# how.is TLS Certificate Inspector

> how.is TLS Certificate Inspector is a paid API for AI agents from how.is, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-31).

Returns TLS certificate validity, issuer, protocol, cipher, and days until expiry for a given domain.

## Facts

- Endpoint: POST https://how.is/v1/domain/tls?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/how-is-tls-certificate-inspector-e0c3939a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_levV-j62Piif0A_-lUfHn

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability how-is-tls-certificate-inspector-e0c3939a -d '<json body>'
```

Example prompt: Can you check the TLS certificate for api.stripe.com — I want to know who issued it, whether it's valid, what protocol it's using, and how many days until it expires?

## When to prefer this

Use this endpoint when you need programmatic, structured TLS certificate data for a domain — especially issuer identity, protocol version, cipher, and expiry countdown — rather than a raw openssl command or manual browser check. Ideal for security audits, pre-integration checks, automated monitoring pipelines, and agent workflows that need to reason about certificate trustworthiness before making outbound connections.

## Known failure modes

- Domain does not exist or is unreachable — certificate lookup fails
- Domain has no HTTPS listener — no TLS data returned
- Invalid domain format supplied — input validation error
- Certificate is expired or revoked — returned with validity flag reflecting state
- Network timeout reaching the target domain
- Rate limiting or payment failure via x402 protocol

## How this service works

Certificate validity, issuer, protocol and days until expiry for a domain.

## Output

A JSON object containing: validity status, issuer, subject, subject alt names, validFrom and validTo dates, daysUntilExpiry (integer), TLS protocol version, cipher suite, and whether the certificate is self-signed. Also includes a payment receipt with rail, tool, USD charge, and settlement transaction hash.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "domain": {
   "type": "string",
   "maxLength": 253,
   "description": "A bare domain name, e.g. example.com"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "data": {
   "_shape": "data.data: valid, issuer, subject, subjectAltNames, validFrom, validTo, daysUntilExpiry, protocol, cipher, selfSigned."
  },
  "result": "TLS certificate for the requested subject",
  "receipt": {
   "rail": "x402",
   "tool": "tls",
   "charge_usd": 0.005,
   "settlement_tx": "0x…"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/how-is-tls-certificate-inspector-e0c3939a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from how.is](https://www.zero.xyz/host/how.is/llms.txt)