---
title: Check SSL/TLS Certificate
description: Verify a domain's TLS certificate from the cellular network, including expiry.
lastUpdated: "2026-09-23"
---

> **For AI agents:** the complete documentation index is at [llms.txt](/llms.txt). Append `.md` to any page URL for its markdown version.

Fetch and inspect the TLS certificate a domain serves, as seen from the mobile network: issuer, subject, validity dates, time before expiry. Catch an expiring certificate before your users do, and detect interception (a certificate that differs on the cellular path).

## Parameters

| Parameter | Required | Description |
| ----------- | ---------- | ------------- |
| Domain name | Yes | The domain whose certificate to check. |

Plus the shared [connection settings](/tests/actions/cellular/overview#connection-settings).

## Results and metrics

In the action report (`result`), for the certificate chain:

| Field | Description |
|-------|-------------|
| `expire_in_seconds` | Time remaining before expiry. The field to alert on. |
| `not_before`, `not_after` | Validity window. |
| `issuer`, `subject` | Who issued the certificate and for whom (common name, organization, country...). |
| `signature_algorithm`, `public_key_algorithm` | Cryptographic algorithms in use. |
| `fingerprint_sha_256`, `fingerprint_sha_1`, `serial_number` | Certificate identity, to detect substitution. |
| `dns_names` | The domains the certificate covers. |
| `certificate_error` | Any validation error encountered. |

In Analytics, each run feeds the certificate measurement with `expire_in_seconds`, the issuer and subject details, fingerprints, and `duration_seconds`, tagged by status, domain name, certificate error, and algorithms. Alert on `expire_in_seconds` to get ahead of renewals.

## What's next?

<Columns cols={2}>
  <Card title="API Call" icon="cloud" href="/tests/actions/cellular/api-call">

    Verify the service behind the certificate

</Card>
  <Card title="Alerts" icon="bell" href="/alerting/alerts">

    Trigger an alert before the certificate expires

</Card>
</Columns>