Preview a segment

How many contacts a set of rules currently matches, and a sample of them, without saving the segment. Call this before sending to one.

Rules take one of four kinds of field:

Kind	Fields	Example
Contact columns	email, name, status	{"field": "email", "op": "ends_with", "value": "@acme.com"}
Custom fields	any key from GET /contact-fields	{"field": "plan", "op": "equals", "value": "pro"}
Engagement	opened, clicked, emailed	{"field": "opened", "op": "within_days", "value": "90"}
Membership	tag, interest	{"field": "tag", "op": "equals", "value": "vip"}

tag matches by NAME, interest matches by ID. That asymmetry is deliberate. A tag is written by name everywhere — created on first use, case-insensitively — so a rule holding a ULID would break the moment somebody renamed it. An interest is an answer to a question the contact was asked and its name is form copy, so rewording "Product updates" must not silently empty every segment built on it.

Membership fields take equals, not_equals, is_set (has any) and is_not_set (has none). Deliberately not contains: a tag is on a contact or it is not, and a substring match over a set would let contains "vip" quietly also match vip-churn-risk.

not_equals means "does not carry it", not "carries something else". A contact with both vip and churn-risk is EXCLUDED by tag is not vip — they carry it. A contact with no tags at all is included, because they do not.

A rule we cannot evaluate — an unparseable number or date, a blank tag — matches nothing. Widening is the dangerous direction: it mails people who were never meant to be in the audience, and it does so quietly.

curl -X POST 'https://app.mailyte.com/api/v1/segments/preview' \
  -H 'Authorization: Bearer mk_live_YOUR_API_KEY'

const response = await fetch('https://app.mailyte.com/api/v1/segments/preview', {
  method: 'POST',
  headers: {
    Authorization: 'Bearer mk_live_YOUR_API_KEY',
  },
});
const { data } = await response.json();

import requests
response = requests.post(
    "https://app.mailyte.com/api/v1/segments/preview",
    headers={"Authorization": "Bearer mk_live_YOUR_API_KEY"},
)
data = response.json()["data"]

<?php

$response = Http::withToken('mk_live_YOUR_API_KEY')
    ->post('https://app.mailyte.com/api/v1/segments/preview');

$data = $response->json('data');

require "net/http"
require "json"
uri = URI("https://app.mailyte.com/api/v1/segments/preview")
request = Net::HTTP::Post.new(uri)
request["Authorization"] = "Bearer mk_live_YOUR_API_KEY"
response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |http| http.request(request) }