schema.json

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "CF Conventions for Zarr",
  "description": "Schema for Climate and Forecast (CF) conventions in Zarr. CF attributes use their standard unprefixed names for backwards compatibility with existing CF-compliant datasets and libraries like cf-python and xarray.",
  "type": "object",
  "properties": {
    "zarr_format": {
      "type": "integer",
      "description": "Zarr format version"
    },
    "node_type": {
      "type": "string",
      "enum": ["array", "group"],
      "description": "Type of Zarr node"
    },
    "attributes": {
      "type": "object",
      "description": "Zarr attributes containing convention metadata and CF attributes (unprefixed for backwards compatibility)",
      "properties": {
        "zarr_conventions": {
          "type": "array",
          "description": "Array of convention metadata objects",
          "contains": {
            "$ref": "#/$defs/conventionMetadata"
          }
        }
      },
      "required": ["zarr_conventions"],
      "$ref": "#/$defs/cfAttributes"
    }
  },
  "required": ["zarr_format", "node_type", "attributes"],
  "additionalProperties": true,
  "$defs": {
    "conventionMetadata": {
      "type": "object",
      "description": "CF conventions metadata object for use in zarr_conventions array",
      "properties": {
        "schema_url": {
          "type": "string",
          "const": "https://raw.githubusercontent.com/zarr-conventions/CF/refs/tags/v1/schema.json",
          "description": "URL to the JSON Schema definition for this convention"
        },
        "spec_url": {
          "type": "string",
          "description": "URL to the CF conventions specification document"
        },
        "uuid": {
          "type": "string",
          "const": "77c308c7-4db2-4774-8b2d-aa37e9997db6",
          "description": "UUID that permanently identifies this convention"
        },
        "name": {
          "type": "string",
          "const": "CF",
          "description": "Human-readable name of the convention (no colon suffix indicates unprefixed attributes for backwards compatibility)"
        },
        "version": {
          "type": "string",
          "pattern": "^[0-9]+\\.[0-9]+$",
          "description": "CF conventions version (e.g., '1.11', '1.10')"
        },
        "description": {
          "type": "string",
          "const": "Climate and Forecast conventions for self-describing geospatial data",
          "description": "Brief description of the convention's purpose and usage"
        }
      },
      "anyOf": [
        { "required": ["schema_url"] },
        { "required": ["spec_url"] },
        { "required": ["uuid"] }
      ],
      "additionalProperties": false
    },
    "cfAttributes": {
      "type": "object",
      "description": "CF convention attributes. All attributes use standard CF names (unprefixed) for backwards compatibility with existing CF-compliant datasets.",
      "properties": {
        "zarr_conventions": true,
        "Conventions": {
          "type": "string",
          "description": "CF conventions version string (e.g., 'CF-1.11'). May include other conventions separated by spaces.",
          "pattern": "(^|\\s)CF-[0-9]+\\.[0-9]+"
        },
        "title": {
          "type": "string",
          "description": "A succinct description of what is in the dataset"
        },
        "institution": {
          "type": "string",
          "description": "Specifies where the original data was produced"
        },
        "source": {
          "type": "string",
          "description": "The method of production of the original data"
        },
        "history": {
          "type": "string",
          "description": "Provides an audit trail for modifications to the original data"
        },
        "references": {
          "type": "string",
          "description": "Published or web-based references that describe the data or methods"
        },
        "comment": {
          "type": "string",
          "description": "Miscellaneous information about the data or methods"
        },
        "standard_name": {
          "type": "string",
          "description": "A standard name from the CF Standard Name Table that identifies the quantity"
        },
        "long_name": {
          "type": "string",
          "description": "A descriptive name that indicates a variable's content"
        },
        "units": {
          "type": "string",
          "description": "Units of the variable's values, recognized by UDUNITS"
        },
        "calendar": {
          "type": "string",
          "description": "Calendar used for time coordinates",
          "enum": [
            "standard",
            "gregorian",
            "proleptic_gregorian",
            "noleap",
            "365_day",
            "all_leap",
            "366_day",
            "360_day",
            "julian",
            "none"
          ]
        },
        "axis": {
          "type": "string",
          "description": "Identifies the axis type (X, Y, Z, or T)",
          "enum": ["X", "Y", "Z", "T"]
        },
        "positive": {
          "type": "string",
          "description": "Direction of increasing vertical coordinate values",
          "enum": ["up", "down"]
        },
        "coordinates": {
          "type": "string",
