All components of Flipper Zero firmware — services, user applications, and system settings — are developed independently. Each component has a build system manifest file named `application.fam`, which defines the basic properties of that component and its relations to other parts of the system.
When building firmware, `fbt` collects all app manifests and processes their dependencies. Then it builds only those components referenced in the current build configuration. See [FBT docs](fbt.md) for details on build configurations.
- **appid**: string, app ID within the build system. It is used to specify which app to include in the build configuration and resolve dependencies and conflicts.
- **entry_point**: C function to be used as the app's entry point. Note that C++ function names are mangled, so you need to wrap them in `extern "C"` to use them as entry points.
- **cdefines**: C preprocessor definitions to declare globally for other apps when the current app is included in the active build configuration. **For external apps**: specified definitions are used when building the app itself.
- **requires**: list of app IDs to include in the build configuration when the current app is referenced in the list of apps to build.
- **conflicts**: list of app IDs with which the current app conflicts. If any of them is found in the constructed app list, `fbt` will abort the firmware build process.
- **stack_size**: stack size in bytes to allocate for an app on its startup. Note that allocating a stack too small for an app to run will cause a system crash due to stack overflow, and allocating too much stack space will reduce usable heap memory size for apps to process data. _Note: you can use `top` and `free` CLI commands to profile your app's memory usage._
- **order**: order of an app within its group when sorting entries in it. The lower the order is, the closer to the start of the list the item is placed. _Used for ordering startup hooks and menu entries._
- **sdk_headers**: list of C header files from this app's code to include in API definitions for external apps.
- **targets**: list of strings and target names with which this app is compatible. If not specified, the app is built for all targets. The default value is `["all"]`.
- **resources**: name of a folder within the app's source folder to be used for packacking SD card resources for this app. They will only be used if app is included in build configuration. The default value is `""`, meaning no resources are packaged.
- **sources**: list of strings, file name masks used for gathering sources within the app folder. The default value of `["*.c*"]` includes C and C++ source files. Apps cannot use the `"lib"` folder for their own source code, as it is reserved for **fap_private_libs**. Paths starting with `"!"` are excluded from the list of sources. They can also include wildcard characters and directory names. For example, a value of `["*.c*", "!plugins"]` will include all C and C++ source files in the app folder except those in the `plugins` (and `lib`) folders. Paths with no wildcards (`*, ?`) are treated as full literal paths for both inclusion and exclusion.
- **fap_version**: string, app version. The default value is "0.1". You can also use a tuple of 2 numbers in the form of (x,y) to specify the version. It is also possible to add more dot-separated parts to the version, like patch number, but only major and minor version numbers are stored in the built .fap.
- **fap_libs**: list of extra libraries to link the app against. Provides access to extra functions that are not exported as a part of main firmware at the expense of increased `.fap` file size and RAM consumption.
- **fap_description**: string, may be empty. Short app description.
- **fap_author**: string, may be empty. App's author.
- **fap_weburl**: string, may be empty. App's homepage.
- **fap_icon_assets**: string. If present, it defines a folder name to be used for gathering image assets for this app. These images will be preprocessed and built alongside the app. See [FAP assets](AppsOnSDCard.md) for details.
- **fap_extbuild**: provides support for parts of app sources to be built by external tools. Contains a list of `ExtFile(path="file name", command="shell command")` definitions. `fbt` will run the specified command for each file in the list.
- **fal_embedded**: boolean, default `False`. Applies only to PLUGIN type. If `True`, the plugin will be embedded into host app's .fap file as a resource and extracted to `apps_assets/APPID` folder on its start. This allows plugins to be distributed as a part of the host app.
Note that commands are executed at the firmware root folder, and all intermediate files must be placed in an app's temporary build folder. For that, you can use pattern expansion by `fbt`: `${FAP_WORK_DIR}` will be replaced with the path to the app's temporary build folder, and `${FAP_SRC_DIR}` will be replaced with the path to the app's source folder. You can also use other variables defined internally by `fbt`.
- **fap_private_libs**: list of additional libraries distributed as sources alongside the app. These libraries will be built as a part of the app build process.
Library sources must be placed in a subfolder of the `lib` folder within the app's source folder.
- **name**: name of the library's folder. Required.
- **fap_include_paths**: list of the library's relative paths to add to the parent fap's include path list. The default value is `["."]`, meaning the library's source root.
- **sources**: list of filename masks to be used for gathering include files for this library. Paths are relative to the library's source root. The default value is `["*.c*"]`.
- **cflags**: list of additional compiler flags to be used for building this library. The default value is `[]`.
- **cdefines**: list of additional preprocessor definitions to be used for building this library. The default value is `[]`.
- **cincludes**: list of additional include paths to be used for building this library. Paths are relative to the app's root. This can be used for providing external search paths for this library's code — for configuration headers. The default value is `[]`.
For that snippet, `fbt` will build 2 libraries: one from sources in `lib/mbedtls` folder and another from sources in the `lib/loclass` folder. For the `mbedtls` library, `fbt` will add `lib/mbedtls/include` to the list of include paths for the app and compile only the files specified in the `sources` list. Additionally, `fbt` will enable `MBEDTLS_ERROR_C` preprocessor definition for `mbedtls` sources.
For the `loclass` library, `fbt` will add `lib/loclass` to the list of the included paths for the app and build all sources in that folder. Also, `fbt` will disable treating compiler warnings as errors for the `loclass` library, which can be useful when compiling large 3rd-party codebases.
