Tiled is a great tool to design levels and maps. From Tiled’s documentation:

Tiled is a 2D level editor that helps you develop the content of your game. Its primary feature is to edit tile maps of various forms, but it also supports free image placement as well as powerful ways to annotate your level with extra information used by the game. Tiled focuses on general flexibility while trying to stay intuitive.

In terms of tile maps, it supports straight rectangular tile layers, but also projected isometric, staggered isometric and staggered hexagonal layers. A tileset can be either a single image containing many tiles, or it can be a collection of individual images. In order to support certain depth faking techniques, tiles and layers can be offset by a custom distance and their rendering order can be configured.

Tiled Editor

Flame provides a package (flame_tiled) that bundles a dart package which allows you to parse TMX (XML) files and access the tiles, objects, and everything in there.

The dart package provides a simple Tiled class and flame_tiled provides a component wrapper TiledComponent, for the map rendering, which renders the tiles on the screen and supports rotations and flips.

Tiled Editor

You can choose to download the Tiled map editor and create interactive maps that can be loaded into your game. At its core, the Tiled map editor creates a TMX file that can be parsed and used within your game.