          "description": "Space-separated list of auxiliary coordinate variable names"
        },
        "bounds": {
          "type": "string",
          "description": "Name of the boundary variable for this coordinate"
        },
        "cell_methods": {
          "type": "string",
          "description": "Describes the characteristic of a field representing a cell"
        },
        "cell_measures": {
          "type": "string",
          "description": "Identifies variables containing cell areas or volumes"
        },
        "grid_mapping": {
          "type": "string",
          "description": "Name of the grid mapping variable containing CRS information"
        },
        "ancillary_variables": {
          "type": "string",
          "description": "Space-separated list of ancillary data variable names"
        },
        "flag_values": {
          "type": "array",
          "description": "Array of flag values for categorical data",
          "items": {
            "type": ["integer", "number"]
          }
        },
        "flag_meanings": {
          "type": "string",
          "description": "Space-separated list of flag meaning strings"
        },
        "flag_masks": {
          "type": "array",
          "description": "Array of flag masks for bit-field data",
          "items": {
            "type": "integer"
          }
        },
        "valid_min": {
          "type": "number",
          "description": "Minimum valid value for the variable"
        },
        "valid_max": {
          "type": "number",
          "description": "Maximum valid value for the variable"
        },
        "valid_range": {
          "type": "array",
          "description": "Two-element array [valid_min, valid_max]",
          "minItems": 2,
          "maxItems": 2,
          "items": {
            "type": "number"
          }
        },
        "_FillValue": {
          "type": ["number", "string", "null"],
          "description": "Value used to indicate missing or undefined data"
        },
        "missing_value": {
          "type": ["number", "string", "null"],
          "description": "Deprecated alias for _FillValue"
        },
        "add_offset": {
          "type": "number",
          "description": "Offset to be added after scaling: value = scale_factor * packed + add_offset"
        },
        "scale_factor": {
          "type": "number",
          "description": "Scale factor for packed data: value = scale_factor * packed + add_offset"
        },
        "compress": {
          "type": "string",
          "description": "Name of the dimension to be uncompressed"
        },
        "formula_terms": {
          "type": "string",
          "description": "Identifies variables used in computing dimensionless vertical coordinates"
        },
        "standard_name_vocabulary": {
          "type": "string",
          "description": "Name of the controlled vocabulary for standard_name"
        },
        "grid_mapping_name": {
          "type": "string",
          "description": "Name of the grid mapping/projection method"
        },
        "crs_wkt": {
          "type": "string",
          "description": "Well-Known Text representation of the CRS (WKT2)"
        },
        "semi_major_axis": {
          "type": "number",
          "description": "Semi-major axis of the ellipsoid"
        },
        "semi_minor_axis": {
          "type": "number",
          "description": "Semi-minor axis of the ellipsoid"
        },
        "inverse_flattening": {
          "type": "number",
          "description": "Inverse flattening of the ellipsoid"
        },
        "earth_radius": {
          "type": "number",
          "description": "Radius of the Earth for spherical approximation"
        },
        "longitude_of_prime_meridian": {
          "type": "number",
          "description": "Longitude of the prime meridian"
        },
        "false_easting": {
          "type": "number",
          "description": "False easting parameter"
        },
        "false_northing": {
          "type": "number",
          "description": "False northing parameter"
        },
        "longitude_of_projection_origin": {
          "type": "number",
          "description": "Longitude of projection origin"
        },
        "latitude_of_projection_origin": {
          "type": "number",
          "description": "Latitude of projection origin"
        },
        "scale_factor_at_projection_origin": {
          "type": "number",
          "description": "Scale factor at projection origin"
        },
        "scale_factor_at_central_meridian": {
          "type": "number",
          "description": "Scale factor at central meridian"
        },
        "longitude_of_central_meridian": {
          "type": "number",
          "description": "Longitude of central meridian"
        },
        "straight_vertical_longitude_from_pole": {
          "type": "number",
          "description": "Straight vertical longitude from pole"
        },
        "standard_parallel": {
          "oneOf": [
            { "type": "number" },
            {
              "type": "array",
              "items": { "type": "number" },
              "minItems": 1,
              "maxItems": 2
            }
          ],
          "description": "Standard parallel(s) for the projection"
        }
      },
      "additionalProperties": true
    }
  }
}