Compile errors

You sent a schema to POST /v1/schemas/validate or POST /v1/extractions and got back a code starting with E-. Each error tells you three things: a stable code you can look up below, a JSON pointer to the part of the schema at fault, and for expressions, where in the expression string the problem is. Rely on the code, not the message, which may change.

{
  "error": {
    "code": "invalid_request",
    "message": "The schema does not compile.",
    "details": [
      { "code": "E-ENUM-VALUE", "message": "\"cancelled\" is not a value of this enum", "pointer": "/relations/2/expr", "span": [10, 21] }
    ]
  }
}

Here pointer says the problem is in the expression of the third relation, and span is the [start, end) byte range inside that expression: characters 10 to 21 of status == 'cancelled' are 'cancelled', a label the enum doesn’t have.

Schema structure

Code	Meaning	Example
E-JSON-SYNTAX	Not valid JSON, or nested deeper than 64 levels.	{"hydra_schema":
E-JSON-DUPKEY	An object has the same key twice.	{"name": "a", "name": "b"}
E-JSON-NUMBER	A number is not representable.	"scale": 1.5
E-SCHEMA-VERSION	Unsupported hydra_schema.	"hydra_schema": "9.9"
E-SCHEMA-UNKNOWN-KEY	A key the schema language does not define.	"colour": "red"
E-SCHEMA-MISSING-KEY	A required key is absent.	a field without "type"
E-SCHEMA-TYPE	Wrong JSON type.	"nullable": "yes"
E-SCHEMA-VALUE	Right JSON type, value not allowed (including invalid patterns and keys on the wrong field type).	"scale": 40, "eom": "sometimes"
E-FIELD-DUP	Two fields share a name.	two fields named "a"
E-FIELD-NAME	A field name is malformed or reserved.	"name": "when"
E-REL-DUP	Two relations share an id.	two relations with "id": "r"
E-RANGE	A range bound does not fit the type, does not parse, or min > max.	{"min": 10, "max": 1}
E-LIMIT	An input limit is exceeded; see limits.

Expressions

Code	Meaning	Example
E-EXPR-SYNTAX	The expression does not parse.	startDate <
E-EXPR-FUNC	Unknown function.	foo(x)
E-EXPR-ARITY	Wrong number of arguments.	round(x)
E-EXPR-LITERAL	Malformed literal.	date'2027-13-45'
E-EXPR-DEPTH	Nested more than 64 levels.	200 nested parentheses
E-EXPR-LENGTH	Longer than 16 KiB.

Types and names

Code	Meaning	Example
E-NAME-UNKNOWN	Not a field name.	nope == 1
E-ARRAY-RELATION	An array field in a relation or applicable_when.	tags == 'a'
E-ENUM-VALUE	String is not one of the enum’s values.	status == 'bogus'
E-TYPE	Operand types do not fit the operator.	startDate < rate
E-CURRENCY	Money of different currencies combined or compared.	eur == usd
E-BASIS	Duration bases disagree, a literal does not fit its basis, or the wrong basis for a date or datetime.	calendarDur < daysDur
E-DIV-UNROUNDED	/ outside the first argument of round.	rate / 2 == x
E-ROUND-ARG	round scale is not a literal from 0 to 28, or an unknown mode.	round(x, 40)
E-WHEN-NESTED	when that is not outermost, or inside applicable_when.	not when(a, b)
E-REL-TYPE	A relation is not true/false.	startDate + duration
E-APPLICABLE-TYPE	applicable_when is not true/false.	startDate + duration
E-APPLICABLE-SELF	applicable_when mentions its own field.
E-APPLICABLE-CYCLE	applicable_when conditions refer to each other in a cycle.	a when b, b when a

Constant evaluation

Code	Meaning	Example
E-CONST	A constant part cannot be evaluated: division by zero, overflow, a date out of range.	rate == round(1 / 0, 2)
E-REL-FALSE	A relation can never be true.	1 == 2
W-REL-TRIVIAL	Warning: a relation is always true (or its when condition never is) and is dropped.	1 == 1

Limits

Input	Limit	Error
Schema JSON	1 MiB	E-LIMIT
Fields	32 per schema on the API	400 invalid_request
Relations	10,000	E-LIMIT
JSON nesting	64 levels	E-JSON-SYNTAX
Expression	16 KiB, 64 levels deep	E-EXPR-LENGTH, E-EXPR-DEPTH
Document	50,000 characters on the API	400 invalid_request
Registers per relation	255 (very large expressions)	E-LIMIT