50,000 product images that way costs $2,000. Same job, same underlying model quality, **a fraction of the cost here** — depending on your subscription plan. Plans start from $9.99/month for 5,000 calls; overage at $0.001–$0.005/call on soft-limit plans.

## Style modes

The optional `style` parameter changes the writing tone of the output. Same image, three different outputs depending on what you need:

- **`descriptive`** (default) — general-purpose accessibility output. Factual, screen-reader optimised, no marketing language. Use for blog images, news photography, generic illustrations.
- **`seo`** — keyword-rich output woven naturally (no keyword stuffing). Optimised for image-search ranking. Accepts an optional `keywords` array to target specific search terms.
- **`ecom`** — product-listing tone for e-commerce. Describes product, material, colour, and visible features in shop-page language. Does NOT invent brand names or specifications not visible in the image.

## Multilingual output

Pass any BCP-47 code in `lang` and the model generates output natively in that language — there's no separate translation step. Quality is materially better than running English output through a translator.

Languages tested in production include: English (`en`), Spanish (`es`), French (`fr`), German (`de`), Italian (`it`), Portuguese (`pt`, `pt-BR`), Dutch (`nl`), Polish (`pl`), Russian (`ru`), Japanese (`ja`), Korean (`ko`), Chinese Simplified (`zh-CN`), Chinese Traditional (`zh-TW`), Arabic (`ar`), Hindi (`hi`), Turkish (`tr`), Vietnamese (`vi`), Thai (`th`), Indonesian (`id`), Hebrew (`he`), Greek (`el`), Czech (`cs`), Romanian (`ro`), Hungarian (`hu`), Ukrainian (`uk`), Swedish (`sv`), Finnish (`fi`), Norwegian (`no`), Danish (`da`), plus 100+ others.

If your target language isn't listed but is a real BCP-47 code, try it — coverage is broader than the tested list.

## Image caching

When the same image is submitted again with the same `lang` and `style`, the cached response returns in under 200 ms.

- **Keyed by SHA-256 of the image bytes**, not by URL — different URLs serving the same file all hit the same cache entry. CDN variants, mirror hosts, signed URLs of the same image all share the cache.
- **30-day rolling TTL** — entries are evicted 30 days after last access.
- **Per-image, not per-consumer** — you cannot retrieve another consumer's cached results unless you submit the same image.
- **Does not affect billing** — calls count against your monthly quota whether served from cache or freshly generated. Cache benefits you with ~15× faster response, not lower cost.

Cache hits return `"cached": true` in the response.

## Integration recipes

### Shopify: auto-tag product images on upload

In your product-update webhook handler, call the API for each new image and write the `alt_text` back to the image's `alt` field on the Shopify product.

### WordPress: backfill alt-text for the Media Library

Walk every attachment without an alt, call the API for each URL, save `alt_text` to the `_wp_attachment_image_alt` post meta. Improves accessibility scores in one pass.

### SEO agency: image-search optimisation per client

For each client image, send `style=seo` with the client's target keywords (max 20). Output ranks better in Google Images than generic alt text.

### Multilingual publishing: one image, many languages

For each target language, call the API with a different `lang` value. The model writes natively in each language — no translation step needed.

### Bulk catalog re-processing

For sustained heavy traffic, honour HTTP 503 responses with `Retry-After` headers. Don't tight-retry; respect the indicated delay (typically 1 second). The cache will absorb most of the cost on subsequent runs.

## Best practices

1. **Pick the right style for the use case.** `descriptive` for accessibility audits and blog images; `seo` for image-search ranking; `ecom` for product pages. Mismatched style = output that misses the mark.
2. **Use language-specific calls, don't post-translate.** Pass `lang=es` for Spanish output. Quality is materially better than translating English output.
3. **Pre-validate URLs client-side when possible.** Confirm the URL is HTTPS, publicly accessible, and a JPEG/PNG/WEBP file before sending.
4. **For SEO mode, send 3–5 focused keywords.** 3–5 highly relevant keywords beat 20 broad ones. Stuffing degrades natural output quality.
5. **Handle 503 with backoff in bulk pipelines.** Respect the `Retry-After` header. Don't tight-retry.
6. **Cache is automatic; track but don't depend on it for billing.** The `cached` field is for cost-tracking visibility, not for differential pricing.
7. **For Shopify / Shopline / Wix integrations, do the call async.** Don't block the merchant's product-create flow on a 1.5-second API call. Background job (BullMQ, Sidekiq, Celery).

