A tel: URI is the standard way, defined in RFC 3966, to represent a telephone number as a clickable link. Putting it in an anchor's href lets a browser or phone launch the dialler with the number pre-filled.

What is the difference between a global and a local number?

A global number is in full international form and starts with a plus sign, like tel:+14155550101. A local number has no country prefix and must carry a phone-context parameter naming the dialling domain or a global prefix so it can be resolved unambiguously.

What characters are allowed in a tel: URI?

The visual-separator characters hyphen, dot and parentheses are permitted between digits but are usually stripped. Only digits, a leading plus for global numbers, and the defined parameters (ext, isub, phone-context) are kept. Other characters are percent-encoded.

How do I add an extension?

Append an ext parameter, for example tel:+14155550101;ext=42. The extension is dialled after the main number connects. This tool adds it for you when you fill the extension field.

Is my number uploaded?

No. The URI is built entirely in your browser, so the phone number is never sent to a server.

Tel URI Encoder — Gera Tools

The tel: URI encoder turns an ordinary phone number into a valid RFC 3966 tel: URI — the format you put in an href to make a clickable call link or encode in a QR code. It handles international (global) and local numbers, optional extensions, and percent-encodes anything that needs it.

How it works

RFC 3966 distinguishes two number forms. A global number is fully international and begins with + followed by digits, e.g. tel:+14155550101. A local number has no country code and therefore must include a phone-context parameter — either a global number prefix (+1) or a domain (example.com) — so the dialler knows how to interpret it: tel:7042;phone-context=example.com.

The encoder strips visual separators (spaces, -, ., (, )) from the digits since RFC 3966 treats them as cosmetic. It then assembles the scheme, the number, and any parameters as ;name=value pairs. An extension is added as ;ext=NN. Parameter values containing reserved characters are percent-encoded.

Example

Input:  (415) 555-0101  (global)
Output: tel:+14155550101

Input:  7042  (local), context example.com, ext 5
Output: tel:7042;ext=5;phone-context=example.com

Notes

Use a global + number whenever you can — it works regardless of where the caller is. Reserve local numbers with phone-context for intranet or extension-style dialling. The resulting URI drops straight into <a href="tel:...">. Everything runs locally; your number is never uploaded.