YAML Reference

Fathom's YAML authoring surface has one JSON Schema per construct. Schemas are regenerated from fathom.models on every docs build.

Per-construct reference

Construct	Page
Template	Template
Rule	Rule
Module	Module
Function	Function
Fact	Fact

File-level keys

Each YAML file holds one kind of construct, named by its top-level key. Any other top-level key is a CompilationError at load (parse_*_file, Engine.reload_rules), an error from fathom validate, and an error from POST /v1/compile:

File	Allowed top-level keys
Template	templates
Module	modules, focus_order
Function	functions, hierarchies
Rule	ruleset, version, module, rules

A mapping key given twice anywhere in a file (two expression: keys in one condition, say) is invalid YAML to Fathom: every loader rejects it instead of keeping the last value. Overriding a key merged in with << is not a duplicate.

A file with none of these keys (only unknown keys, {}, or a focus_order with no modules) holds no construct: fathom compile, fathom validate and POST /v1/compile all refuse it. POST /v1/compile compiles a document through the same function as fathom compile, so the two accept and refuse the same files, function files included.

Downloads

Construct	Schema
Template	template.schema.json
Rule	rule.schema.json
Module	module.schema.json
Function	function.schema.json
Hierarchy	schemas/hierarchy.schema.json

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