Slim schema format

@idfkit/schemas does not ship the raw epJSON schemas. It ships a reduced form carrying everything needed to parse, write, and resolve references, with the documentation metadata removed. This page describes that form; see Content-addressed schemas for why it exists.

Keys are single letters. This file is parsed on every cold start, and in a browser that start is a page load.

Bundle layout

data/
  index.json.gz              versions, and the manifest file for each
  types.json.gz              every unique type definition, keyed by content hash
  manifest-26-1-0.json.gz    type name -> hash, for one version
  manifest-25-2-0.json.gz
  ...

index.json is BundleIndex: a versions array, oldest first, and a manifests record mapping version string to manifest file name. A manifest is a flat Record<typeName, hash>. types.json is a flat Record<hash, SlimType>, shared by every version.

Files are gzipped and inflated by the source. httpSource uses DecompressionStream so the payload stays around 1 MB regardless of whether the server sets Content-Encoding.

SlimType

One object type, e.g. Zone.

Key	Meaning
f	All field names in IDF positional order, from legacy_idd.fields
p	Field definitions, keyed by epJSON field name
r	Required field names
nref	Reference lists the object's name contributes to
nreq	1 when the name is required
s	1 when the object is a singleton, e.g. Version, Building
anon	1 when the object has no name field at all, e.g. GlobalGeometryRules
x	Extensible group definition, if the type has one
g	IDD group, e.g. Thermal Zones and Surfaces

f is the load-bearing one: IDF is positional, and this array is the only thing that says which slot a value belongs to.

SlimField

Key	Meaning
t	Storage class, see below
auto	1 when the field accepts Autosize or Autocalculate as well as a number
ol	Reference lists this field points into — it is a foreign key
ref	Reference lists this field contributes to — it is a key
e	Permitted values, for a choice field
d	Schema default, applied on write when the field is absent
min	Inclusive minimum
max	Inclusive maximum
xmin	Exclusive minimum
xmax	Exclusive maximum
u	SI units, e.g. m
rc	1 when the value is case-sensitive and must not be normalized

ol and ref together are what the reference graph is built from: ref says a name enters a list, ol says a field reads from one.

FieldKind

The t key. It records how a value must be formatted on the way back out, which JavaScript cannot recover on its own — 3 and 3.0 are the same number at runtime.

Value	Meaning
'a'	Alpha. Written verbatim.
'n'	Real. Written with a decimal point preserved.
'i'	Integer. Written without a decimal point.
'arr'	Extensible array wrapper.

SlimExtensible

The x key on a type that has repeating field groups.

Key	Meaning
key	epJSON key holding the array, e.g. vertices
fields	Field names inside each repeat group, in IDF order
p	Definitions for the inner fields, from the array's items

What is dropped

note, memo, ip-units, and field_info. That is documentation metadata, it is most of the weight, and it sits on the critical path of every parse. Tooling that renders EnergyPlus documentation should read the source schemas directly, or use idfkit-docs.

Reading a definition

import { localBundle } from '@idfkit/schemas/node';

const schema = await localBundle().load('26.1.0');

schema.resolve('ZONE'); // 'Zone' — IDF type names are case-insensitive
schema.get('Zone'); // the SlimType
schema.field('Zone', 'x_origin'); // { t: 'n', u: 'm', d: 0 }

Definitions are frozen and shared by identity across versions with the same content hash, so they must not be mutated.