# SVCB

`SVCB` adds a [Service Binding record](https://www.rfc-editor.org/rfc/rfc9460) to a domain. The name should be the relative label for the record. Use `@` for the domain apex.

The priority must be a positive number, the address should be an ip address, either a string, or a numeric value obtained via [IP](/language-reference/top-level-functions/ip.md).

The params may be configured to specify the `alpn`, `ipv4hint`, `ipv6hint`, `ech` or `port` setting. Several params may be joined by a space. Not existing params may be specified as an empty string `""`

Modifiers can be any number of [record modifiers](https://docs.dnscontrol.org/language-reference/record-modifiers) or JSON objects, which will be merged into the record's metadata.

{% code title="dnsconfig.js" %}

```javascript
D("example.com", REG_MY_PROVIDER, DnsProvider(DSP_MY_PROVIDER),
  SVCB("@", 1, ".", "ipv4hint=123.123.123.123 alpn=h3,h2 port=443"),
);
```

{% endcode %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.dnscontrol.org/language-reference/domain-modifiers/svcb.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.