> 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/errors.md). # Errors Felt validates a style before it applies it. Where the errors show up depends on how you set the style: * **In-app style editor**: errors appear as a banner, one message per line. * **REST API** ([`update_style`](/rest-api/styling-layers.md)): the request fails with `422`. The error has the title `Invalid style format` and the detail `The provided style is an invalid Felt Style Language document`. The individual validation messages are in that error's own `errors` array: ```json { "errors": [ { "title": "Invalid style format", "detail": "The provided style is an invalid Felt Style Language document", "source": { "pointer": "/style" }, "errors": [ "Visualization: Attribute 'lineCap' is not a supported value. Supported values are butt, round, square" ] } ] } ``` * **JS SDK**: `setLayerStyle` rejects with an `Error` whose message is the validation messages joined by newlines. * **Felt MCP server and AI tools**: the tool returns `Invalid FSL:` followed by the messages, separated by `;` . These tools also run [strict checks](#strict-validation-felt-mcp-server-and-ai-tools) that the editor, REST API and SDK don't run. In the messages below, `` is the property name you set (for example `strokeWidth`), and `` is the value you gave it. {% hint style="info" %} Most `paint` and `label` value checks run only for `categorical`, `numeric`, `heatmap`, `hillshade` and `h3` styles. For `simple` styles, Felt checks `version`, the `config`, `legend`, `attributes` and `popup` blocks, and the boolean and icon options in `paint` and `label`, but it doesn't check values like `color`, `strokeWidth` or `lineCap`. An invalid value in a `simple` style may be accepted and then fail to render. {% endhint %} ### Malformed style **Problem**: The style isn't valid JSON, or it's missing something Felt needs to read it. **Solution**: Check the JSON syntax, and make sure the style has a `version` (currently `"2.3.1"`). **Error messages:** * `The style must be a valid JSON object` (style editor) * `The style is missing some required properties` (style editor) * `Style must have 'version' attribute` (style editor) * `Style 'version' definition must be a string` * `Style 'version' value must be one of 1.0, 1.1, 1.2, 1.2.1, 1.2.2, 1.3, 1.3.1, 1.3.2, 2.0, 2.1, 2.1.1, 2.2, 2.3, 2.3.1` * `Visualization has an invalid type`. The `type` must be one of `simple`, `categorical`, `numeric`, `heatmap`, `hillshade` or `h3`. ### Unexpected value or type **Problem**: One of the values in the style has an unsupported value or an invalid type. **Solution**: Change the value to one the message lists, or to the type it names. See [the paint block](/felt-style-language/style-definition-blocks/the-paint-block.md) and [the label block](/felt-style-language/style-definition-blocks/the-label-block.md) for each property's accepted values. **Error messages:** * `Visualization: Attribute '' is not a number`. Applies to `strokeWidth`, `opacity`, `haloWidth`, `lineHeight`, `letterSpacing`, `maxLineChars`, `repeatDistance` and `offset`. * `Visualization: Attribute '' is not a string`. Applies to `color`, `strokeColor`, `highlightColor`, `highlightStrokeColor`, and the label `color`, `haloColor`, `fontStyle` and `textTransform`. * `Visualization: Attribute 'size' is not a number or string` * `Visualization: Attribute 'fontSize' is not a number or an object` * `Visualization: Attribute 'lineCap' is not a supported value. Supported values are butt, round, square` * `Visualization: Attribute 'lineJoin' is not a supported value. Supported values are bevel, round, miter` * `Visualization dashArray has to be an array with even length` * `Visualization: Attribute 'placement' contains a not supported value . Supported values are N, NE, E, SE, S, SW, W, NW, Center, auto`. This is the point-label form, where `placement` is an array or `"auto"`. * `Visualization: Attribute 'placement' is not a supported value. Supported values are Above, Center, Below, AboveCenter`. This is the line-label form, where `placement` is a single string. * `Visualization: Attribute 'justify' contains a not supported value . Supported values are auto, left, right, center` * `Visualization: Attribute 'iconOverlap' contains a not supported value . Supported values are never, always, cooperative` * ` '' must be of type `. For example, `Style 'isClickable' must be of type boolean` or `label 'padding' must be of type number`. Felt uses this message for the boolean options (`isClickable`, `isHoverable`, `renderAsLines`, `showAboveBasemap`, `antialiasing`), for `minZoom`, `maxZoom` and the label `padding`, and for the popup's `keyAttributes` (array), `titleAttribute` and `imageAttribute` (string). ### Zoom-based values **Problem**: An [interpolator](/felt-style-language/zoom-based-styling/interpolators.md) is incomplete, or a property that only takes fixed values was given a smooth interpolator. **Solution**: Give the interpolator its stops (and, for `step`, its first output value; for `exp`, its base). For `lineCap`, `lineJoin` and `dashArray`, use a `step` interpolator. **Error messages:** * `Visualization: Linear interpolator: Not enough stops defined` * `Visualization: Step interpolator: Missing output0` * `Visualization: Step interpolator: Not enough stops defined` * `Visualization: Exp interpolator: Missing base value` * `Visualization: Exp interpolator: Not enough stops defined` * `Visualization: Attribute '' only supports step interpolators` * `Some of the step values are not a supported value. Supported values are ` * `Some of the step values are not a supported value. Only two-number array values are supported`. This applies to `dashArray`. ### The config block **Problem**: A value in [the config block](/felt-style-language/style-definition-blocks/the-config-block.md) isn't one Felt supports. **Solution**: Use one of the values the message lists. **Error messages:** * `Visualization 'labelAttribute' has to be a string` * `Visualization: All values in 'labelAttribute' must be a string` * `Visualization: Attribute 'aggregation' contains a not supported value . Supported values are count, sum, min, max, mean` * `Visualization: