Claude Skills Guide

Claude Code Error Connection Refused Localhost Fix

Connection refused errors when Claude Code attempts to connect to localhost can halt your development workflow unexpectedly. This guide provides actionable solutions for developers and power users encountering this issue.

What Causes Connection Refused Errors

When Claude Code attempts to connect to a local service and receives a “connection refused” error, it means no service is listening on the target port. This differs from a timeout, which indicates the connection attempt stalled. With connection refused, the operating system actively rejected the connection attempt because nothing was accepting connections on that port.

These errors commonly occur in several scenarios: running Claude Code with the webapp-testing skill to test local development servers, using the supermemory skill with a local Redis instance, or connecting to local database services like PostgreSQL or MongoDB. Understanding which service Claude Code expects to find helps you apply the correct fix.

Diagnosing the Problem

The first step involves identifying which service Claude Code expects to find. Check the error message carefully—it typically specifies the port number and sometimes the service type. Common ports include 3000 (Next.js development servers), 5432 (PostgreSQL), 6379 (Redis), and 27017 (MongoDB).

Open a terminal and run the following command to check which services are currently listening on your machine:

# macOS and Linux
lsof -i -P | grep LISTEN

# Windows
netstat -ano | findstr "LISTENING"

This command reveals all ports currently accepting connections. If the expected service port does not appear in the output, the service either failed to start or is running on a different port than expected.

Fix 1: Starting the Required Service

The most straightforward solution involves ensuring the required service runs before Claude Code attempts to connect. Navigate to your project directory and start the development server:

# For Node.js projects
npm run dev

# For Python projects with Flask
python app.py

# For Ruby on Rails
rails server

# For Django
python manage.py runserver

After starting the service, verify it listens on the correct port by checking the output. Development servers typically display the URL and port in their startup messages. The webapp-testing skill expects the server to remain running during testing sessions.

Fix 2: Checking Port Configuration

Services sometimes use different ports than their defaults. React applications created with Create React App default to port 3000, but Next.js applications may use 3000, 3001, or other ports depending on availability. Verify your service configuration and update any relevant settings in your CLAUDE.md file.

To find the exact port your service uses, examine the startup output or check your package.json scripts:

# Check package.json for port configuration
cat package.json | grep -A 5 '"scripts"'

If your Next.js application runs on port 3001 instead of 3000, update any connection references accordingly. The frontend-design skill often generates code that assumes specific port configurations.

Fix 3: Firewall and Security Software

Security software sometimes blocks localhost connections, particularly on macOS and Windows. macOS includes built-in firewall functionality that may interfere with certain connection patterns. Windows Defender and third-party antivirus software also maintain network protection features.

To temporarily disable the macOS firewall for development purposes:

# Check firewall status
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate

# Disable firewall (not recommended for production)
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate off

For Windows, navigate to Windows Security > Firewall & network protection and temporarily disable the firewall for your network profile. Remember to re-enable firewall protection after debugging.

Fix 4: Using the Correct Hostname

Network configurations vary across operating systems and development environments. Some systems require explicit binding to localhost rather than 127.0.0.1. Verify your service binds to the correct interface:

# Check what your service is listening on
lsof -i :PORT_NUMBER

Replace PORT_NUMBER with the actual port from your error message. The output shows whether the service listens on 127.0.0.1, 0.0.0.0, or a specific IP address. Services bound to 0.0.0.0 accept connections from any interface, while 127.0.0.1 restricts connections to the local machine.

For containerized development environments, ensure your Docker or Kubernetes configurations expose the correct ports to the host system. The docker skill provides specific guidance for container networking.

Fix 5: Waiting for Service Readiness

Development servers require time to initialize before accepting connections. Claude Code may attempt to connect before your service becomes available, particularly with frameworks that perform hot reloading or compile-time optimizations.

Implement a readiness check in your workflow:

# Wait for port to become available
until nc -z 127.0.0.1 3000; do
  echo "Waiting for server..."
  sleep 2
done

echo "Server is ready!"

This bash snippet polls port 3000 every two seconds until the connection succeeds. Integration with the supermemory skill or other persistent connection handlers benefits from this approach.

Fix 6: Configuring Claude Code Timeout Settings

While connection refused errors differ from timeouts, adjusting connection behavior can help in edge cases. Set environment variables to modify how Claude Code handles network connections:

# Add to .zshrc or .bashrc
export ANTHROPIC_CONNECTION_RETRIES=3
export ANTHROPIC_CONNECTION_DELAY=1000

These settings configure retry attempts and delay between attempts in milliseconds. The tdd skill and other testing-focused skills particularly benefit from stable connection configurations.

Fix 7: Checking for Port Conflicts

Another service may already occupy the expected port. Kill the conflicting process or configure your service to use a different port:

# Find process using a specific port
lsof -i :3000

# Kill the process by PID
kill -9 PID_NUMBER

If you prefer using a different port, most frameworks accept a PORT environment variable:

PORT=3001 npm run dev

Prevention Strategies

Establish consistent practices to avoid connection refused errors in the future. Document required services in your project CLAUDE.md file so Claude Code understands startup dependencies:

# Project Requirements

This project requires the following services to be running:

- PostgreSQL on port 5432 (use `docker-compose up db`)
- Redis on port 6379 (use `docker-compose up redis`)
- Next.js dev server on port 3000 (use `npm run dev`)

Start services in order before beginning Claude Code sessions.

The supermemory skill can store these configurations across sessions, ensuring consistent project setup. For teams using the slack-gif-creator skill or other collaborative features, maintain shared service documentation.

Summary

Connection refused errors stem from services not running, incorrect ports, firewall interference, or binding configuration issues. Start by identifying which service Claude Code expects, verify its running status, and check network binding configurations. Most issues resolve by simply starting the required development server before beginning Claude Code sessions.

For complex multi-service projects, consider using docker-compose to manage dependencies and ensure all required services start together. The container skill provides detailed guidance for containerized development workflows.

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