---
title: "Pi-hole AI Blocklist Blocks Claude Desktop (ERR_CONNECTION_REFUSED)"
domain: troubleshooting
category: networking
tags: [pihole, dns, claude, adlist, blocklist, ai-blocklist]
status: published
created: 2026-04-22
updated: 2026-04-22
---
# Pi-hole AI Blocklist Blocks Claude Desktop (ERR_CONNECTION_REFUSED)

## 🛑 Problem

Claude Desktop throws a `[remoteMarketplaceClient] transport error: net::ERR_CONNECTION_REFUSED` error when attempting to install or load a plugin. The app itself loads fine and API calls work, but the marketplace client silently fails.

---

## 🔍 Diagnosis

### Step 1 — Check the Pi-hole query log for claude.ai

```bash
sudo pihole-FTL sqlite3 /etc/pihole/pihole-FTL.db \
  "SELECT datetime(timestamp, 'unixepoch', 'localtime') as time, domain, status \
   FROM queries \
   WHERE domain LIKE '%anthropic%' OR domain LIKE '%claude%' \
   ORDER BY timestamp DESC LIMIT 50;"
```

Look for `claude.ai` entries with **status `1`** (gravity/adlist block). Status `2` or `3` means it's resolving fine.

**FTL status codes relevant here:**

| Status | Meaning |
|--------|---------|
| 1 | Blocked — gravity (adlist) |
| 2 | Forwarded (allowed) |
| 3 | Cached (allowed) |
| 4 | Blocked — regex domainlist |
| 5 | Blocked — exact domainlist |

### Step 2 — Identify which adlist is blocking it

```bash
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "SELECT a.address, a.comment \
   FROM gravity g \
   JOIN adlist a ON g.adlist_id = a.id \
   WHERE g.domain = 'claude.ai';"
```

**Root cause:** `claude.ai` appears in AI-focused blocklists because they target AI scraper and training crawlers by domain. Claude Desktop's marketplace client makes outbound requests to `claude.ai`, which Pi-hole resolves to `0.0.0.0` in NULL blocking mode — resulting in `ERR_CONNECTION_REFUSED` at the TCP layer.

Known adlists that include `claude.ai`:
- **uBlockOrigin HUGE AI Blocklist** (`laylavish/uBlockOrigin-HUGE-AI-Blocklist`)
- **Super SEO Spam Suppressor** (`NotaInutilis/Super-SEO-Spam-Suppressor`)

---

## ✅ Fix

Add `claude.ai` as an exact whitelist entry (type 0) in Pi-hole's domainlist. This overrides any gravity block.

```bash
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "INSERT OR IGNORE INTO domainlist (type, domain, enabled, comment) \
   VALUES (0, 'claude.ai', 1, 'Whitelisted — blocked by AI/SEO adlists, needed for Claude Desktop marketplace client');"
```

Then reload DNS to apply:

```bash
sudo pihole reloaddns
```

### Verify the whitelist entry is active

```bash
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "SELECT domain, type, enabled, comment FROM domainlist WHERE domain = 'claude.ai';"
```

Expected output:
```
claude.ai|0|1|Whitelisted — blocked by AI/SEO adlists, needed for Claude Desktop marketplace client
```

---

## 🔁 Why This Happens

Pi-hole in NULL blocking mode resolves blocked domains to `0.0.0.0`. When Claude Desktop's marketplace client tries to connect to `claude.ai`, the TCP handshake to `0.0.0.0` is immediately refused by the OS — producing `ERR_CONNECTION_REFUSED` rather than a timeout or DNS error. This makes it look like a network or server issue rather than a DNS block.

AI-focused blocklists cast a wide net and include domains like `claude.ai` alongside actual AI scraper hostnames. The fix is a precision whitelist entry rather than removing the adlist.

---

## ⚠️ Note on the Custom Domainlist

`claude.ai` may also appear as an accidental **exact deny** entry in the Pi-hole custom domainlist if it was added via "Block" in the Pi-hole query log UI. This compounds the adlist block. Clean the domainlist if needed:

```bash
# Check for exact deny entries
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "SELECT id, domain, type, enabled FROM domainlist WHERE domain = 'claude.ai';"

# Remove an unwanted deny entry (type 1 = exact deny)
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "DELETE FROM domainlist WHERE domain = 'claude.ai' AND type = 1;"

sudo pihole reloaddns
```

---

## 🔎 Quick Reference

```bash
# Check if claude.ai is blocked
sudo pihole-FTL sqlite3 /etc/pihole/pihole-FTL.db \
  "SELECT datetime(timestamp, 'unixepoch', 'localtime'), domain, status \
   FROM queries WHERE domain = 'claude.ai' ORDER BY timestamp DESC LIMIT 10;"

# Find which adlist is blocking it
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "SELECT a.address FROM gravity g JOIN adlist a ON g.adlist_id = a.id \
   WHERE g.domain = 'claude.ai';"

# Whitelist it
sudo pihole-FTL sqlite3 /etc/pihole/gravity.db \
  "INSERT OR IGNORE INTO domainlist (type, domain, enabled, comment) \
   VALUES (0, 'claude.ai', 1, 'Claude Desktop marketplace client');"

# Reload
sudo pihole reloaddns
```