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Email Chekkr — Email verification. Check syntax, domains, MX and disposable emails. $2 per 1,000 emails.

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✨ What it does

Paste an address, upload a CSV of up to 10,000 rows, call the API, or ask your AI assistant. Every address gets a result and a score from 0 to 100.

Check What it looks for
✍️ Format One @, allowed characters, length limits, a real extension. International domains are supported.
🌍 Domain The domain exists.
📮 Mail server The domain has a mail server (MX record, or at least an address record) and hasn't opted out of email (null MX).
⏳ Temporary inbox Not one of 10,000+ known disposable services.
👥 Person or team Not a team inbox like info@, sales@ or support@.
🔤 Typos gmial.com → "did you mean gmail.com?", company.con → company.com.

🧭 How it works

flowchart TB
  W["🌐 Website<br/>checks run in the browser"]
  A["⚡ REST API<br/>for apps and scripts"]
  M["🤖 MCP<br/>for AI tools like Claude"]

  E["🧠 Shared checking engine<br/>format · typos · team address · temporary inbox<br/>🔎 mail server lookup (domain only)"]

  V["✅ Valid"]
  R["⚠️ Risky"]
  I["❌ Invalid"]
  U["❔ Unknown"]

  W --> E
  A --> E
  M --> E
  E --> V
  E --> R
  E --> I
  E --> U

  classDef web fill:#8b7cff,stroke:#5b4bdb,color:#ffffff,stroke-width:2px
  classDef api fill:#3ddc97,stroke:#1fb57f,color:#0d0f22,stroke-width:2px
  classDef mcp fill:#f2b544,stroke:#e39a2b,color:#0d0f22,stroke-width:2px
  classDef engine fill:#1c2048,stroke:#8b7cff,color:#ffffff,stroke-width:3px
  classDef valid fill:#1fb57f,stroke:#1fb57f,color:#ffffff
  classDef risky fill:#e39a2b,stroke:#e39a2b,color:#ffffff
  classDef invalid fill:#dc4a3d,stroke:#dc4a3d,color:#ffffff
  classDef unknown fill:#6b7090,stroke:#6b7090,color:#ffffff
  class W web
  class A api
  class M mcp
  class E engine
  class V valid
  class R risky
  class I invalid
  class U unknown
Loading
  • 🌐 Website: checks run in the visitor's browser. CSV files are never uploaded. Lookups go to Google Public DNS (Cloudflare as a fallback).
  • ⚡ API and 🤖 MCP: a small Node.js server on Render that runs the same engine and uses Node's built-in DNS. No third-party verification service.
  • 🔒 Privacy: only the domain (for example example.com) is ever looked up — never the full address. The API never stores or logs addresses.
  • 🧾 Safe downloads: results are added as new CSV columns (chekkr_status, chekkr_score, chekkr_reason, chekkr_suggestion). Cells starting with =, +, - or @ are escaped so spreadsheets don't run them as formulas.

Full details, with a diagram for every part, are in 🏗️ ARCHITECTURE.md.

🚦 Results

Result Meaning
🟢 Valid Well-formed, the domain has a mail server, no warning signs.
🟠 Risky Takes email, but something's off: temporary inbox, team address, likely typo, or no MX record.
🔴 Invalid Badly formed, or the domain doesn't exist or doesn't accept email.
⚪ Unknown The domain didn't answer in time. Check again later.

Note

Email Chekkr doesn't log in to mail servers, so "valid" means the address and its domain look deliverable, not that the exact mailbox was confirmed.

⚡ API in 10 seconds

curl "https://email-chekkr-api.onrender.com/v1/verify?email=sample.user@gmial.com"
Endpoint What it does
GET /v1/verify?email= · POST /v1/verify Check one address
POST /v1/verify/batch Check a list ({"emails": [...]})
GET /v1/domain?domain= Check a domain
POST /mcp MCP for AI tools (needs an API key)
GET /health Health check
Without a key With an API key 🔑
Requests per minute 30 per IP 120 per key
Emails per request 50 500
AI tools (MCP) — ✅

Send the key as Authorization: Bearer <key> (or X-API-Key). Full docs: API page.

📊 Capacity

Measured on the live API (free Render plan): 50 emails with 50 different domains in 0.47 s, about 100 emails a second. Repeated domains (like gmail.com) are near-instant because each domain is remembered for 10 minutes.

Per minute Per day Per month (30 days)
🔓 API, no key (per user) 1,500 2.16 million 64.8 million
🔑 API key — every domain new ~6,000 ~8.6 million ~259 million
🔑 API key — typical lists (up to the limit) 60,000 86.4 million 2.59 billion
🌐 Website (in the browser) ~3,000–6,000 (estimate) no limit no limit

Day and month figures assume non-stop use. The free server is shared by everyone and sleeps after 15 minutes idle (the first request then takes ~50 s). For heavy use, upgrade the Render instance.

🤖 MCP (AI tools)

Tools: verify_email, verify_emails_batch, check_domain.

