grain.yaml — Manifest Spec

The grain.yaml file at the root of a GRAIN repo is the machine-readable manifest that enables discovery, validation, and indexing on the FEAST site.

Validate with:

python bread-infra/scripts/validate_manifest.py grain.yaml

Schema: schemas/grain.schema.json (JSON Schema Draft 2020-12)
Template: templates/grain.yaml.template

Required fields

Field	Type	Description
`grain_schema_version`	string	Schema version. Must be `"1.0"`.
`id`	string	Repo name slug — lowercase, underscores → hyphens (e.g. `can-nano-shield`)
`name`	string	Human display name
`category`	enum	`shield` \| `card` \| `adapter` \| `module`
`status`	enum	`concept` \| `prototype` \| `released` \| `deprecated`
`summary`	string	One-line description (≤ 120 chars)
`license.hardware`	string	SPDX expression (e.g. `CERN-OHL-S-2.0`)
`repository.url`	string	HTTPS URL of the GitHub repo

Optional fields

Field	Type	Description
`version.hardware`	string \| null	Hardware version string
`compatibility`	list[string] \| null	What this grain connects to or is designed for
`related_slices`	list[string] \| null	Slice repo names this grain works with (e.g. `Slice_STPC`)
`hardware.form_factor`	string \| null	Physical form descriptor (e.g. `arduino-nano-shield`, `pcie-edge`)
`hardware.pcb_layers`	integer \| null	Number of copper layers
`firmware.language`	string \| null	Firmware language (e.g. `C++`) — omit section if no firmware
`firmware.framework`	string \| null	Firmware framework (e.g. `arduino`, `platformio`)
`license.firmware`	string \| null	SPDX expression for firmware license
`license.documentation`	string \| null	SPDX expression for documentation license
`metadata.tags`	list[string] \| null	Searchable tags
`metadata.updated`	string \| null	ISO 8601 date of last manifest update (e.g. `2026-06-12`)

Fields intentionally absent (vs slice.yaml)

The following fields from the Slice manifest are not present in grain.yaml because grains do not participate in the BREAD bus:

interfaces.host — no I2C address or bus role
capabilities — no ADPP capability model
protocol — no CRUMBS/ADPP
electrical.power_consumption — grains don’t sit on the BREAD bus power rail
hw_gen_current / hw_gen_supported — generation model is Slice-specific
compatibility.slice_spec / crumbs_protocol / anolis_provider_api

Example

grain_schema_version: "1.0"

id: "can-nano-shield"
name: "CAN Nano Shield"
status: "released"
category: "shield"
summary: "Arduino Nano-form-factor CAN bus shield for the FEAST ecosystem."

version:
  hardware: "1.0.0"

license:
  hardware: "CERN-OHL-S-2.0"
  firmware: "MIT"
  documentation: "CC-BY-SA-4.0"

repository:
  url: "https://github.com/feastorg/can-nano-shield"

compatibility:
  - "Arduino Nano"
  - "Arduino Nano Every"

related_slices: null

hardware:
  form_factor: "arduino-nano-shield"
  pcb_layers: 2

firmware:
  language: "C++"
  framework: "arduino"

metadata:
  tags: ["can", "shield", "nano"]
  updated: "2026-06-12"