# Build your own Claude Code | Build Failure on NIXOS

**URL:** https://forum.codecrafters.io/t/build-your-own-claude-code-build-failure-on-nixos/15990
**Category:** Challenges
**Tags:** challenge:claude-code
**Created:** [March 17, 2026, 3:31pm UTC](https://forum.codecrafters.io/t/build-your-own-claude-code-build-failure-on-nixos/15990 "2026-03-17T15:31:11Z")
**Posts on this page:** 4
**Page:** 1

<div class="post-metadata">

### Author: ![devnchill](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/devnchill/32/7291_2.png) [@devnchill](https://forum.codecrafters.io/u/devnchill)
#### Post date: [March 17, 2026, 3:31pm UTC](https://forum.codecrafters.io/t/build-your-own-claude-code-build-failure-on-nixos/15990/1 "2026-03-17T15:31:11Z")

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I’m stuck on Stage #YY2 .

I am on nixos . I am using `devshell` to install python and uv . then point uv to use this python. I installed `codecrafters-cli` from `nixpkg`. Issue is when i am trying to run `codecrafters submit` , I get below error

Here are my logs:

```auto
codecrafters-claude-code-python on  master is 📦 v0.1.0 via 🐍 v3.14.3 (codecrafters-claude-code-python) via ❄️ impure (nix-shell-env) took 28s 
λ codecrafters submit
Submitting changes (commit: 52b29e2)...

We're warming up test runners for your repository, please bear with us.
Subsequent builds will be snappy ⚡

Streaming build logs...

[build] Starting build...
[build] If you don't see logs for 60s+, please contact us at hello@codecrafters.io
[build] Step 1 complete.
[build] Step 2 complete.
[build] Step 3 complete.
[build] Step 4 complete.
[build] Step 5 complete.
[build] Step 6 complete.
[build] Step 7 complete.
[build] Step 8 complete.
[build] Step 9 complete.
[build] Step 10 complete.
[build] Step 11 complete.
[build] Step 12 complete.
[build] Step 13 complete.
[build] Step 14 complete.
[build] Error: failed to calculate checksum of ref wue8mn02yfmm39qrqsae76xl4::02c3u3nour5g7oyxp4hswntdl: "/nix/store/a453sxdh5yk3g457ds1ph3v6xf6d728g-source": not found.
[build] Build failed. Check the logs above for the reason.
[build] If you think this is a CodeCrafters error, please contact us at hello@codecrafters.io.

Looks like your codebase failed to build.
If you think this is a CodeCrafters error, please let us know at
hello@codecrafters.io.

```

here is my devshell that i used to download python and uv

```nix
{
  description = "A very basic flake";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };

  outputs =
    { self, nixpkgs }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};
    in
    {
      devShells.${system}.default = pkgs.mkShell {

        packages = with pkgs; [
          codecrafters-cli
          nil
          nixfmt

          uv
          pyright
          ruff

          python314
        ];
        shellHook = ''
          					export UV_PYTHON_DOWNLOADS=never
                    				'';
      };
    };
}

```

I also have this in `pyproject.toml` to disable uv from managing python

```toml
[tools.uv]
python-downloads = "never"
python-preference = "only-system"

```

Any idea what could be the reason and how to fix it ?

---

<div class="post-metadata">

### Author: ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)
#### Post date: [March 17, 2026, 3:31pm UTC](https://forum.codecrafters.io/t/build-your-own-claude-code-build-failure-on-nixos/15990/2 "2026-03-17T15:31:12Z")

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Hi, thanks for your post!

I’m currently out of the office and will be back on March 23. I’ll get back to you as soon as possible once I return.

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<div class="post-metadata">

### Author: ![devnchill](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/devnchill/32/7291_2.png) [@devnchill](https://forum.codecrafters.io/u/devnchill)
#### Post date: [March 17, 2026, 4:54pm UTC](https://forum.codecrafters.io/t/build-your-own-claude-code-build-failure-on-nixos/15990/3 "2026-03-17T16:54:29Z")

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Solved it. I bymistake commited the .direnv

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<div class="post-metadata">

### Author: ![system](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/3X/7/0/700657133935c15703e22c7c8870394f6e6dc27d.svg) [@system](https://forum.codecrafters.io/u/system)
#### Post date: [March 22, 2026, 4:55pm UTC](https://forum.codecrafters.io/t/build-your-own-claude-code-build-failure-on-nixos/15990/4 "2026-03-22T16:55:15Z")

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