  • Remote: https://email-chekkr-api.onrender.com/mcp with Authorization: Bearer <API key>.
  • Local: npm run mcp (stdio). Example config: examples/mcp-config.json.

☁️ Deploy the API

Render (free plan): Render → New → Blueprint → pick this repo. It uses render.yaml and the Dockerfile, and creates an API key for you (email-chekkr-api → Environment). Anything that runs Docker or Node 20+ works too (Railway, Fly.io, Google Cloud Run). All settings are environment variables — see .env.example.

🔐 Keys and secrets

  • API keys live only in the host's environment settings (on Render: email-chekkr-api → Environment → EMAIL_CHEKKR_API_KEYS). They are never stored in this repository.
  • .env files are ignored by git. .env.example lists the settings with no real values.
  • Every push and pull request runs npm run check:secrets, which fails if a key, token or personal email address is found.
  • All email addresses in the code, docs and tests are made-up samples.

🎨 Design

  • Colours: Night Blue #040A18, 66° White #FFFDF9, Shark Grey #B3C5D0 and 66° Blue #3952FF, with neutrals #F3F2F0 #ECECEC #E2E4E7 #DBDDE1. Green, amber and red appear only on results.
  • Fonts: Inter at weights 400 and 500 (no heavy bold), and IBM Plex Mono for small labels and code.
  • Logo: a 66° Blue sphere with a white tick inside a Night Blue rounded square (site/assets/img/logo.svg; flat version for the favicon).
  • Light and dark mode: follows the visitor's system setting, with a sun/moon toggle on every page. The choice is remembered in the browser.
  • Hero: a spinning globe with orbit rings and floating result chips, made in CSS only (no WebGL). It stops moving for visitors who prefer reduced motion.

🚀 Run it locally

Needs Node.js 20+ and Python 3 (for the website preview server). No npm install needed.

npm test                 # 45 tests: engine, API, MCP (no network needed)
npm run check:secrets    # scan for keys and personal emails
npm run serve            # website at http://localhost:8080
npm start                # API at http://localhost:8787
npm run mcp              # MCP server over stdio
npm run update:disposable  # refresh the disposable domain list

🌐 Publish the website

  1. Repo Settings → Pages → Source: GitHub Actions (one time — done).
  2. Merge to main. The Deploy site workflow publishes the site/ folder.
  3. Live at https://nexoradev-stack.github.io/Email-Chekkr/

📁 Project structure

site/                       the website (published to GitHub Pages)
├── index.html              home: single check, what we check, result guide, FAQ
├── bulk.html               bulk CSV check
├── pricing.html            plans and waitlist form
├── api.html                API and MCP docs
├── contact.html            contact form
├── privacy.html  terms.html  404.html
└── assets/
    ├── css/styles.css
    ├── js/app.js           page behaviour, theme toggle, forms
    ├── js/config.js        form settings (Web3Forms access key)
    ├── js/engine/          the checking engine (runs in browsers and Node)
    │   ├── syntax.js       format rules
    │   ├── typo.js         "did you mean …?" suggestions
    │   ├── dns.js          DNS-over-HTTPS lookups and MX logic
    │   ├── verify.js       combines the checks into a result and score
    │   ├── lists.js        team addresses, free providers, typo targets
    │   └── csv.js          CSV reading/writing
    ├── data/disposable-domains.txt
    ├── data/email-chekkr-sample.csv
    └── img/                logo.svg, favicon.svg, icon-512.png
server/                     the API and MCP server (Node built-ins only)
├── index.js                starts the HTTP server
├── app.js                  routes, API keys, CORS, limits
├── service.js              verify one, verify many, check domain
├── node-dns.js             DNS lookups with Node's dns module
├── mcp.js  stdio.js        MCP tools; MCP over stdin/stdout
└── rate-limit.js  config.js  runtime.js
docs/assets/banner.svg      README banner
examples/                   MCP config and API request examples
scripts/                    disposable list refresh, secrets check
test/                       engine, API and MCP tests
Dockerfile  render.yaml  .env.example
ARCHITECTURE.md             how it all works, with diagrams

🗺️ Roadmap

Phase What Status
1 🌐 Website: single and bulk checks in the browser ✅ Live
2 ⚡ REST API and 🤖 MCP server for AI tools ✅ Live
3 💳 Accounts, credits and payments (Razorpay), API keys in a database 🕒 Planned — pricing to be confirmed

🙌 Credits

Contributor Role
👤 nexoradev-stack Owner, product and design direction
🤖 Claude (Anthropic) Code, design and docs
🖱️ Cursor AI code editor

Disposable domain data: disposable-email-domains (CC0 1.0, public domain).

📄 Licence

© 2026 Email Chekkr. All rights reserved. The source is published for transparency; no licence to reuse it is granted.

About

Email Chekkr — Email verification. Check syntax, domains, MX and disposable emails. $2 per 1,000 emails.

Topics

automationemailemail-phishingemail-securityemail-verificationgithub-configjavascript

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