> ## Documentation Index
> Fetch the complete documentation index at: https://docs.corti.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Code filtering

> Restrict which codes the model may predict, and how filter validation works

## Filter code prediction output

Use the optional `filter` field to restrict which codes the model may predict. The `include` and `exclude` objects take a list of conditions used to constrain prediction output:

* **`include`**: codes matching all of these conditions are eligible. Empty or omitted means every code in the system is eligible.
* **`exclude`**: codes matching all of these conditions are removed from the eligible set. Empty or omitted means nothing is removed.

The final prediction set is the include set minus the exclude set.

Each condition has the following fields:

| Parameter  | Description                                                                                   |
| ---------- | --------------------------------------------------------------------------------------------- |
| `property` | The attribute to filter on, for example `code` (matches the `code` field on predicted codes). |
| `op`       | Comparison operator, one of `=`, `is-a`, `descendent-of`, `exists`, `in`. Defaults to `=`.    |
| `value`    | Comparison value.                                                                             |

`op` supports:

| Operator        | Matches                                                                                                         |
| --------------- | --------------------------------------------------------------------------------------------------------------- |
| `=`             | The property equals `value`.                                                                                    |
| `is-a`          | The code itself or any of its descendants.                                                                      |
| `descendent-of` | A strict descendant of the code (excludes the code itself).                                                     |
| `exists`        | Whether the property is set. `value: true` matches when it has a value; `value: false` matches when it doesn't. |
| `in`            | The property's value is one of the values in `value`.                                                           |

<Tip>
  Conditions defined in `include`/`exclude` are AND-combined. To match alternatives, list them in one condition's `value` instead of adding separate conditions. Use `op: "in"` for exact values or `op: "is-a"` with multiple ancestor codes where supported.
</Tip>

## Examples

<Accordion title="ICD-10">
  Limit code predict results to type 2 diabetes mellitus (`E11`) and its descendants, but never the specific code for diabetes with hyperosmolarity (`E11.00`):

  ```json theme={null}
  "filter": {
    "include": [
      { "property": "code", "op": "is-a", "value": ["E11"] }
    ],
    "exclude": [
      { "property": "code", "op": "=", "value": "E11.00" }
    ]
  }
  ```
</Accordion>

<Accordion title="SNOMED-CT">
  Filter SNOMED-CT concepts by `semantic_tag`, the clinical category a concept belongs to:

  ```json theme={null}
  "filter": {
    "include": [
      { "property": "semantic_tag", "op": "in", "value": ["disorder", "finding"] }
    ]
  }
  ```

  See [SNOMED CT](/coding/snomed-ct#filter-by-attribute) for the full list of supported `semantic_tag` values.
</Accordion>

<Tip>
  Omit the `filter` field for open-ended prediction: the API will predict across the full coding system.
</Tip>

***

## Filter validation

Filter conditions are validated before prediction runs. A request is rejected with a 400 error if:

* `property` isn't a supported attribute for the coding system (`code`, or a system-specific attribute like `semantic_tag`).
* `value` doesn't match the type `op` expects — a string or list of strings for `is-a`/`descendent-of`, a boolean for `exists`, a list for `in`.
* `is-a` or `descendent-of` is used on a property other than `code`.
* A code referenced in a condition (directly, or as the ancestor in an `is-a`/`descendent-of` condition) doesn't exist in the coding system.

<Info>
  When requesting multiple coding systems, the same `filter` applies to all of them.

  If a condition doesn't apply to one of the requested systems (e.g., a `semantic_tag` condition when requesting both SNOMED-CT and CPT), then that system fails validation and the entire request is rejected.
</Info>

No prediction is attempted when validation fails. See [Errors](/api-reference/errors) for the general error response shape.

<Note>Please [contact us](mailto:help@corti.ai) if you need help configuring your requests or have questions about advanced usage.</Note>