diff --git a/project.clj b/project.clj
index 3be2ba7..410d602 100644
--- a/project.clj
+++ b/project.clj
@@ -20,6 +20,7 @@
                  [sablono "0.3.6"]
                  [org.omcljs/om "0.9.0"]
                  [prismatic/om-tools "0.3.12"]
+                 [prismatic/schema "1.1.3"]
                  [com.cognitect/transit-cljs "0.8.239"]
                  [cljsjs/vega "2.6.0-0"]
                  [cljsjs/vega-lite "1.2.0-0"]
diff --git a/src/clj/vizard/lite.clj b/src/clj/vizard/lite.clj
index b97d55a..b7f18a6 100644
--- a/src/clj/vizard/lite.clj
+++ b/src/clj/vizard/lite.clj
@@ -1,8 +1,10 @@
 (ns vizard.lite
-  (:require [vizard.colors :refer [brews]]))
+  (:require [vizard.colors :refer [brews]]
+            [schema.core :as s]
+            [vizard.schema :refer [Vega]]))
 
 (defn colors [name]
   (get brews name name))
 
 (defn lite [vl-spec data-vals]
-  (assoc-in vl-spec [:data :values] data-vals))
+  (assoc-in (s/validate Vega vl-spec) [:data :values] data-vals))
diff --git a/src/clj/vizard/schema.clj b/src/clj/vizard/schema.clj
new file mode 100644
index 0000000..d78d08e
--- /dev/null
+++ b/src/clj/vizard/schema.clj
@@ -0,0 +1,610 @@
+(ns vizard.schema
+  "Schema for Vega-Lite specs. Translated from the JSON schema
+  https://vega.github.io/vega-lite/vega-lite-schema.json"
+  (:use [schema.core :exclude [atom fn defn defmethod letfn defrecord]]))
+
+(defn ranged [& {:keys [min max]}]
+ (cond
+   (and min max) (constrained Num (fn [x] (<= min x max)))
+   min (constrained Num (fn [x] (<= min x)))
+   max (constrained Num (fn [x] (<= x max)))
+   :else Num))
+
+(defn process-schema [schema]
+  (if (map? schema)
+    (into {} (for [[k v] schema] [(if (keyword? k) (optional-key k) k) v]))
+    schema))
+
+(defmacro defschema*
+  "Like schema.core/defschema, but keyword map keys are optional by default."
+  [name body]
+  (list 'defschema name (process-schema body)))
+
+(defschema*
+ Formula
+ {(required-key :field) Str, (required-key :expr) Str})
+
+(defschema* Orient (enum "horizontal" "vertical"))
+
+(defschema*
+ NiceTime
+ (enum "second" "minute" "hour" "day" "week" "month" "year"))
+
+(defschema*
+ Interpolate
+ (enum
+  "linear"
+  "linear-closed"
+  "step"
+  "step-before"
+  "step-after"
+  "basis"
+  "basis-open"
+  "basis-closed"
+  "cardinal"
+  "cardinal-open"
+  "cardinal-closed"
+  "bundle"
+  "monotone"))
+
+(defschema* BandSize (enum "fit"))
+
+(defschema*
+ Mark
+ (enum
+  "area"
+  "bar"
+  "line"
+  "point"
+  "text"
+  "tick"
+  "rule"
+  "circle"
+  "square"
+  "errorBar"))
+
+(defschema*
+ AxisConfig
+ {:gridDash [Num],
+  :properties Any,
+  :labels Bool,
+  :titleFontSize Num,
+  :labelMaxLength (ranged :min 1),
+  :tickPadding Num,
+  :labelBaseline Str,
+  :gridOpacity Num,
