htaccess to nginx conversion is not a line-for-line translation: Apache reads a per-directory .htaccess file at request time, while Nginx evaluates centralized configuration in server and location blocks before the rewrite engine runs, so even an identical regular expression can match a different string in the two systems. A converter that respects this gap translates only a narrow, well-understood subset of Apache directives into Nginx lines and reports every condition, unknown flag, or syntactically ambiguous rule with its original line number instead of inventing plausible-but-wrong Nginx configuration. The practical scope covers simple RewriteRule patterns with the bracketed flag set L, R, R=301 or R=302, the directory-listing disablement Options -Indexes, a document-root ErrorDocument 404, and a quoted X-Robots-Tag Header set value. Anything else — RewriteCond rules, unfamiliar flags such as QSA, END, F, G, B or NC, the no-substitution dash target, authentication, proxy logic or CMS front-controller rewrites — is left to a human migration against the Apache and Nginx manuals. The result is a review-ready fragment, never a complete nginx.conf.
That difference between request models is the reason any honest explanation has to start with what the converter does not claim. Apache walks the URL, descends into each directory, and re-reads every .htaccess it finds (unless AllowOverride None is set). Nginx does the equivalent once, in memory, against the configuration files that were loaded at startup or after a reload. A rule that works in a nested directory on Apache may sit in a totally different location on Nginx, and a regex that captures ^old/(.*)$ on Apache sees a path with the directory prefix already removed, while Nginx sees a URI that begins with a slash.
Why .htaccess and Nginx Are Not Interchangeable
The two engines grew up around different assumptions. Apache's per-directory model means a CMS can ship a .htaccess inside its installation directory and have its rewrite rules applied without touching the main server config, which is convenient for shared hosting but costly on every request. Nginx inverts that trade-off: configuration is loaded once and matched against the incoming URI in a tree of server and location blocks, which is fast and predictable but means there is no file the application can drop in to change routing later.
Three practical consequences follow for anyone trying to migrate:
- Match string differs. An Apache RewriteRule in a document-root .htaccess typically sees a path with the document-root prefix already removed, so patterns commonly begin with a caret but no slash. Nginx rewrite directives operate on the URI, which always starts with /. The converter inserts that leading slash for supported root-context patterns; that is a documented scope assumption, not a universal transformation for nested files or Alias mappings.
- Processing model differs. Apache can chain RewriteRule and RewriteCond directives across many directives; Nginx has only one rewrite directive per location, with if blocks that have well-known footguns. A one-to-one port usually collapses several Apache lines into one Nginx rule, which is part of why automatic translation is risky.
- AllowOverride is not a setting on Nginx. There is no per-directory override at all. Anything you wanted .htaccess to do must be moved into the main configuration in the right context.
That context matters for every line the htaccess to Nginx Converter emits.
The Supported Subset the Converter Translates
The converter is built around a deliberate, narrow contract: it translates only what it can translate without guessing. That contract covers four families of input.
- Simple RewriteRule patterns with a bounded flag set. The bracketed flag list must contain only L, R, R=301 or R=302, in any combination. Anything else in the flag brackets stops conversion for that rule.
- Options -Indexes. A single directive that disables Apache's directory listing maps to autoindex off; in Nginx.
- Local ErrorDocument 404 paths. A path-style local 404 becomes the equivalent error_page 404 /path; line in Nginx.
- Quoted X-Robots-Tag Header set values. A quoted Header set X-Robots-Tag "noindex" becomes an add_header X-Robots-Tag "noindex"; line.
Everything else — other status codes, external error document URLs, conditional headers, environment variables, authentication blocks, proxy directives, or any <IfModule> container — falls outside the contract. The tool processes input in the browser and does not send the pasted excerpt to a server.
How RewriteRule Flags Map Across Engines
The bracketed flag list at the end of an Apache RewriteRule is the densest source of mistakes during migration. Each flag changes the semantics of the rewrite, and Nginx has its own names for the closest equivalents.
| Apache Flag | Nginx Translation | Behavior Note |
|---|---|---|
| L | last | Stops the current rewrite and re-evaluates location against the rewritten URI. |
| R | redirect | Temporary redirect, HTTP 302 by default; not cached by browsers. |
| R=301 | permanent | Browser- and intermediary-cacheable; use only after thorough testing. |
| R=302 | redirect | Explicit temporary redirect; same caching class as bare R. |
| QSA | (warning, suppressed) | Query-string append behavior cannot be erased safely without context. |
| END | (warning, suppressed) | No direct Nginx equivalent; do not map to last. |
| F / G | (warning, suppressed) | Forbidden / gone access flags need separate Nginx return rules. |
| B | (warning, suppressed) | Backreference-escape behavior differs between the two regex engines. |
| NC | (warning, suppressed) | Nginx uses PCRE; flag handling and case sensitivity differ. |
The Apache RewriteEngine On line is ignored. Comments are preserved. Patterns that already begin with / are passed through without a second slash being added.
