// find duplicate & conflicting port assignments instantly
Instantly detect duplicate or overlapping port assignments in config files, docker-compose, nginx, .env, and any text. Free, browser-based, no upload.
No conflicts detected yet
Paste your config and click Check ConflictsPaste any config file content — docker-compose, nginx, .env, Procfile, or plain text containing port numbers.
The tool scans every line, extracts port assignments, and groups them by port number.
Conflicts are highlighted in red. All detected ports are listed with their source lines for easy debugging.
Port Conflict Checker scans any text-based config file and extracts all port assignments. It then identifies ports that appear more than once — indicating a potential conflict where two services would compete for the same port.
Everything runs in your browser. Your config is never sent to a remote server.
Any plain-text file containing port numbers. This includes docker-compose.yml, nginx.conf, apache.conf, .env, Procfile, Kubernetes manifests, shell scripts, and more. The tool uses pattern matching rather than strict parsing, so it works on almost any format.
It scans each line for common patterns: HOST:CONTAINER mappings (docker), port: VALUE, listen PORT (nginx), EXPOSE PORT (Dockerfile), and PORT=VALUE (env vars). Lines starting with # or // are treated as comments and skipped.
No. All processing happens in your browser via JavaScript. Nothing is stored, logged, or transmitted. You can safely paste sensitive configs including passwords, keys, or internal hostnames.
A conflict is flagged when the same port number appears more than once in the same input — on different lines or in different services. This usually means two services would attempt to bind the same host port, which causes a startup error.
Yes. For a mapping like 8080:80, the tool tracks port 8080 as the host port — the one that must be unique on your machine. The container port (80) is internal and can be reused across services without conflict.
The tool flags any port that appears more than once regardless of whether it's a "well-known" port. Multiple services binding port 80 is still a conflict. If you intentionally reuse a port (e.g., load balancer upstream), you can ignore the flag.
Yes — just paste the contents of multiple files together. The tool treats the entire input as one document and detects conflicts across all pasted content. This is useful for checking an entire project's worth of service configs at once.
Valid TCP/UDP ports: 1 through 65535. Numbers outside this range are ignored. Well-known ports (1–1023) are highlighted with a badge to help you quickly spot privileged port usage.
A Port Conflict Checker is a developer utility that scans configuration files and identifies cases where two or more services are assigned the same network port. Port conflicts are among the most common and frustrating issues when running containerized applications, microservices, or local development stacks. Instead of waiting for a cryptic "address already in use" error at runtime, you can catch conflicts before they happen.
This tool works with any plain-text configuration format — docker-compose.yml, nginx.conf, Apache virtual host files, .env files, Procfiles, Kubernetes manifests, and more. Paste the content, click check, and instantly see every port assignment grouped and flagged.
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Every network port can only be bound by one process at a time on a given host interface. When two services try to listen on the same port, only the first one succeeds — the second crashes with a binding error. This becomes especially problematic in Docker Compose stacks where multiple services map container ports to host ports, microservice architectures where dozens of services run simultaneously, monorepos where separate apps each define their own port in .env files, and local development environments where developers run multiple projects simultaneously.
The tool applies pattern-matching rules to each line of your input, ignoring comment lines that start with # or //. It recognizes docker-style host:container mappings, port: VALUE YAML assignments, nginx listen PORT directives, Dockerfile EXPOSE PORT instructions, and PORT=VALUE environment variable declarations.
Once all port assignments are extracted, the tool groups them by port number and flags any port that appears more than once. The result includes the exact line numbers and content of every occurrence, making it trivial to locate and fix the problem.
Docker Compose conflicts are the most frequent scenario. A developer adds a new service to docker-compose.yml and accidentally reuses a host port already assigned to another service. The error only appears when running docker-compose up, often deep in startup logs. The Port Conflict Checker catches this before you even run the stack.
Nginx virtual host collisions occur when configuring multiple sites on a single nginx server. Each listen directive must be unique, or use server_name to differentiate. Paste your entire nginx config and the tool will immediately show if any two server blocks listen on the same port.
Multi-repo .env drift happens in polyrepo setups where each service has its own .env file defining a PORT variable. Over time these diverge in developers' local environments. Pasting all .env contents together into the checker reveals overlaps before they cause CI or local dev failures.
TCP and UDP ports are divided into three ranges. Well-known ports (0–1023) are reserved for system services like port 80 (HTTP), 443 (HTTPS), 22 (SSH), 3306 (MySQL), and 5432 (PostgreSQL) — binding these requires root privileges. Registered ports (1024–49151) are assigned to specific applications by convention, including 3000 (Node.js/React dev), 8080 (alternative HTTP), 6379 (Redis), and 27017 (MongoDB). Dynamic ports (49152–65535) are ephemeral ports generally safe for internal services.
Maintaining a port registry document — even a simple markdown table — is a low-effort practice that pays dividends in larger projects. Document which service owns which port, and update it whenever a new service is added. Combine this with a pre-commit check using a tool like this Port Conflict Checker to automate enforcement.
For Docker Compose specifically, consider using environment variables for port numbers rather than hardcoding them. Define all port values in a single .env file at the project root, reference them in docker-compose.yml with ${SERVICE_PORT} syntax, and run the conflict checker against the .env file as part of your onboarding checklist. This single-source-of-truth approach eliminates the entire class of hardcoded port conflicts.