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+# pkg-config {#sec-pkg-config}
+
+*pkg-config* is a unified interface for declaring and querying built C/C++ libraries.
+
+Nixpkgs provides a couple of facilities for working with this tool.
+
+## Writing packages providing pkg-config modules {#pkg-config-writing-packages}
+
+Packages should set `meta.pkgConfigModules` with the list of package config modules they provide.
+They should also use `testers.testMetaPkgConfig` to check that the final built package matches that list.
+Additionally, the [`validatePkgConfig` setup hook](https://nixos.org/manual/nixpkgs/stable/#validatepkgconfig), will do extra checks on to-be-installed pkg-config modules.
+
+A good example of all these things is zlib:
+
+```
+{ pkg-config, testers, ... }:
+
+stdenv.mkDerivation (finalAttrs: {
+  ...
+
+  nativeBuildInputs = [ pkg-config validatePkgConfig ];
+
+  passthru.tests.pkg-config = testers.testMetaPkgConfig finalAttrs.finalPackage;
+
+  meta = {
+    ...
+    pkgConfigModules = [ "zlib" ];
+  };
+})
+```
+
+## Accessing packages via pkg-config module name {#sec-pkg-config-usage}
+
+### Within Nixpkgs {#sec-pkg-config-usage-internal}
+
+A [setup hook](#setup-hook-pkg-config) is bundled in the `pkg-config` package to bring a derivation's declared build inputs into the environment.
+This will populate environment variables like `PKG_CONFIG_PATH`, `PKG_CONFIG_PATH_FOR_BUILD`, and `PKG_CONFIG_PATH_HOST` based on:
+
+ - how `pkg-config` itself is depended upon
+
+ - how other dependencies are depended upon
+
+For more details see the section on [specifying dependencies in general](#ssec-stdenv-dependencies).
+
+Normal pkg-config commands to look up dependencies by name will then work with those environment variables defined by the hook.
+
+### Externally {#sec-pkg-config-usage-external}
+
+The `defaultPkgConfigPackages` package set is a set of aliases, named after the modules they provide.
+This is meant to be used by language-to-nix integrations.
+Hand-written packages should use the normal Nixpkgs attribute name instead.