Authentication
Send an API key as a bearer token. This endpoint does not state a specific permission in the specification, so give your key the least it needs and check the response rather than assuming.
This endpoint takes no organisation id. Your key already identifies the organisation it belongs to, and the response is scoped to it.
Try it
Replace anything in angle brackets with your own values, and the key placeholder with a key from your dashboard.
curl -X GET https://api.zinndigital.com/v1/sites/{siteId}/vitals \
-H "Authorization: Bearer zdk_live_…"Signed in? The API console in your dashboard fills in your real organisation id and your own key, and runs the request against the live API so you can see the actual response. Open this endpoint in the API console
Details
The site's newest Core Web Vitals reading — LCP, CLS and INP for its **homepage**, with the "good / needs improvement / poor" band for each and for the reading as a whole. Backs the Performance tab's vitals card and the free SEO Basics tile, both of which are sold as included on every plan and every site. RLS-scoped to a site the caller can view (`sites.view`); an out-of-scope or unknown id is a `404`, exactly like `getSite`. **Homepage only, by design.** Every surface that sells this sells *homepage* Core Web Vitals. Measuring every URL of every site is a different product. **Collection is asynchronous.** Readings are taken off the request path by a scheduled collector and read back here — a live Lighthouse run would be a 20-second uncached external call on a tab that mounts for every site (CLAUDE.md §2.16). Until a site has been measured, `available` is `false`, every metric is `null` and every band is `unknown`. **`source` must be rendered.** A `lab` reading is a synthetic Lighthouse run; a `field` reading is what real Chrome users experienced (Chrome UX Report) and is what Google ranks on. Field data does not exist for sites below CrUX's traffic threshold — which is most low-traffic sites — so `lab` is the coverage tier. Presenting a lab score as though real users produced it is a false claim about what visitors experienced, so clients must label which one they are showing.
Parameters
| Name | Type | Required | What it is |
|---|---|---|---|
siteId (path) | Uuid | Yes | Site ID (UUIDv7). |
Response
| Name | Type | Required | What it is |
|---|---|---|---|
available | boolean | Yes | Whether any vitals reading exists for this site yet. |
url | string | Yes | The exact URL measured. Empty when unavailable. |
source | string<field, lab, > | Yes | `field` = Chrome UX Report (real users, what Google ranks on); `lab` = a synthetic Lighthouse run. Clients MUST label which is shown. Empty string when unavailable, following `p… |
field_available | boolean | Yes | Whether real-user (field) data exists for this site at all, independent of which reading is returned — so the UI can say "no real-user data yet" while still showing the lab number. |
lcp_ms | object | Yes | Largest Contentful Paint, p75, milliseconds. Good ≤ 2500, poor > 4000. |
cls_milli | object | Yes | Cumulative Layout Shift, p75, in **thousandths** (0.083 → `83`). An integer so no band comparison is ever made against a float at the 0.1/0.25 boundaries; clients render `cls_mi… |
inp_ms | object | Yes | Interaction to Next Paint, p75, milliseconds. Good ≤ 200, poor > 500. INP replaced First Input Delay as a Core Web Vital in March 2024; FID is retired and is deliberately not re… |
ttfb_ms | object | Yes | Time to First Byte — a diagnostic, not a Core Web Vital. |
fcp_ms | object | Yes | First Contentful Paint — a diagnostic, not a Core Web Vital. |
performance_score | object | Yes | Lighthouse performance score, 0–100. Always `null` on a `field` reading — the Chrome UX Report computes no score, and inventing one would present a number Google never produced. |
accessibility_score | object | Yes | Lighthouse accessibility score, 0–100 (docs/85 §2.1). Lighthouse computes all four of its categories from a **single** page load, so this costs about a second on a 10–30 s run —… |
best_practices_score | object | Yes | Lighthouse best-practices score, 0–100 — mixed content, deprecated APIs, console errors. `null` on a `field` reading. |
seo_score | object | Yes | Lighthouse SEO score, 0–100. `null` on a `field` reading. |
stack_packs | string[] | Yes | The technology stacks Lighthouse detected on this run (`wordpress`, `woocommerce`, …). **Ids only.** Lighthouse also ships stack-specific remediation *text*; that is untranslate… |
band | VitalsBand | Yes | A Core Web Vitals verdict against Google's published p75 thresholds. The overall `band` is the **worst** of the three measured metrics, because that is how Google assesses a pag… |
lcp_band | VitalsBand | Yes | A Core Web Vitals verdict against Google's published p75 thresholds. The overall `band` is the **worst** of the three measured metrics, because that is how Google assesses a pag… |
cls_band | VitalsBand | Yes | A Core Web Vitals verdict against Google's published p75 thresholds. The overall `band` is the **worst** of the three measured metrics, because that is how Google assesses a pag… |
inp_band | VitalsBand | Yes | A Core Web Vitals verdict against Google's published p75 thresholds. The overall `band` is the **worst** of the three measured metrics, because that is how Google assesses a pag… |
measured_at | object | Yes | — |
opportunities | SiteVitalsOpportunity[] | Yes | What is actually making this page slow, **largest saving first** — the "why" behind the numbers above. ⚠️ An empty array does **not** mean "nothing to fix". It means this readin… |
screenshots | SiteVitalsScreenshots | Yes | What the page looked like while it loaded — the filmstrip and the finished render. `available` is reported separately from the parent envelope's flag because a perfectly good me… |
Errors this endpoint can return
401 · 403 · 404 · 429