Email verification and phone validation API

Authentication

Create a key on the API keys page and send it in the Authorization header. Keys start with sv_live_ and are shown once. Keep them on your server.

Authorization: Bearer sv_live_...

Verify an email address

GET or POST https://simpleverifier.com/api/v1/verify with email. Syntax, domain, disposable and live mailbox (SMTP) checks run in one call.

curl "https://simpleverifier.com/api/v1/[email protected]" \
  -H "Authorization: Bearer $SIMPLEVERIFIER_KEY"

{
  "email": "[email protected]",
  "status": "valid",
  "reason": "Mailbox exists",
  "send_advice": "safe",
  "reason_detail": "The mail server confirmed this mailbox exists.",
  "catch_all_confidence": null,
  "catch_all_reasons": [],
  "catch_all_signals": [],
  "smtp_available": true,
  "mailbox_probed": true,
  "mailbox_checked": true,
  "action": "send",
  "risk": "low",
  "likely_invented": false,
  "reason_code": "mailbox_exists",
  "score": 100,
  "score_basis": "confirmed"
}

send_advice and reason_detail match the columns of a list download. send_advice is one of safe (mailbox confirmed), care (the domain takes mail but the mailbox could not be confirmed), retry (the server did not answer our check; try later) or do_not_send (it will bounce).

catch_all_confidence, catch_all_reasons and catch_all_signals are new and optional to read. They are set only when reason is Accepts all addresses: the label is higher, medium or lower likelihood that the mailbox is real, and the reasons are plain sentences, and the signals are stable codes (matches_confirmed_format, matches_confirmed_single_word, matches_list_format, differs_from_confirmed_format, name_guess_variants, placeholder_address, disposable_domain, department_inbox, random_looking, free_provider). Every other reply has null, [] and []. The row stays risky with send_advice care; the label is a ranking, not a percentage, and it opens no extra mail connection. How it is built and measured. List downloads carry the same three columns (reasons joined into one cell, signals joined with ;). filter=safe_likely returns safe rows plus higher-likelihood catch-alls, and filter=safe_not_lower returns safe rows plus every catch-all not ranked lower.

{
  "email": "[email protected]",
  "status": "risky",
  "reason": "Accepts all addresses",
  "send_advice": "care",
  "catch_all_confidence": "higher",
  "catch_all_reasons": [
    "Looks like a person's name (first.last).",
    "Same first.last format as 2 confirmed addresses on this domain in earlier checks.",
    "Still unconfirmed: the server accepts every address. Send in small batches and watch bounces."
  ],
  "catch_all_signals": ["matches_confirmed_format"]
}

• smtp_available: live mailbox (SMTP) checking was available on our side for this call. It says nothing about this particular address.
• mailbox_probed: this address’s mail server was asked about it, now or in a recent cached answer. It is false for answers that need no probe: bad format, disposable, role address, no mail server, or a provider that never confirms mailboxes.
• mailbox_checked: the original name for smtp_available, with the same value. It stays in every reply so existing integrations keep working; read mailbox_probed to know whether this address was checked.

Decision fields for agents and automations

Every answered check from /api/v1/verify and every row from the MCP tools also carries four fields with a fixed shape and no null, so an AI agent, Zapier step or script can branch without parsing sentences. They are added next to the fields above; nothing existing changed. They are worked out from status and reason and are never more hopeful than status.

• action: send, send_with_care, retry_later or do_not_send (the machine form of send_advice). Only status valid ever gives send, and invalid always gives do_not_send.
• risk: low only for a confirmed mailbox, high for do_not_send or any unconfirmed address that looks invented, medium otherwise.
• likely_invented: true when the address looks made up by an LLM or a guesser. It is never true for a confirmed mailbox, and otherwise only for a placeholder local part (test@, demo@, user@, john.doe@, firstname.lastname@; trailing digits ignored), a reserved or template domain (example.com, .test, yourdomain.com), a domain with no mail server at all (not a typo of a real one), or a sequential or repeated local part (1234@, abcd@, aaaa@). Role inboxes and real-looking names are never flagged by it.
• reason_code: a stable code for reason (table below). Reason sentences may be reworded; codes do not change. New codes may be added: treat an unknown code like other and go by action. unknown means the result had no status.

