The manifest file records the provenance of the packages that are installed in a profile managed by nix-env.

Here is an example of how this file might look like after installing hello from Nixpkgs:

  meta = {
    available = true;
    broken = false;
    changelog =
    description = "A program that produces a familiar, friendly greeting";
    homepage = "";
    insecure = false;
    license = {
      deprecated = false;
      free = true;
      fullName = "GNU General Public License v3.0 or later";
      redistributable = true;
      shortName = "gpl3Plus";
      spdxId = "GPL-3.0-or-later";
      url = "";
    longDescription = ''
      GNU Hello is a program that prints "Hello, world!" when you run it.
      It is fully customizable.
    maintainers = [{
      email = "";
      github = "edolstra";
      githubId = 1148549;
      name = "Eelco Dolstra";
    name = "hello-2.12.1";
    outputsToInstall = [ "out" ];
    platforms = [
    position =
    unfree = false;
    unsupported = false;
  name = "hello-2.12.1";
  out = {
    outPath = "/nix/store/260q5867crm1xjs4khgqpl6vr9kywql1-hello-2.12.1";
  outPath = "/nix/store/260q5867crm1xjs4khgqpl6vr9kywql1-hello-2.12.1";
  outputs = [ "out" ];
  system = "x86_64-linux";
  type = "derivation";

Each element in this list corresponds to an installed package. It incorporates some attributes of the original derivation, including meta, name, out, outPath, outputs, system. This information is used by Nix for querying and updating the package.