## FAQ

**Does cached content count against my monthly quota?**
Yes. Every API call counts, whether the response is freshly generated or served from cache. The cache benefits you by returning the same answer ~15× faster, not by saving on cost.

**Can I use this with private images (signed URLs, basic auth, cookies)?**
No. The API must be able to fetch the image with a plain HTTP GET — no auth headers, no cookies, no client certificates. Signed URLs with embedded credentials in the query string DO work as long as no extra headers are needed.

**What happens if the image is NSFW or otherwise flagged by AI safety filters?**
The API returns HTTP 422 with `"error": "content_blocked"`. Failed responses do not count against your billable quota.

**Can I customise the alt-text length?**
The model targets WCAG-recommended lengths (≤ 125 characters for `alt_text`, 1–3 sentences for `description`). Length is not currently configurable.

**Does the service train on my images?**
No. Images are streamed in memory, sent to Google's Gemini API for inference, and discarded. We do not retain image content.

**Is the API GDPR-compliant?**
The API is GDPR-aligned: we do not store consumer identity (api.market handles that), image URLs are logged in redacted form (query strings stripped), and generated text is cached by image content hash only — never by consumer. Full details: https://alttext.redditintel.dev/privacy

**What if my image URL redirects?**
The API follows up to 2 redirects. Relative redirects (common from WordPress and CMS sites behind CDNs) are supported — each redirect target is re-validated for safety.

**What about overage charges?**
On soft-limit plans, calls beyond your monthly quota are billed at the overage rate shown on your plan (typically $0.001–$0.005/call). On hard-limit plans, calls beyond quota are rejected with HTTP 403 and not billed. Failed requests (4xx/5xx) never count toward overages.

**What's the largest image you accept?**
10 MB. This covers any reasonable web image; product photos average 100–500 KB.

**How fresh is the model?**
We use Google Gemini 2.5 Flash (current as of mid-2026). The API surface is stable; we may upgrade the underlying model in the background without breaking your code. Output quality only improves over time.

## Pricing & limits

Pricing is set per plan — see the subscription tiers on this listing. All plans except Free are soft-limit: calls beyond your monthly quota are billed at the overage rate shown.

**Per-request limits:**

- Maximum image size: 10 MB
- Maximum URL length: 2048 characters
- Maximum `keywords` array length: 20 strings (each max 50 chars)
- URL HEAD timeout: 5 seconds
- URL GET timeout: 10 seconds
- Inference timeout: 15 seconds
- Maximum redirects followed: 2
- Concurrent in-flight requests (per backend): 50 (excess requests queue briefly or return 503)

**Free trial:** Subscribe to any tier to receive free trial calls per the plan terms.

## Built for production

Concrete operational guarantees:

- **HTTPS only** (TLS 1.3 via Let's Encrypt; HSTS-preloaded `.dev` domain)
- **No image content stored** — streamed in memory for processing, discarded after response
- **No PII storage** — we receive no consumer identity from api.market
- **Cached output retention: 30 days** — keyed by image content hash, not by consumer
- **Six-step request validation** before any AI call (schema → URL → SSRF → DNS → HEAD → streamed GET) — billing-on-200 only
- **OWASP API Security Top 10 aligned** — concrete control per risk, see [Security Statement](https://alttext.redditintel.dev/security)
- **Full privacy policy**: https://alttext.redditintel.dev/privacy

Subscribe to a plan, grab your api.market API key, and ship alt-text in production in under 5 minutes.

## Support

- **Privacy Policy:** https://alttext.redditintel.dev/privacy
- **Security Statement:** https://alttext.redditintel.dev/security
- **General support:** `support@redditintel.dev`
- **Security reports:** `security@redditintel.dev`

For billing, pricing, or platform issues: contact api.market support via your dashboard.


Generate WCAG-compliant alt text and SEO-ready image descriptions for any image URL in 130+ languages. One API call, two outputs. Free trial.

AI Alt Text API · WCAG Image Descriptions · 130+ Langs

Free

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