+  :titleOffset Num,
+  :offset Num,
+  :tickWidth Num,
+  :tickLabelColor Str,
+  :grid Bool,
+  :tickSizeEnd (ranged :min 0),
+  :shortTimeLabels Bool,
+  :titleMaxLength (ranged :min 0),
+  :labelAngle Num,
+  :titleFont Str,
+  :tickSizeMinor (ranged :min 0),
+  :titleColor Str,
+  :tickLabelFontSize Num,
+  :tickSize (ranged :min 0),
+  :layer Str,
+  :gridWidth Num,
+  :subdivide Num,
+  :axisWidth Num,
+  :ticks (ranged :min 0),
+  :tickSizeMajor (ranged :min 0),
+  :characterWidth Num,
+  :labelAlign Str,
+  :gridColor Str,
+  :tickLabelFont Str,
+  :axisColor Str,
+  :titleFontWeight Str,
+  :tickColor Str})
+
+(defschema* AxisOrient (enum "top" "right" "left" "bottom"))
+
+(defschema* VerticalAlign (enum "top" "middle" "bottom"))
+
+(defschema* FontWeight (enum "normal" "bold"))
+
+(defschema* HorizontalAlign (enum "left" "right" "center"))
+
+(defschema*
+ ScaleType
+ (enum
+  "linear"
+  "log"
+  "pow"
+  "sqrt"
+  "quantile"
+  "quantize"
+  "ordinal"
+  "time"
+  "utc"))
+
+(defschema* SortOrder (enum "ascending" "descending" "none"))
+
+(defschema*
+ TimeUnit
+ (enum
+  "year"
+  "month"
+  "day"
+  "date"
+  "hours"
+  "minutes"
+  "seconds"
+  "milliseconds"
+  "yearmonth"
+  "yearmonthdate"
+  "yearmonthdatehours"
+  "yearmonthdatehoursminutes"
+  "yearmonthdatehoursminutesseconds"
+  "monthdate"
+  "hoursminutes"
+  "hoursminutesseconds"
+  "minutesseconds"
+  "secondsmilliseconds"
+  "quarter"
+  "yearquarter"
+  "quartermonth"
+  "yearquartermonth"))
+
+(defschema*
+ Bin
+ {:min Num,
+  :max Num,
+  :base Num,
+  :step Num,
+  :steps [Num],
+  :minstep Num,
+  :div [Num],
+  :maxbins (ranged :min 2)})
+
+(defschema*
+ Shape
+ (enum
+  "circle"
+  "square"
+  "cross"
+  "diamond"
+  "triangle-up"
+  "triangle-down"))
+
+(defschema*
+ ScaleConfig
+ {:useRawDomain Bool,
+  :fontSizeRange [Num],
+  :shapeRange (either [Str] Str),
+  :bandSize (cond-pre BandSize Num),
+  :tickSizeRange [Num],
+  :barSizeRange [Num],
+  :textBandWidth (ranged :min 0),
+  :nominalColorRange (either [Str] Str),
+  :round Bool,
+  :opacity [Num],
+  :padding Num,
+  :ruleSizeRange [Num],
+  :sequentialColorRange (either [Str] Str),
+  :pointSizeRange [Num]})
+
+(defschema* FacetScaleConfig {:round Bool, :padding Num})
+
+(defschema*
+ AggregateOp
+ (enum
+  "values"
+  "count"
+  "valid"
+  "missing"
+  "distinct"
+  "sum"
+  "mean"
+  "average"
+  "variance"
+  "variancep"
+  "stdev"
+  "stdevp"
+  "median"
+  "q1"
+  "q3"
+  "modeskew"
+  "min"
+  "max"
+  "argmin"
+  "argmax"))
+
+(defschema*
+ SortField
+ {(required-key :field) Str,
+  (required-key :op) AggregateOp,
+  :order SortOrder})
+
+(defschema* Type (enum "quantitative" "ordinal" "temporal" "nominal"))
+
+(defschema*
+ FieldDef
+ {:field Str,
+  :type Type,
