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Nginx Conflicting Server Block Detector

Find server blocks that collide on the same server_name and listen pair.

Runs entirely in your browser - nothing is uploaded and no cloud connection is made.
Your conflicting server block findings will appear here.
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server blocks
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conflicts

About Nginx Conflicting Server Block Detector

Nginx only honours one server block per unique domain and listen combination, so a second identical block silently overrides or conflicts with the first depending on load order. The Conflicting Server Detector parses a pasted configuration, enumerates every server block and flags any two that share both the same server_name and the same listen value before they reach your server.

At the heart of the configuration are a handful of directives. server defines a virtual host that nginx selects by name and port. listen sets the address and port a server block answers on. server_name sets the Host header values that route a request to this block. location scopes directives to a matching URI path inside a server block. include pulls in external files, which can hide duplicate blocks across paths. root sets the document root served when a request matches the block. Together they shape how the server behaves, and the tool assembles them in the right context so the result is valid on the first try.

Common mistakes are easy to make. Two server blocks with the same server_name and listen make nginx pick one non-deterministically, so the detector flags the overlap. A wildcard server_name can mask a more specific block, producing a conflict you did not intend. Using include to pull config from many files spreads duplicate blocks across paths the detector cannot see unless pasted together. Forgetting the default_server keyword leaves a tie unresolved when multiple blocks match the same request. The generator anticipates each of these and either sets a safe default or rejects the input with a clear message before anything is written to your clipboard.

Validation is strict because small configuration errors fail in subtle ways. Every input is checked for plausibility, and after the block is assembled it is re-parsed by a built-in tokenizer so unbalanced braces, missing semicolons or stray characters cannot reach your clipboard. Stat cards report line and block counts, and copy, download and print exports are one click away. Everything runs in your browser; nothing you type is transmitted to any server.

In practice this block drops into any standard nginx install. Save the output as a file under /etc/nginx/conf.d/ (or sites-available with a symlink), run nginx -t to confirm the syntax, then reload with nginx -s reload. Because the generator emits a single, self-contained server block with no hidden dependencies, it composes cleanly with your existing caching, logging and security configuration without directive collisions.

Beyond producing correct config, the tool is a reference you can read back and learn from. Each control maps to a real nginx directive, the sample button shows a complete working block in seconds, and clearing the form resets every field to its safe default. Standardising on a generator like this removes per-developer variation, keeps your configuration readable, and gives you a repeatable, auditable setup that passes nginx -t on the first try.

When something looks wrong in production, the first move is always to re-run nginx -t and inspect /var/log/nginx/error.log; most failures surface there with a line number. The access log records every request, so a sudden spike or a wall of 499 responses points straight at backend or timeout problems the generator helps you avoid in the first place.

This server block is designed to sit alongside - not fight - your other configuration. Because it declares its own server_name and a single, self-contained set of directives, you can drop it into conf.d without worrying about collisions with global caching, logging or security snippets that live elsewhere in the nginx tree.

For a production site, pair this block with TLS termination: serve on 80 for the redirect or health checks, and place the encrypted listener (or a front-end load balancer / CDN) in front so clients always speak HTTPS. The generator keeps that boundary clean so the two layers compose instead of overlapping.

If a change ever needs to be undone, the output is plain text you control: delete the file from conf.d, re-run nginx -t, and reload. There is no database and no hidden state, so rolling back is as simple as restoring the previous version from version control or your own backup.

Performance and correctness both benefit from explicit configuration. Defaults baked into the generator reflect current best practice rather than decades-old forum snippets, so the block you ship today will not surprise you with deprecated directives or insecure fallbacks six months from now.

For teams, a generated block is also documentation. New engineers can read the exact directives in place, compare them against the sample, and learn the relevant nginx behaviour without reverse-engineering a hand-maintained file that drifted from its original intent.

Features

  • server - defines a virtual host that nginx selects by name and port.
  • listen - sets the address and port a server block answers on.
  • server_name - sets the Host header values that route a request to this block.
  • location - scopes directives to a matching URI path inside a server block.
  • include - pulls in external files, which can hide duplicate blocks across paths.
  • root - sets the document root served when a request matches the block.
  • Self-verifying output re-parsed before display.
  • Copy, Download and Print exports.
  • Load-sample button fills realistic values.
  • Statistics cards for quick checks.
  • Runs entirely in your browser - nothing uploaded.

How to Use

  1. Paste your full nginx configuration into the text area.
  2. For a quick start click Load sample to see a conflicting pair.
  3. Click Run check to parse and analyse the configuration.
  4. Review the findings list of conflicting block line numbers.
  5. Note the shared domain and listen value reported for each conflict.
  6. Remove or rename one side of each conflict.
  7. Re-paste and re-check until no conflicts remain, then run nginx -t.

Examples

Example 1 - Identical domain and port two server blocks both on example.com:80 are flagged as a conflict.

Example 2 - Clean config distinct domains produce no conflict finding.

Example 3 - Multiple server_names a block sharing one of several names still conflicts with the other block.

Example 4 - Wildcard masking a block without an explicit host falls back to default and still collides.

Example 5 - No listen clause blocks without listen fall back to default and are still compared.

Benefits

  • Rapidly surfaces hidden duplicate server blocks.
  • Prevents silent config override in production.
  • Parses real nginx syntax, not fragile line matching.
  • Reports exact line numbers for fast fixes.
  • Handles multiple domains and listen values per block.
  • Runs locally with no upload of your configuration.

Frequently Asked Questions

What counts as a conflict?
A pair of server blocks sharing the same server_name and the same listen value. Nginx can only honour one of them reliably.
Does order matter?
Nginx chooses one block, but the choice is fragile, so the detector reports the overlap regardless of which block is listed first.
Will it catch wildcard overlaps?
If a name matches exactly it is reported; overlapping wildcards that resolve to the same host still need manual review.
What if a block has no listen?
It is treated as the default listener and still compared against the others for name and listen collisions.
Can I check included files?
Paste the fully expanded configuration including included files for complete coverage across every path.
Does it rewrite my config?
No, it only reports findings; you decide which block to rename or remove.
Is my config uploaded?
No, everything runs in your browser and nothing is transmitted to any server.
What about IPv6 listen values?
IPv6 listen values are compared as plain strings, so identical ones are flagged just like IPv4.