target.json Reference

The target.json file is used to describe yotta targets. It defines where to find the CMake toolchain used to control compilation, and the data that can be used by modules to include different dependencies or compile different code when building for different targets.

Example File

  "name": "frdm-k64f-gcc",
  "version": "0.0.7",
  "license": "Apache-2.0",
  "inherits": {
    "mbed-gcc": "~0.1.2"
        "baz": 123,
        "frequency": 11
  "toolchain": "CMake/toolchain.cmake",
  "cmakeIncludes": [
  "scripts": {
    "debug": ["valinor", "--target", "K64F", "$program" ],
    "test": [ "mbed_test_wrapper", "--target", "K64F", "$program" ]
  "similarTo": [


name required

type: String

The unique name of the target. Globally unique. As the target also defines which compiler is used to build, target names should normally explicitly state which compiler they use (e.g. some-target-gcc, some-target-armcc).

Names can use only lowercase letters, numbers, and hyphens, but must start with a letter. (This reduces problems with case insensitive filesystems, and confusingly similar names.)

# version required

type: String (conforming to the semver specification)

yotta uses Semantic Versions for targets and modules. See the module.json reference for details.

# inherits

type: hash of target-name to version-specification

A target descriptions may inherit from a more generic target description. This allows target descriptions for similar hardware devices to share a common base implementation, overriding only the parts that need to be different.

Only a single base target may be specified for any target.


  "inherits": {
    "mbed-gcc": "~0.1.2"

# similarTo

type: Array of String

An array of target identifiers that this target is similar to. This list is used when resolving target-specific dependencies.

When calculating the dependencies to install, yotta uses the first section from targetDependencies that matches one of the identifiers in this list.

The identifiers are arbitrary strings, and do not need to be the names of other targets.

# licenses deprecated

See also: license. The licenses property was formerly a method of specifying that multiple licenses applied to a target. It’s now preferred to use a single license field containing a SPDX license expression.

licenses example:

  "licenses": [
      "url": "",
      "type": "Apache-2.0"

# license required

type: String "<SPDX license identifier>"**

The license property in target.json should include all of the licenses that affect code in your target. For example:

  "license": "Apache-2.0"

The license identifiers are from the SPDX list. SPDX license expressions can be used for compound licenses.

According to SPDX v2.0, custom licenses in a file should be entered as:

  "license": "LicenseRef-LICENSE.pdf"

# description

type: String

Brief description of what this target is for. This helps other people to find your target. Include a file with a longer description, and preferably a photo of the target platform.

# keywords

type: Array of String

Keywords describe what this target is for, and help other people to find it. For example, a target to build for a specific mbed board should be tagged with mbed-target:{mbedtargetname} (where {mbedtargetname} should be replaced with the mbed target name of the development board.

# toolchain

type: String (path relative to target root directory)

Path to the target’s CMake toolchain file. If this target inherits from another target that provides a functioning toolchain this property is optional.

# cmakeIncludes

type: Array of String (paths relative to target root directory)

List of CMake files which should be included in every module built. These can be used to modify the rules for building libraries/executables as necessary. For example, a target description might provide the ability to produce selected code-coverage information by appending code-coverage flags when compiling some selected subset of modules.

The name of the library being built by the current module is available in the included cmake files as YOTTA_MODULE_NAME.

# scripts

type: hash of script-name to command

Each command is either an array of the separate command arguments, or a single string which yotta will split into parts based on normal shell command splitting rules.

In all cases any instances of $program in the command text will be replaced with the path to yotta-compiled program about to be launched/debugged. The path to the program is also available to commands as the YOTTA_PROGRAM environment variable.

Any script which is a .py file will be invoked using the python interpreter which is running yotta.

The supported scripts are:

  • debug: this is the command that’s run by yotta debug, it should probably open a debugger.
  • test: this command is used by yotta test to run each test. For cross-compiling targets, this command should load the binary on to the target device, and then print the program’s output on standard out.
  • start: this command is used by yotta start to start an executable. For cross-compiling targets, this command should load the binary onto the target device, and launch it.
  • preVersion: Runs before the yotta version command increments the version number. The old and new version numbers are available as environment variables YOTTA_OLD_VERSION and YOTTA_NEW_VERSION. Can return non-zero to prevent continuing.
  • postVersion: Runs after the version has been bumped by yotta version, but before any changes have been committed or tagged in VCS (returning non-zero will prevent anything from being committed).
  • prePublish: Runs before the target is published. Can return non-zero to prevent publishing.
  • postPublish: Runs after the target has been published. Tweet here.
  • postInstall: Runs once after a target is downloaded into yotta_targets.


To use lldb as the debugger, a target for native compilation would define:

   "scripts": {
      "debug": ["lldb", "$program"],

# config

type: hash of config data

Optional config data to define or override. For details on the yotta config system, see the config reference.

debugServer deprecated: use scripts.debug instead

type: Array of String (command parts)

Optional command to run a debug server.

debug deprecated: use scripts.debug instead

type: Array of String (command parts)

Optional command to run when the yotta debug is invoked.

Use $program for the name of the program that’s being debugged, for example:

  "debug": [
    "gdb", "$program", "--eval", "target remote localhost:2331"


type: version specification

A version specification for the version of yotta that this target requires. For example:

   "yotta": ">=0.13.0"
   "yotta": ">=0.10.0, !0.12.0"

If your target requires functionality that was introduced in a specific yotta version, then you can use this property so that older versions of yotta report a clear error message to the user that they need to upgrade before using your target.