How to Add Inbox Placement Testing to Claude Desktop in 2 Minutes

This article does exactly what the title promises. You'll paste one JSON block into a config file, restart Claude Desktop, and ask it to run a deliverability test. End result: Claude can see your inbox placement numbers, read the SPF/DKIM/DMARC verdict, and suggest fixes — without you leaving the chat window.

You will need

Claude Desktop installed, Node.js 20 or newer on your machine, and a free Inbox Check API key (the kind that starts with ic_live_). Nothing else.

What you get at the end

When the setup is done, the chat composer in Claude Desktop shows a small hammer icon. Clicking it lists the tools Claude can now call —start_test, get_test, check_auth, check_blacklist, list_providers. You type a sentence like "test deliverability for hello@myco.com" and Claude does the rest: kicks off the test, polls for completion, reads the verdict, summarises it, and suggests concrete DNS changes if anything is broken.

Step 1: find claude_desktop_config.json

Claude Desktop reads its MCP configuration from a JSON file that ships empty by default. The location depends on your OS:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
Windows: %APPDATA%\Claude\claude_desktop_config.json
Linux (community build): ~/.config/Claude/claude_desktop_config.json

If the file doesn't exist yet, create it. If it does exist and already has an mcpServers object, you'll merge the block below into it rather than replacing the whole file.

Step 2: paste the config block

Here is the full file contents for a fresh install. Replace the placeholder API key with your real one:

{
  "mcpServers": {
    "inbox-check": {
      "command": "npx",
      "args": ["-y", "ldm-inbox-check-mcp"],
      "env": {
        "INBOX_CHECK_API_KEY": "ic_live_REPLACE_ME"
      }
    }
  }
}

If you already have other MCP servers configured, just add the inbox-check entry inside the existing mcpServers object — don't replace the whole file.

Step 3: get your API key

Go to the Inbox Check dashboard at check.live-direct-marketing.online, sign in, and open the API Keys page. Click Create key, copy the ic_live_... string, and paste it into the INBOX_CHECK_API_KEY field in your config. Save the file.

Step 4: fully quit and relaunch Claude Desktop

This step catches people. Closing the window is not enough — Claude Desktop keeps running in the background. You need to fully quit:

macOS: Cmd+Q, or right-click the dock icon and choose Quit.
Windows: right-click the tray icon and choose Exit.

Relaunch. Open a new chat. You should see a small hammer or tool icon in the composer. Click it — the Inbox Check tools should be listed under their names.

Step 5: try the first prompt

Paste something like this into the chat:

Test deliverability for hello@myco.com with
subject "Welcome to MyCo" and this HTML:

<html><body><h1>Welcome!</h1>
<p>Thanks for signing up.</p></body></html>

When the test finishes, tell me what to fix.

Claude will ask permission to call the tool the first time — approve it. Then watch: it calls start_test, gets a test ID, polls get_test, and writes a summary like:

Your test finished. 17/20 inbox, 2/20 spam,
1/20 missing. SPF: pass. DKIM: no signature
found (this is why 2 went to spam). DMARC:
p=none, so receivers aren&apos;t quarantining,
just routing to spam at strict providers.

Fix DKIM first. Your mail is going via Google
Workspace — enable DKIM in Admin Console and
publish the selector at
google._domainkey.myco.com. Retest after DNS
propagation (usually 10-15 minutes).

Works on the free tier

You don't need a paid plan for any of this. The free tier of Inbox Check gives you enough tests per month to debug real problems. If you plug the same key into Claude Desktop, Cursor, and a CI script you share the same quota across all three.

A few prompts that work well

Once the hammer icon shows the tools, these all Just Work:

"Check if the IP 203.0.113.45 is on any blacklists."
"Look up SPF/DKIM/DMARC for news.brandx.com and tell me what's wrong."
"Which providers does Inbox Check currently support? I want to know whether Zoho is covered."
"Run a placement test for (paste template). After it finishes, open an issue in my mental to-do list with the top three fixes."

Troubleshooting

Hammer icon doesn't appear

Most likely cause: Claude Desktop wasn't fully quit. Force-quit and relaunch. Second: syntax error in the JSON — copy the block above exactly, paying attention to commas if you're merging into an existing file.

"Command not found: npx"

Install Node.js 20 or newer from nodejs.org. The npx binary ships with every recent Node version.

"401 unauthorized" on the first tool call

The API key is wrong, missing or has the placeholder still in place. Open the config file, confirm the ic_live_ prefix, save, fully quit Claude, relaunch.

Tool calls hang forever

Check you have outbound HTTPS to check.live-direct-marketing.online. On a corporate network this can be blocked — try a hotspot to confirm.

Frequently asked questions

Do I need to install ldm-inbox-check-mcp separately?

No. The npx -y prefix in the config tells Node to download it on first use. You never run npm install yourself.

Can I use this with a project claude.mcp file instead of the global one?

Claude Desktop currently reads only the global config. For per-project MCP, use Cursor or Claude Code — both honour workspace-level MCP settings.

Does Claude see my API key?

No. The key lives in the MCP server's environment only. The model sees tool outputs (test results, verdicts) but not the credential.

How many tests can I run from Claude Desktop?

Same limit as your Inbox Check plan — the free tier covers a few dozen per month, which is more than enough for interactive debugging. Claude won't burn tests in the background; it only runs one when you ask.

Add inbox placement testing to Claude Desktop in 2 minutes