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+++
date = '2026-02-14T10:30:00+01:00'
draft = false
title = 'Nix Flakes for Reproducible Builds'
summary = 'Notes on pinning tool versions with Nix flakes.'
+++

Nix flakes make it easy to pin exact versions of dependencies, like the Hugo
binary used to build this blog, so every contributor gets identical builds
without relying on a system-wide package manager.

## Pinning Hugo

The `flake.nix` in this repo pins an exact Hugo release through
`nixpkgs-multiverse`:

```nix
hugo = mv.version "hugo" "0.166.0";
```

Running `nix develop` drops that version onto `PATH`, and `nix build` uses
the same pin to produce the site.

{{% alert "tip" %}}
**Tip:** Pin the version once, in one file, and every machine that runs
`nix build` gets byte-identical output.
{{% /alert %}}