> For the complete documentation index, see [llms.txt](https://docs.internetobject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.internetobject.org/parsing-and-errors/error-model.md).

# Error Model

Internet Object defines two classes of error. Each reported error carries a stable **error code** (a hyphenated identifier), a human-readable message, and the **position** in the source where it occurred.

## Syntax errors

Raised while tokenizing or parsing, before any schema is applied. They describe malformed *text*. Representative codes:

| Code                           | Condition                                                          |
| ------------------------------ | ------------------------------------------------------------------ |
| `expecting-bracket`            | a `{`, `}`, `[`, or `]` is missing                                 |
| `unexpected-token`             | a token appears where the grammar does not allow it                |
| `unexpected-positional-member` | a positional value follows a keyed one in an object                |
| `unknown-member`               | a MemberDef uses an option the declared type does not define       |
| `string-not-closed`            | a quoted string has no closing quote                               |
| `value-required`               | a value was expected (e.g. a key with no value) but none was found |
| `invalid-datetime`             | a date/time literal is malformed                                   |

> A conformant parser SHOULD report a malformed **numeric** literal (such as `0o89` or `0xGH`) as a coded syntax error. The reference implementation currently raises an uncoded internal error for some of these — a known gap.

## Validation errors

Raised while validating data against a schema. They describe values that do not satisfy the schema. Representative codes:

| Code                                  | Condition                                           |
| ------------------------------------- | --------------------------------------------------- |
| `invalid-type`                        | value is not of the declared type                   |
| `not-a-bool` / `not-a-string`         | value is not a boolean / string for that field      |
| `invalid-range`                       | number/date outside `min`/`max`                     |
| `out-of-range` / `invalid-length`     | array/string length outside `minLen`/`maxLen`/`len` |
| `invalid-min-length`                  | string/array shorter than the minimum               |
| `invalid-choice`                      | value is not one of `choices`                       |
| `invalid-pattern`                     | string does not match `pattern`                     |
| `invalid-email` / `invalid-url`       | malformed email/URL                                 |
| `invalid-scale` / `invalid-precision` | decimal scale/precision violated                    |
| `value-required`                      | a required field is missing                         |
| `null-not-allowed`                    | `null` given for a non-nullable field               |
| `additional-values-not-allowed`       | extra values without an open (`*`) schema           |

> Error **codes are stable**; messages and exact positions may vary between implementation versions. Tooling should branch on the code, not the message.

## Definition errors

A third small group arises from header references: `schema-not-defined`, `variable-not-defined` (see [Error Handling in Definitions](/definitions/error-handling.md)).

## See Also

* [Parser Behavior & Recovery](/parsing-and-errors/parser-behavior.md) · [Error Accumulation](/parsing-and-errors/error-accumulation.md)
* [Conformance Requirements](/conformance/requirements.md)


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