> ## Documentation Index
> Fetch the complete documentation index at: https://test-8862363a-feat-vpn-integration-docs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom Dependencies

> Add project-specific tools to Tembo sandboxes with tembo.nix.

Add a `tembo.nix` file to your repository root when your project needs tools that are not pre-installed in the sandbox. Tembo automatically detects the file and runs commands inside your Nix dev shell.

## Prerequisites

* You have a repository connected to Tembo.
* You know which system packages or language toolchains your project needs.

## Create tembo.nix

Create `tembo.nix` in your repository root with a default dev shell. Tembo uses `devShells.x86_64-linux.default` in the sandbox.

```nix theme={null}
{
  description = "Tembo Cloud VM Dependencies";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in {
        devShells.default = pkgs.mkShell {
          packages = with pkgs; [
            go
            rustc
            cargo
            jdk
          ];
        };
      }
    );
}
```

After you commit the file, new Tembo sessions use the dev shell automatically. Agents can then run commands that depend on those packages, such as `go test`, `cargo test`, or Java build tools.

## Add packages

Add packages to the `packages` list. For example, this dev shell adds PostgreSQL client tools and `pkg-config` for projects that compile native dependencies:

```nix theme={null}
{
  description = "Tembo Cloud VM Dependencies";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in {
        devShells.default = pkgs.mkShell {
          packages = with pkgs; [
            postgresql
            pkg-config
            openssl
          ];
        };
      }
    );
}
```

## Configure the shell

Use `shellHook` when the sandbox needs environment variables for local commands:

```nix theme={null}
{
  description = "Tembo Cloud VM Dependencies";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in {
        devShells.default = pkgs.mkShell {
          packages = with pkgs; [
            nodejs_22
            pnpm
          ];

          shellHook = ''
            export NODE_ENV=development
          '';
        };
      }
    );
}
```

Keep secrets out of `tembo.nix`. Add secrets through your sandbox environment variables instead.

## Tips

* Keep `tembo.nix` focused on system packages and toolchains that your project needs.
* Commit the file so Tembo can load it in every new session.
* Use [snapshots](../snapshots) if installing dependencies still takes meaningful time at the start of each session.