> For the complete documentation index, see [llms.txt](https://developers.felt.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developers.felt.com/felt-style-language/style-definition-blocks/the-filters-block.md).

# The filters block

The filters block contains information on how the layer is being filtered before displaying. In order for a feature to be shown on the map it must evaluate the filter expression to `true`.

Filters are written using a JSON infix notation that looks like one of `[identifier, operator, operand]`, `true` or `false` .

* Valid identifiers are either a feature property or a nested expression.
* Valid operators are:
  * `"lt"` – Less than
  * `"gt"` – Greater than
  * `"le"` – Less than or equal to
  * `"ge"` – Greater than or equal to
  * `"eq"` – Equal to
  * `"ne"` – Not equal to
  * `"and"` – And, cast to boolean
  * `"or"` – Or, cast to boolean
  * `"cn"` – Contains the operand, cast to string
  * `"nc"` – Does not contain the operand, cast to string
  * `"in"` – Contained in the operand list
  * `"ni"` – Not contained in the operand list
  * `"is"` – Used to match against null values
  * `"isnt"` – Used to match against null values
* Operands are:
  * A numerical value, a string value, a boolean value
  * An array of numerical, string, or boolean values, a shorthand expanded to these patterns:
    * Input 1: `[id, "in", [element1, …, elementN]]`
    * Expansion 1: `id` is equal (`"eq"`) to one or more of the elements
    * Input 2: `[id, "ni", [element1, …, elementN]]`
    * Expansion 2: `id` is not equal (`"ne"`) to any of the elements
    * Not defined for operators other than `"in"` and `"ni"`
  * A nested expression
* In cases of type mismatch cast the identifier value to the operand’s type
  * Type casting applies element-wise to lists with `"in"` and `"ni"` operators

{% code title="Example of a filter block that filters out features with a value less than 50000 on the acres property" %}

```json
"filters": ["acres", "lt", 50000]
```

{% endcode %}

{% code title="Example of a more complex filter block" %}

```json
"filters": [["acres", "ge", 50000], "and", ["acres", "le", 70000]]
```

{% endcode %}

## Behavior notes

* **Case & diacritics:** `eq`, `ne`, `gt`, `ge`, `lt`, `le`, `cn`, and `nc` compare strings case-insensitively and diacritic-insensitively. `["status", "eq", "active"]` matches `"Active"` and `"ACTIVE"`.
* **`in` / `ni` are case-sensitive**, unlike the operators above, and do per-element type coercion (`["id", "in", [5]]` matches a string `"5"`). `in` with an empty array always returns false; `ni` with an empty array always returns true.
* **Null handling:** use `is` / `isnt` only for null/existence checks (with `null` as the value) — not for value equality. Most other operators yield null (and filter the feature out) when the column is missing or null.
* **Type coercion:** the left-hand value is cast to match the right-hand type, so `["score", "eq", 100]` matches whether the column stores `100` or `"100"`.

## Common patterns

There is no single "between" operator — combine two comparisons:

```json
"filters": [["temperature", "ge", 0], "and", ["temperature", "le", 100]]
```

Check that a value exists and is non-empty:

```json
"filters": [["name", "isnt", null], "and", ["name", "ne", ""]]
```

**Three or more conditions must be written as nested pairs, not a flat list:**

```jsonc
// WRONG: [a, "and", b, "and", c]
// RIGHT:
"filters": [["a", "eq", 1], "and", [["b", "eq", 2], "or", ["c", "eq", 3]]]
```


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