{
  "email": "[email protected]",
  "status": "invalid",
  "reason": "No mail server",
  "send_advice": "do_not_send",
  "action": "do_not_send",
  "risk": "high",
  "likely_invented": true,
  "reason_code": "no_mx"
}

Validate a phone number

GET or POST https://simpleverifier.com/api/v1/phone with phone and an optional country (two letters, default US) used for numbers written without +. With the phone add-on (or the older Email + Phone plan), valid numbers also get a live carrier lookup (5,000 a month; failed lookups don't count). Pass live=false to skip it.

curl "https://simpleverifier.com/api/v1/phone?phone=07911%20123456&country=GB" \
  -H "Authorization: Bearer $SIMPLEVERIFIER_KEY"

{
  "input": "07911 123456",
  "phone_status": "valid",
  "phone_e164": "+447911123456",
  "phone_country": "GG",
  "phone_type": "mobile",
  "phone_carrier": "JT Group Limited",
  "phone_line_type": "mobile",
  "live_lookup": true
}

phone_type comes from the numbering plan and is free on every plan. phone_carrier and phone_line_type appear only when live_lookup is true.

Examples

Prefer a client library? The Node.js and Python SDKs add typed errors, automatic retries on rate limits and a bulk helper. To give Claude, Cursor or another AI agent these checks as tools, connect the SimpleVerifier MCP server with the same key.

Node.js

const res = await fetch(
  "https://simpleverifier.com/api/v1/verify?email=" + encodeURIComponent(email),
  { headers: { Authorization: `Bearer ${process.env.SIMPLEVERIFIER_KEY}` } }
);
const { status, reason } = await res.json();
if (status === "invalid") throw new Error(`Please check your email: ${reason}`);

Python

import os, requests

r = requests.get(
    "https://simpleverifier.com/api/v1/verify",
    params={"email": email},
    headers={"Authorization": f"Bearer {os.environ['SIMPLEVERIFIER_KEY']}"},
    timeout=30,
)
result = r.json()  # {"status": "valid" | "risky" | "invalid", "reason": ...}

Block fake and disposable signups

Call this endpoint where an account is created, block action do_not_send, warn on role and catch-all addresses, and let timeouts through. Signup protection recipes for a Supabase Auth hook, a Clerk webhook, a Firebase blocking function, Next.js, Express, Cloudflare Workers, Zapier, n8n and Webflow or Framer forms.

Guides by language and framework

Complete, copy-ready integrations with a syntax check first, timeouts, and handling for valid, risky and invalid results.

• Email verification API in PHP
• Validate email addresses in Laravel with a mailbox check
• Verify email addresses on WordPress forms
• Verify an email address in Python
• Validate email addresses in Django
• Validate email addresses in Flask
• Email verification API in Node.js
• Verify email addresses in Next.js
• Validate email addresses in Express with middleware
• Verify an email address in Ruby
• Validate email addresses in Rails
• Email verification API in Go
• Email verification API in Java
• Validate email addresses in Spring Boot
• Email verification API in C# and .NET
• Validate email addresses in a React form

Google Sheets and other integrations

To verify a column of emails without writing code, paste the SimpleVerifier Google Sheets script into your sheet. It calls this API with your key, adds a Verify selected emails menu that writes Status and Reason beside your list, and adds =SV_VERIFY() and =SV_PHONE_FORMAT() formulas. No Marketplace install. Instantly, Smartlead, the SDKs and the MCP server are listed on the integrations page.

Errors and limits

Errors return JSON with an error message. A mailbox check can take a few seconds when a mail server is slow, so set a client timeout of about 30 seconds.

Monthly calls by plan

Each request to /api/v1/verify, /api/v1/phone or an MCP tool call is one call. /api/v1/me and MCP handshakes are free. Months are counted in UTC. Every key allows 120 calls a minute.

Common questions

How much does the SimpleVerifier API cost?

API access comes with Pro ($39/month, 10,000 calls a month included, then $1.50 per 1,000), Business ($99, 100,000 included, then $1.00 per 1,000) and Agency ($249, 300,000 included, then $1.00 per 1,000). The Starter CSV plan does not include it. Calls past the included ones are added to the next monthly invoice; on yearly billing the included calls are the monthly limit and further calls return 402 until the 1st (UTC). The $20/mo phone add-on adds 5,000 live carrier lookups a month. Pro subscriptions started before 23 October 2026 keep API access with no monthly quota.

Is there a rate limit?

Each key can make 120 calls a minute, counted over a sliding 60-second window. Past that the API answers 429 with a Retry-After header giving the whole seconds until the key can call again (the same number is in the JSON body as retry_after_seconds); wait that long, then retry. For lists of thousands of addresses, upload a CSV in the dashboard instead: it runs the same checks in bulk and returns valid, risky and invalid files.

Can I call the API from the browser?

No. Keep keys on your server. Anyone who can read a key from your page can use your plan. Call the API from your backend and pass the result to your form.

Does the phone endpoint tell me if a number is in service?

No. It confirms the number fits its country's numbering plan, normalises it to E.164 and, with the phone add-on, returns the carrier and real line type (mobile, landline or VoIP). No lookup can confirm someone is using a number today.