Dump a Unity scene hierarchy to a text file

using System.IO;
using System.Text;
using UnityEditor;
using UnityEngine;
using UnityEngine.SceneManagement;

/// <summary>
/// Dumps the open scene's hierarchy to a text file. Editor-only: put this in an
/// Editor/ folder. No Play mode, no runtime code in your build.
/// </summary>
public static class HierarchyDump
{
    [MenuItem("Tools/Dump Scene Hierarchy")]
    static void Dump()
    {
        Scene scene = SceneManager.GetActiveScene();

        var text = new StringBuilder();
        text.AppendLine(scene.name);

        GameObject[] roots = scene.GetRootGameObjects();
        for (int i = 0; i < roots.Length; i++)
        {
            Append(roots[i].transform, text, "", i == roots.Length - 1);
        }

        string path = EditorUtility.SaveFilePanel(
            "Dump scene hierarchy", "", $"{scene.name}-hierarchy", "txt");
        if (string.IsNullOrEmpty(path))
        {
            return;
        }

        File.WriteAllText(path, text.ToString());
        Debug.Log($"Wrote {roots.Length} roots to {path}");
    }

    static void Append(Transform transform, StringBuilder text, string prefix, bool isLast)
    {
        text.Append(prefix)
            .Append(isLast ? "└── " : "├── ")
            .AppendLine(transform.name);

        string childPrefix = prefix + (isLast ? "    " : "│   ");
        for (int i = 0; i < transform.childCount; i++)
        {
            Append(transform.GetChild(i), text, childPrefix, i == transform.childCount - 1);
        }
    }
}

Tools > Dump Scene Hierarchy. Editor-only — nothing here ships in your build.

static void AppendComponents(Transform transform, StringBuilder text)
{
    var names = new List<string>();

    foreach (Component component in transform.GetComponents<Component>())
    {
        // GetComponents returns a NULL entry for a MonoBehaviour whose script is
        // missing. Dereferencing it here is how a scene dump crashes on the one
        // scene you most wanted dumped.
        names.Add(component == null ? "<Missing Script>" : component.GetType().Name);
    }

    text.Append(" [").Append(string.Join(", ", names)).Append(']');
}

A missing MonoBehaviour script comes back as a null entry, not as a skipped one.

// Console: fine for one subtree, wrong for a whole scene. The Editor console
// stores and renders every entry, and a few thousand lines of text in a single
// entry is neither readable nor selectable.
Debug.Log(text.ToString());

// Clipboard: what you actually want when the destination is a bug report or a
// chat message. Works from any Editor script.
EditorGUIUtility.systemCopyBuffer = text.ToString();

// One subtree only — Debug.Log with a context object highlights the GameObject
// in the Hierarchy window when you click the log entry.
Debug.Log(SubtreeAsText(transform), transform.gameObject);

EditorGUIUtility.systemCopyBuffer is the one people miss, and it is usually the one they wanted.

// JsonUtility cannot do this, and the failure is quiet.
//
// Unity's serializer stops at a nesting depth of 7 and warns
// "Serialization depth limit 7 exceeded... There may be an object composition
// cycle", so a node type that holds a List<Node> of itself silently truncates
// at depth 7. A scene tree is exactly that shape.
//
// Write the JSON yourself. It is twenty lines, and it is the only version that
// is correct at depth 20.

static void AppendJson(Transform transform, StringBuilder text, string indent)
{
    text.Append(indent).Append("{\n");
    text.Append(indent).Append("  \"name\": ").Append(Quote(transform.name));

    if (transform.childCount > 0)
    {
        text.Append(",\n").Append(indent).Append("  \"children\": [\n");
        for (int i = 0; i < transform.childCount; i++)
        {
            AppendJson(transform.GetChild(i), text, indent + "    ");
            text.Append(i == transform.childCount - 1 ? "\n" : ",\n");
        }
        text.Append(indent).Append("  ]");
    }

    text.Append('\n').Append(indent).Append('}');
}

/// <summary>RFC 8259 string escaping. Object names contain quotes and backslashes.</summary>
static string Quote(string value)
{
    var quoted = new StringBuilder("\"");
    foreach (char c in value)
    {
        switch (c)
        {
            case '"':  quoted.Append("\\\""); break;
            case '\\': quoted.Append("\\\\"); break;
            case '\n': quoted.Append("\\n");  break;
            case '\r': quoted.Append("\\r");  break;
            case '\t': quoted.Append("\\t");  break;
            default:
                if (c < ' ')
                {
                    quoted.Append("\\u").Append(((int)c).ToString("x4"));
                }
                else
                {
                    quoted.Append(c);
                }
                break;
        }
    }
    return quoted.Append('"').ToString();
}

Twenty lines, correct at depth 20. The escaping is not optional — GameObject names contain quotes.