Systems Lab

Agent skill

cold-email-verifier

Use when the user wants to verify cold emails, enrich a lead list, or autonomously guess email addresses from a CSV using ValidEmail.co or the open-source Reacher engine.

activeNeeds a keyActs undeclared410 words

Filed under Outbound email.

From Varnan-Tech/opendirectory · 57 skills · 626 · pushed 2026-08-16

What it does when it runs

Use when the user wants to verify cold emails, enrich a lead list, or autonomously guess email addresses from a CSV using ValidEmail.co or the open-source Reacher engine.

Read from the skill and the 4 files bundled beside it. A skill’s own description is written to be selected by an agent, so it describes the job and not the dependencies.

Keys and connectors you must supply
  • VALIDEMAIL_API_KEY
Hosts it reaches
  • autocomplete.clearbit.com
  • download-directory.github.io
  • manus.im
  • opendirectory.dev
  • validemail.co
Tool permissions it declares
No allowed-tools in the frontmatter. It does act, so it runs under whatever permissions your session already grants.
Actions present in the files
shellnetwork

Ask about cold-email-verifier

Opens your assistant with this page's verified links already in the prompt.

Is this safe to install?ClaudeChatGPT
Adapt it to my stackClaudeChatGPT
What else do I need for it to workClaudeChatGPT
Rather ask a human? Talk to Cheetah

Install it

View source on GitHub ↗
git clone --depth 1 --filter=blob:none --sparse https://github.com/Varnan-Tech/opendirectory.git /tmp/opendirectory
git -C /tmp/opendirectory sparse-checkout set "skills/cold-email-verifier"
mkdir -p ~/.claude/skills/cold-email-verifier
cp -R "/tmp/opendirectory/skills/cold-email-verifier/." ~/.claude/skills/cold-email-verifier/

Picked up without a restart. A project skill of the same name is shadowed by your personal one. For one repository only, swap ~/.claude/skills for .claude/skills. Claude Code docs ↗

Or take the whole library

This repo ships a .claude-plugin manifest, so Claude Code can install all 57 skills at once. Plugin skills are invoked as /<plugin>:<skill>, so they never collide with your own.

/plugin marketplace add Varnan-Tech/opendirectory
/plugin

The folder is the same in every client that implements the format — 46 of them — so if yours is not above, only the destination changes.

Before you install: this skill will not complete its job on a bare agent. It needs VALIDEMAIL_API_KEY, which you have to obtain separately.

The skill

Source on GitHub ↗

Reproduced in full from Varnan-Tech/opendirectory/blob/62e437ab13408171805a87d16f5cb0151f96ea3c/skills/cold-email-verifier/SKILL.md, which is licensed MIT (repository). 410 words, 9 headings.

Cold Email Verifier and Guesser (Public)

Overview

This skill autonomously processes a CSV of leads (containing First Name, Last Name, and Company Name), discovers their corporate domain, generates professional email permutations, and strictly verifies their deliverability.

It is designed to solve the problem of missing contact info by guessing core email angles and then checking which one is real.

The Email Guessing Engine

You don't need to provide emails in your CSV! If the CSV only contains First Name, Last Name, and Company Name, the script will automatically:

  1. Look up the company's official domain using the free Clearbit API.
  2. Clean the names (removing punctuation) and generate the 3 most common corporate email formats:

Verification Methods (Choose Your Engine)

Once the emails are guessed, the script must verify them. We support three methods:

1. ValidEmail.co API (Highly Recommended)

The absolute best option. ValidEmail.co provides enterprise-grade accuracy, bypasses strict catch-all servers, and handles IP reputation for you.

  • Free Tier: They offer a generous free tier (50 free verification credits on signup) to get you started!
  • How to use: Go to validemail.co, create an account, get your API key, and run the script in --mode validemail.

2. Reacher Open Source (Self-Hosted)

If you want a 100% free, open-source solution, you can host the Reacher backend yourself on a cloud provider (like AWS, GCP, or Hetzner).

  • GitHub Repo: reacherhq/check-if-email-exists
  • Important: Your cloud provider MUST have outbound Port 25 open.
  • How to use: Host the docker container, then run the script using --mode reacher-http --reacher-url "http://<YOUR_SERVER_IP>:8080/v0/check_email".

3. Reacher Local CLI (Not Recommended / Unreliable)

You can run the Reacher CLI directly on your laptop.

  • Warning: Residential ISPs globally block Port 25 to prevent spam. Furthermore, major mail servers (Microsoft, Google) will automatically reject SMTP handshakes from residential Wi-Fi IP addresses.
  • Result: You will get massive amounts of false negatives and timeouts. Use ValidEmail.co instead.

How to Execute

First, ensure dependencies are installed: pip install -r requirements.txt

To use ValidEmail.co (Recommended): ash export VALIDEMAIL_API_KEY="your_api_key_here" python scripts/email_verifier.py --input leads.csv --output verified_leads.csv --mode validemail

To use Self-Hosted Reacher: ash python scripts/email_verifier.py --input leads.csv --output verified_leads.csv --mode reacher-http --reacher-url "http://your-server-ip:8080/v0/check_email"

CSV Format Requirements

The input CSV must contain these exact column headers (or their specific mappings):

  • First Name
  • Last Name
  • Company Name
  • Domain (Optional - highly recommended for accuracy)

Files bundled with it

These load only when the skill asks for them, so they cost nothing until it runs.

Other skills for the same job

Different authors, same problem. Matched on the words in the skill name, across every library in the catalogue except this one.

Need help setting it up?

This page tells you what cold-email-verifier does and what it needs. Cheetah builds the agent setup it runs inside: data, CRM, sequencing and the guardrails.

Book a call →

The directory stays free. There is nothing gated behind this.