What is E.164 format?

E.164 is the ITU-T international numbering plan. An E.164 number starts with a + prefix, followed by a country calling code (one to three digits) and the subscriber number, for a maximum of 15 digits total. No spaces, dashes or brackets are included. Most telecom APIs require phone numbers in E.164 format.

Do I need to remove the leading zero from a UK phone number?

Yes. UK local numbers begin with a trunk prefix 0 (e.g. 07700 900000). In E.164 format, the trunk prefix is replaced by the country code +44, giving +447700900000. The same rule applies to German (+49), Dutch (+31) and French (+33) numbers.

What signals does the Telebase API return for a phone number lookup?

A single Telebase lookup returns the carrier name, country code, number type (mobile, landline, fixedVoip, nonFixedVoip, tollFree or voicemail), and active status, together with the SIM swap result, for $0.20 per check. SIM swap detection is launching soon for the UK, Germany, the Netherlands and France and is available via early access.

Developer tools

E.164 Phone Number Formatter and URL Encoder

Q: Why do I need to URL-encode a phone number for API calls?

The + character at the start of an E.164 number is a reserved character in URLs. In a query string, a raw + is interpreted as a space. To pass a phone number as a query parameter, encode the + as %2B. For example, +447700900000 becomes %2B447700900000.

Paste any phone number below to get the E.164 formatted version and the URL-encoded string you need for API query parameters. Runs entirely in your browser. No data leaves the page, no sign-up required.

Country

Phone number

E.164 Type a number above

URL-encoded For API query strings

Example curl

What is E.164?

E.164 is the ITU-T international numbering plan. It defines the format that every public telephone number worldwide must follow: a + prefix, a country calling code (one to three digits), and a subscriber number, with a maximum length of 15 digits and no spaces, dashes or brackets.

Most telecom APIs, including the Telebase carrier lookup API, require E.164 as the input format. If the number is not E.164 when it reaches the API, the lookup will fail or return incorrect results.

Why URL encoding matters for API calls

The + character at the start of an E.164 number is a reserved character in URLs. In a query string, a raw + is interpreted as a space. To pass a phone number as a query parameter, you need to encode the + as %2B.

For example, +447700900000 becomes %2B447700900000 in a URL. The formatter above gives you both versions so you can copy the right one for your context.

How the formatter works

Step one: select the country

Choose the country calling code from the dropdown. The four markets Telebase covers for KYC phone validation (GB, DE, NL, FR) are listed first.

Step two: enter the number

Paste or type the subscriber number. The tool strips spaces, dashes, brackets and leading zeroes automatically. If the number already has a + and country code, the tool detects that and skips the prefix.

Step three: copy the output

The E.164 string and the URL-encoded version appear instantly. Use the copy buttons, or grab the example curl command to test against any phone lookup API.

Common formatting mistakes

Leading zero not removed. UK numbers are often written as 07700 900000. The leading zero is a trunk prefix, not part of the international number. E.164 for this number is +447700900000, not +4407700900000.
Raw + in a query string. Passing ?phone=+447700900000 sends a space instead of a plus. Use ?phone=%2B447700900000.
Spaces and punctuation left in. E.164 contains only digits and the leading +. Any spaces, dashes, dots or brackets must be stripped before the API call.
Country code applied twice. If someone pastes +447700900000 while GB is selected, a naive formatter would produce +44447700900000. This tool checks for an existing prefix first.

E.164 formatting rules by market

Each of the four markets Telebase covers has its own trunk prefix convention. The table below shows the local format, what to strip, and the resulting E.164 number.

Quick reference

United Kingdom (+44): local numbers start with 0 (e.g. 07700 900000). Strip the leading 0. E.164: +447700900000.
Germany (+49): local numbers start with 0 (e.g. 0151 12345678). Strip the leading 0. E.164: +4915112345678.
Netherlands (+31): local numbers start with 0 (e.g. 06 12345678). Strip the leading 0. E.164: +31612345678.
France (+33): local numbers start with 0 (e.g. 06 12 34 56 78). Strip the leading 0. E.164: +33612345678.

Using the formatted number with an API

Once you have the URL-encoded number, you can pass it directly to any phone lookup endpoint. The Telebase quickstart walks through a complete first lookup. The API returns carrier, country, number type and active status in a single call with the SIM swap check, at $0.20 per check.

Example: Telebase lookup with a formatted number

# Format the number to E.164, URL-encode the +
curl -s 'https://api.telebase.io/lookup?phone=%2B447700900000' \
  -H 'Authorization: Bearer tb_live_xxxxxxxxxxxxxxxxxxxxxxxx'

# Response
{
  "phoneNumber": "+447700900000",
  "active": true,
  "carrier": "EE",
  "country": "GB",
  "numberType": "mobile",
  "simSwap": "UNKNOWN",
  "simSwapAt": null,
  "_meta": { "activeSource": "LINE_STATUS" }
}

simSwap returns UNKNOWN for GB, DE, NL and FR numbers while carrier registration completes. SIM swap detection is launching soon: join early access.

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