Soni API is a public developer utility API platform operated by Soniverse GmbH in Germany. Version 1 offers a free online link checker API, on-page SEO checker, and GEO (generative engine optimization) checker with API-key authentication and interactive OpenAPI docs.

How do I authenticate?

Open /register to create an account and receive an API key, then send Authorization: Bearer on protected endpoints such as /api/v1/link-checks, /api/v1/seo-checks, and /api/v1/geo-checks.

What is the difference between the SEO and GEO checkers?

The SEO checker audits classic on-page signals (title, meta description, headings, HTTPS, Open Graph). The GEO checker focuses on Generative Engine Optimization: JSON-LD/FAQPage, /llms.txt, robots signals for AI crawlers, and citeable page structure. Both return a score, findings, and improvements. Neither predicts rankings or citations.

Does the link checker execute JavaScript?

Not in v1. Metadata and audits use static HTML from an SSRF-aware HTTP fetch. Optional JavaScript-rendered checks are planned for a later version.

Where is Soni API operated from?

Soni API is operated by Soniverse GmbH in Pinzberg, Germany. Product documentation is in English; imprint and privacy pages cover the German operator.

Yes. The public /stats page shows aggregate request volume, success rate, and latency. It does not expose personal data or checked URLs.

Yes. v1 offers a free tier with a configurable per-API-key hourly rate limit. The service is provided as is, without warranty of availability or accuracy.

Soniverse · Germany · Free to start

Soni API

Q: What is an online link checker API?

An online link checker API fetches a URL over HTTP and returns whether it resolves, which redirects occurred, the final status code, and often safe page metadata — so applications can validate links programmatically. Soni API exposes this as POST /api/v1/link-checks.

Free online link checker API, plus on-page SEO and GEO (generative-engine readiness) checkers. Interactive OpenAPI docs. No credit card. No fake guarantees.

Open interactive docs Get a free API key Contact

POST /api/v1/link-checks · live shape

// Authorization: Bearer soni_…
{
  "originalUrl": "https://amazon.de/",
  "finalUrl": "https://www.amazon.de/",
  "finalStatusCode": 200,
  "redirectChain": [
    { "url": "https://amazon.de/", "statusCode": 301 },
    { "url": "https://www.amazon.de/", "statusCode": 200 }
  ],
  "metadata": {
    "title": "Amazon.de: …",
    "description": "Entdecken, shoppen…",
    "canonical": "https://www.amazon.de/"
  }
}

What Soni API is

Citeable product facts for developers, search engines, and generative engines.

Operator

Soniverse GmbH (Pinzberg, Germany) runs Soni API. Product UI and docs are in English; legal pages cover the German operator.

What you call

POST /api/v1/link-checks, POST /api/v1/seo-checks, and POST /api/v1/geo-checks with Authorization: Bearer <api_key>.

What we do not claim

No uptime, ranking, or citation guarantees. Results are best-effort heuristics on static HTML. See the disclaimer and llms.txt.

From zero to first call

Three steps. Register for a key, authorize in the docs, then try an endpoint.

01

Register

Open the registration page. You are signed in afterwards and can view or manage keys on your account page.
02

Authorize

Open API docs while logged in — your default key is applied automatically. Guests paste a key via Authorize (Authorization: Bearer …).
03

Call

Hit a v1 endpoint with a URL and inspect the live JSON — link status, SEO score, or GEO findings.

APIs

Three utilities in v1: link intelligence, on-page SEO audit, and GEO readiness for AI search.

Browse all endpoints

Link Checker

Follow redirects with a hard cap. Return final status, redirect chain, and safe page metadata — without storing full HTML bodies. Dedicated overview: online link checker API.

POST /api/v1/link-checks 60/hour SSRF-aware

Try in API docs → Learn more

Request cURL

POST /api/v1/link-checks
Authorization: Bearer soni_…
Content-Type: application/json

{
  "url": "https://example.com/page"
}

SEO Checker

Fetch a URL and return an on-page SEO score, rating, structured findings, and improvement suggestions — title, meta, headings, HTTPS, Open Graph, and more. Heuristic only; not a ranking prediction. Overview: SEO checker API.

POST /api/v1/seo-checks 60/hour SSRF-aware

Try in API docs → Learn more

Response shape

{
  "score": 84,
  "maxScore": 100,
  "rating": "good",
  "findings": [ { "id": "canonical_missing", … } ],
  "improvements": [ "Add canonical…" ]
}

GEO Checker

Generative Engine Optimization audit: JSON-LD / FAQPage, /llms.txt, robots signals for AI crawlers, citeable titles, and concrete improvements. Heuristic only — not a citation guarantee. Overview: GEO checker API.

POST /api/v1/geo-checks 60/hour SSRF-aware

Try in API docs → Learn more

Response shape

{
  "score": 91,
  "maxScore": 100,
  "rating": "excellent",
  "metrics": { "hasFaqPageSchema": true, "llmsTxtReachable": true },
  "improvements": []
}

Roadmap

Not in v1 — planned so we can extend without a rewrite. Static link checks stay the default.

Content suitability

Is the page still useful?

Beyond HTTP 200: detect soft-404s, parked domains, removal placeholders, and mismatches against optional expected-content hints — without storing full HTML.
JS-rendered checks

Headless browser workers

Opt-in async jobs (Playwright/Chromium) for pages that only expose metadata after client-side rendering. Same SSRF limits; separate quotas.
JS page render

Full HTML after JavaScript

Send a URL, get the complete DOM as HTML after the page runs client-side JavaScript — for SPA shells and dynamically injected content.

Later: paid plans, API key rotation UI, account dashboard.

FAQ

Straight answers for developers and generative engines alike.

What is an online link checker API?

A service you call over HTTP to validate URLs: redirects, final status code, and safe metadata — without opening a browser. Soni API exposes this as POST /api/v1/link-checks. Overview: online link checker API.

What is Soni API?

A public utility API platform by Soniverse GmbH (Germany). v1 ships an online link checker, on-page SEO, and GEO audits with API-key auth and interactive OpenAPI docs.

How do I get an API key?

Open the registration page. After signup you land on your account with the key ready to copy (and recoverable anytime after login). Signed-in visitors get the default key applied automatically in the API docs.

What is the difference between SEO and GEO checkers?

SEO covers classic on-page signals (title, meta, headings, HTTPS, Open Graph). GEO focuses on generative-engine readiness: JSON-LD/FAQPage, /llms.txt, AI crawler robots signals, and citeable structure. Neither predicts rankings or citations.

Does link checking run JavaScript?

Not in v1 — we parse static HTML only. JS-rendered checks are planned for a later version.

Where is the operator based?

Germany (Pinzberg). See the imprint and privacy pages.

Is Soni API free?

Yes — free tier with a configurable hourly rate limit per API key. Provided as is, without warranty.

Can I see API usage?

Yes — /stats shows public aggregates (volume, success rate, latency). No personal data or checked URLs.

Honest by design

Default rate limit: 60 requests per API key per hour. Provided as is — public targets can be slow, hostile, or misleading. See the disclaimer.

Soni API

What Soni API is

Operator

What you call

What we do not claim

From zero to first call

Register

Authorize

Call

APIs

Link Checker

SEO Checker

GEO Checker

Roadmap

Is the page still useful?

Headless browser workers

Full HTML after JavaScript

FAQ

Honest by design