Temporarily install any package using nix shell nixpkgs#<PACKAGE_NAME> - this can be e.g. useful if you accidentally removed home-manager from your packages on a non-NixOS machine.

• if you need multiple packages, you can do nix shell nixpkgs#{<pkg1>,<pkg2>,<pkg3>}.
• you can set nix.registry to add more flakes to your registry. I use this to add a n shorthand to nixpkgs, which allows me to do nix shell n#{<pkg1>,<pkg2>,<pkg3>}.

Alternatively, use comma

• More info on nix [...] commands: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix
• some examples:
  • nix flake update <input-name> lets you update a specific input only.
  • nix repl <your flake path> gives quick insight into your written configuration.
  • nix eval <your flake path>#<config attribute> quickly returns an attribute in your written configuration
  • nix fmt formats your flake using the formatter specified under formatter in your flake.nix

When you are trying to setup a new configuration part, GitHub code search can really help you to find a working configuration. Just filter for .nix files and the options you are trying to set up.

getting packages at a different version than your target (or not packaged at all) can be done in most cases easily with fetchFromGithub (https://ryantm.github.io/nixpkgs/builders/fetchers/)

you can easily install old revisions of packages using https://lazamar.co.uk/nix-versions/. You can conveniently spawn a shell with a chosen package available using vershell <NIXPKGS_REVISION> <PACKAGE>. Just make sure to pick a revision that has flakes enabled, otherwise you will need the legacy way of spawning the shell (see the link for more info)

when developing modules in a dev branch of another flake, you can use --override-input to temporarily use the local directory as the flake source.

including nixosConfig ? config in your module arguments is a smart way of enabling a module to pull in config from NixOS or home-manager config, no matter if it is a NixOS system or not.

you can have a quick CLI evaluation for nix commands with e.g. nixpgks.lib available using nix-instantiate --strict --eval --expr "let lib = import <nixpkgs/lib>; in <expression>".

if you are looking for a specific library, nix-locate makes it easy to look for them.

to look at the dependencies pulled in by a tool, use nix-tree

• to find out which derivation uses another derivation, use nix store --query --referrers <derivation>

to get a neat overview of your config changes in recent generations, use nix profile diff-closures --profile /nix/var/nix/profiles/system

• to get instead the changes since the last boot, use nix profile diff-closures /run/*-system
• if you just need the generation numbers, use sudo nix-env --list-generations --profile /nix/var/nix/profiles/system
• to then switch to another generation, you can use sudo nix-env --switch-generation <generation number> -p /nix/var/nix/profiles/system followed by sudo /nix/var/nix/profiles/system/bin/switch-to-configuration switch

These links are your best friends:

• The nix documentation: https://nix.dev/
• The nixpkgs reference manual: https://nixos.org/manual/nixpkgs/unstable/#buildpythonapplication-function
  • the nixpkgs repository - especially useful to look at the various READMEs that are in various places in the repository (find using GitHub code search) as well as the issues and PRs pages
  • and the nixpkgs Pull Request Tracker
• The NixOS manual: https://nixos.org/manual/nixos/stable/
• The NixOS package search: https://search.nixos.org/packages
  • and the nix package version search: https://lazamar.co.uk/nix-versions/
• The NixOS option search https://search.nixos.org/options
• mipmip's home-manager option search: https://mipmip.github.io/home-manager-option-search/
• Alan Pearce's nix-darwin search: https://searchix.alanpearce.eu/options/darwin/search (which supports all of the other versions as well :o)
• For the above, you can use the CLI tool manix
• Nix function search: https://noogle.dev/
• Search for nix-community options: https://search.nüschtos.de/

But that is not all:

• Some nix resources
  • A tour of Nix: https://nixcloud.io/tour/
  • The Nix One Pager: https://github.com/tazjin/nix-1p
  • another one page introduction: https://learnxinyminutes.com/nix/
  • a very short introduction to Nix features: https://zaynetro.com/explainix
  • introductory nix article: https://medium.com/@MrJamesFisher/nix-by-example-a0063a1a4c55
  • and another one: https://web.archive.org/web/20210121042658/https://ebzzry.io/en/nix/#nix
  • How to learn nix: https://ianthehenry.com/posts/how-to-learn-nix/
  • the Nix Cookbook: https://github.com/functionalops/nix-cookbook?tab=readme-ov-file
  • and the Nix Pills: https://nixos.org/guides/nix-pills/
• Some resources on flakes
  • Why to use flakes and introduction to flakes: https://www.tweag.io/blog/2020-05-25-flakes/
  • The NixOS & Flakes Book
  • and Wombat's book
  • as well as Ekala's book
  • or the Zero to Nix series
  • last but not least, NixOS in Production
  • Practical nix flakes article: https://serokell.io/blog/practical-nix-flakes
• A bit on Overlays:
  • Overview on overlays: Mastering Nixpkgs overlays article
  • Some examples on best practices: Do's and Don'ts of overlays
  • Blog article about overrides: https://bobvanderlinden.me/customizing-packages-in-nix/#using-modified-packages
• Also useful is the official NixOS Wiki
  • there is also the unofficial NixOS Wiki that tends to be a bit outdated, use with care

Some resources for specific nix tools:

• Flake output reference: https://nixos-and-flakes.thiscute.world/other-usage-of-flakes/outputs
• You can find public repositories with modules at https://nur.nix-community.org/ (you should check what you are installing however):
  • I like to use this for rycee's Firefox extensions: https://nur.nix-community.org/repos/rycee/
• List of nerd-fonts: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/data/fonts/nerd-fonts/manifests/fonts.json
• Stylix configuration options: https://danth.github.io/stylix/
• nix-on-droid options: https://nix-community.github.io/nix-on-droid/nix-on-droid-options.html#sec-options

Very useful tools that are mostly not directly used in configuration but instead called on need:

• Convert non-NixOS machines to NixOS using nixos-infect
• Create various installation media with nixos-generators
• Remotely deploy NixOS using nixos-anywhere

And a few links that are not directly nix-related, but may still serve you well:

• List of pre-commit-hooks: https://devenv.sh/reference/options/#pre-commithooks