Attribute 'binMode' contains a not supported value . Supported values are fixed, low, medium, high`. `"auto"` is also accepted, although the message doesn't list it. ### Categorical visualization not working **Problem**: The style defines a [categorical visualization](/felt-style-language/types-of-visualizations/categorical-visualizations.md), but `categories` or `otherOrder` is set incorrectly. **Solution**: Set `categories` to an array of values or to a `top`, `bottom` or `all` shortcut, and set `otherOrder` to `"above"` or `"below"`. **Error messages:** * `Categories or showOther required`. The `categories` array is empty and `showOther` isn't set. * `Categories must be an array of strings, numbers or booleans` * `Categories type must be one of 'top', 'bottom' or 'all'` * `Categories type "" must have a count`. The `top` and `bottom` shortcuts need a `count`. * `'showOther' must be one of [above, below]`. Despite the wording, this message refers to the `otherOrder` field. `showOther` itself is a boolean, while `otherOrder` must be `"above"` or `"below"`. ### Numeric visualization not working **Problem**: The style defines a [numeric visualization](/felt-style-language/types-of-visualizations/numeric-visualizations-color-and-size.md), but `numericAttribute` or `steps` is set incorrectly. **Solution**: Set `numericAttribute` to a numeric column, and give `steps` at least two values or a valid [classification shortcut](/felt-style-language/classification-methods.md). **Error messages:** * `numericAttribute required` (style editor) * `steps must have at least 2 values` * `Steps type must be one of 'continuous', 'jenks', 'quantiles', 'equal-intervals', 'stddev' or 'geo-intervals'` * `Steps type "" must have a count`. Every shortcut except `continuous` needs a `count`. ### Raster visualization not working **Problem**: A [raster style](/felt-style-language/types-of-visualizations/raster.md) refers to a band that doesn't exist, or its band-math `method` is set incorrectly. **Solution**: Use band numbers that exist in the raster, starting at 1. Give `method` exactly one of `NDVI`, `NDMI` or `NDWI`, with numeric band indexes for the bands that method needs: `NIR` and `R` for NDVI, `NIR` and `SWIR` for NDMI, and `NIR` and `G` for NDWI. **Error messages:** * `Band out of bounds. Valid values are [1, ]` * `Method must be an object` * `Method must define a single raster algebra op` * `Method must be one of NDMI, NDVI, NDWI` * ` must be an object` * `Band is not supported. Must be one of G, NIR, R, SWIR` * `Band must be a number` * `"" band is required for ` * `outOfRangeValue must be one of 'color' or 'hide` * `Raster algebra visualizations only support continuous and equal-intervals steps types` * `Invalid color inteprolation method. Valid values are "rgb", "hcl"` * `Visualization: Attribute 'rasterResampling' is not a supported value. Supported values are nearest, linear` * `rasterResampling property is not supported for categorical rasters` ### Hillshade visualization not working **Problem**: A [hillshade](/felt-style-language/types-of-visualizations/raster.md#hillshade) value is out of range. **Solution**: Set `source` (the light direction) between 0 and 359, and `intensity` between 0 and 1. **Error messages:** * `Visualization: Attribute 'source' should be a number between 0 and 359` * `Visualization: Attribute 'intensity' should be a number between 0 and 1` ### Legend, attributes and popup blocks **Problem**: A value in [the legend](/felt-style-language/legends.md), [attributes](/felt-style-language/style-definition-blocks/the-attributes-block.md) or [popup](/felt-style-language/style-definition-blocks/the-popup-block.md) block has the wrong shape. **Solution**: Use the shape the message names. **Error messages:** * `Legend "displayName" can only be "auto" or an object` * `Legend "displayName" can only be "auto" when "steps" or "categories" are set` * `Attribute "" format must be an object` * `Attribute "" format must be a valid Numbro format` * `Popup 'popupLayout' must be of type string` * `Popup 'popupLayout' must be 'table' or 'list'` ### Strict validation (Felt MCP server and AI tools) **Problem**: The Felt MCP server's style tools and Felt's AI tools reject keys and filters that the editor, REST API and SDK accept without complaint. For example, a misspelled key such as `strokewidth` is ignored by the REST API but rejected here. **Solution**: Remove or correct the key, palette variable or filter that the message names. See [the filters block](/felt-style-language/style-definition-blocks/the-filters-block.md) for filter syntax. **Error messages:** * `Unknown key "". Valid top-level keys are: version, type, config, paint, label, legend, popup, attributes, filters` * `Unknown key "" in `. The block is `config`, `paint`, `label`, `legend` or `popup`. * `Unknown key "" in attributes[""]. Valid keys are: displayName, format` * `Unknown palette variable: `. A `color` or `strokeColor` refers to an `@` palette that doesn't exist. * `Filter: compound filters must be nested pairs, not a flat list. Use [a, "and", [b, "and", c]] instead of [a, "and", b, "and", c]. Got ` * `Filter: expected exactly 3 elements ([column, operator, value] or [expr, "and"|"or", expr]), got : ` * `Filter: unknown operator/logic gate "". Valid operators are: lt, gt, le, ge, eq, ne, cn, nc, in, ni, is, isnt. Valid logic gates are: and, or. Got ` * `Filter: operator "" requires an array value (or null), got `. This applies to `in` and `ni`. * `Filter: operator "" only checks for null/existence and requires a null value. To compare against a value, use "eq"/"ne" instead. Got `. This applies to `is` and `isnt`. * `Filter: operator "" requires a string, number, boolean, or null value, got ` * `Filter: attribute (first element) must be a string column name or null, got ` * `Filter: expected a [column, operator, value] expression, a [expr, "and"|"or", expr] compound, or null/true/false, got ` `` is empty for the top-level filter, and locates the nested expression otherwise, for example `[0][2]`. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. 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