The Three Non-Rewrite Mappings the Tool Handles
Outside the rewrite module, only three directives get a direct mapping, and each one preserves the path or value as written.
Options -Indexes disables Apache's automatic directory listing and becomes autoindex off; in Nginx, which lives in the http, server, or location context. ErrorDocument 404 /errors/404.html maps to error_page 404 /errors/404.html; — the local path is preserved as the Nginx error_page argument, and the file still has to live somewhere Nginx can serve it. A quoted Header set X-Robots-Tag "noindex, nofollow" becomes add_header X-Robots-Tag "noindex, nofollow" always;; the quoted value is preserved verbatim, but Nginx's add_header inherits only from the matching block, which catches a lot of migrations off guard. Other status codes, external error document URLs, conditional headers, and Header directives with env=, setenvif or RequestHeader are outside the supported set and must be ported manually.
What the Tool Refuses to Translate (and Why)
Several categories of input produce warnings and no output, which is the point.
- RewriteCond lines. Apache conditions can inspect HTTPS state, host names, file existence, directories, query strings, headers, and captured groups, in an order that depends on where the rule sits in the directory tree. The tool reports each one with its line number and suppresses any RewriteRule that follows it, rather than emitting an unconditional redirect that could change traffic, create a loop, or expose a route that was supposed to be gated.
- Unknown or risky flags. QSA, END, F, G, B, NC and similar flags each carry context-dependent behavior. The tool stops conversion for that rule instead of guessing.
- The dash no-substitution target. An Apache rule like RewriteRule . - [F] modifies request handling without changing the URI; a literal dash is not a safe Nginx replacement.
- Anything outside the supported directive subset. Authentication, authorization, hotlink protection, proxy logic, environment variables, and CMS front-controller rules are engineering work, not text replacement.
A converter that silently writes plausible-looking but non-equivalent configuration is more dangerous than one that leaves explicit work behind. The line-numbered warnings are the contract.
Turning the Output Fragment Into a Working Config
The converter emits lines, not a nginx.conf. Assembling those lines into something you can actually load follows a predictable order.
- Back up the active Nginx configuration before opening any file. Keep an open recovery session, because a failed reload on a public server is a downtime event.
- Decide the right context for each emitted line. Redirects and rewrites almost always go inside a server block or a specific location block; autoindex off; can go http-, server- or location-wide; error_page belongs in http, server, or location depending on scope.
- Define listen, server_name, the document root, TLS, PHP or proxy routing, and logs around the fragment. None of those come from the converter.
- Run nginx -t against the assembled file. A passing test confirms that the syntax is valid for the modules you have compiled in; it does not confirm the rules behave as intended.
- Stage representative requests: old URL, new URL, query-string variations, alternate host names, HTTP and HTTPS. Confirm the response Location header from the server, not the address bar of a browser that may have cached a previous redirect.
- Reload with nginx -s reload only after staging passes. If staging fails, restore from backup and investigate; do not assume the converter output was wrong by itself — the context placement is part of the work.
For a deeper reference of supported rules, flags, and warning categories, the htaccess to nginx cheat sheet collects the same scope assumptions in one place.
Testing Redirects Safely Before Going Permanent
Permanent redirects are cached. A browser that sees 301 Moved Permanently will remember the mapping and apply it to the next request even if the server later changes its mind, and intermediaries like CDNs and corporate proxies can hold on to them longer than expected. That is why the converter maps R=301 to permanent but the explanation of the conversion is incomplete without a testing protocol.
Start with R or R=302, which translate to Nginx's redirect and behave like 302 responses. Hit each old URL with a tool that does not cache aggressively — curl -I is the common choice — and confirm the Location header points exactly where you expect, including query strings and trailing slashes. Test the same path over HTTPS and HTTP if both are live. Test alternate host names if the site is reachable by more than one. Only after staging confirms every old URL resolves correctly should the rules be switched to permanent, at which point the cache impact becomes permanent too.
For the underlying mechanics, the Apache mod_rewrite introduction documents what each Apache flag actually does, and the Nginx core error_page reference documents where error_page can live. Reading both for any rule that affects traffic flow is part of the contract — paste, review, test, then reload, in that order.