+  :value (cond-pre Str Num Bool),
+  :timeUnit TimeUnit,
+  :bin (cond-pre Bin Bool),
+  :aggregate AggregateOp,
+  :title Str})
+
+(defschema* StackOffset (enum "zero" "center" "normalize" "none"))
+
+(defschema* FontStyle (enum "normal" "italic"))
+
+(defschema*
+ MarkConfig
+ {:baseline VerticalAlign,
+  :strokeOpacity (ranged :min 0 :max 1),
+  :format Str,
+  :align HorizontalAlign,
+  :stroke Str,
+  :applyColorToBackground Bool,
+  :dx Num,
+  :color Str,
+  :tension Num,
+  :barSize Num,
+  :fill Str,
+  :strokeDash [Num],
+  :dy Num,
+  :shortTimeLabels Bool,
+  :fillOpacity (ranged :min 0 :max 1),
+  :orient Orient,
+  :interpolate Interpolate,
+  :angle Num,
+  :strokeDashOffset Num,
+  :theta Num,
+  :radius Num,
+  :font Str,
+  :size Num,
+  :tickThickness Num,
+  :stacked StackOffset,
+  :tickSize Num,
+  :strokeWidth (ranged :min 0),
+  :opacity (ranged :min 0 :max 1),
+  :fontStyle FontStyle,
+  :fontWeight FontWeight,
+  :shape (cond-pre Shape Str),
+  :barThinSize Num,
+  :fontSize Num,
+  :ruleSize Num,
+  :filled Bool,
+  :lineSize Num,
+  :text Str})
+
+(defschema*
+ CellConfig
+ {:strokeOpacity Num,
+  :stroke Str,
+  :clip Bool,
+  :fill Str,
+  :strokeDash [Num],
+  :width Num,
+  :fillOpacity Num,
+  :strokeDashOffset Num,
+  :strokeWidth Num,
+  :height Num})
+
+(defschema*
+ LegendConfig
+ {:properties Any,
+  :symbolSize Num,
+  :titleFontSize Num,
+  :labelBaseline Str,
+  :gradientStrokeWidth Num,
+  :offset Num,
+  :shortTimeLabels Bool,
+  :labelOffset Num,
+  :gradientHeight Num,
+  :orient Str,
+  :gradientStrokeColor Str,
+  :labelColor Str,
+  :titleFont Str,
+  :symbolShape Str,
+  :titleColor Str,
+  :gradientWidth Num,
+  :padding Num,
+  :labelFont Str,
+  :labelAlign Str,
+  :labelFontSize Num,
+  :symbolColor Str,
+  :symbolStrokeWidth (ranged :min 0),
+  :titleFontWeight Str,
+  :margin Num})
+
+(defschema*
+ DateTime
+ {:quarter (ranged :min 1 :max 4),
+  :day (cond-pre Str Num),
+  :date (ranged :min 1 :max 31),
+  :month (cond-pre Str Num),
+  :seconds (ranged :min 0 :max 59),
+  :year Num,
+  :hours (ranged :min 0 :max 23),
+  :milliseconds (ranged :min 0 :max 999),
+  :minutes (ranged :min 0 :max 59)})
+
+(defschema*
+ EqualFilter
+ {:timeUnit TimeUnit,
+  (required-key :field) Str,
+  :equal (cond-pre DateTime Str Num Bool)})
+
+(defschema*
+ OneOfFilter
+ {:timeUnit TimeUnit,
+  (required-key :field) Str,
+  :oneOf [(cond-pre DateTime Str Num Bool)]})
+
+(defschema*
+ Axis
+  {:gridDash [Num],
+   :properties Any,
+   :labels Bool,
+   :titleFontSize Num,
+   :format Str,
+   :labelMaxLength (ranged :min 1),
+   :tickPadding Num,
+   :labelBaseline Str,
+   :gridOpacity Num,
+   :titleOffset Num,
+   :offset Num,
+   :tickWidth Num,
+   :tickLabelColor Str,
+   :grid Bool,
+   :tickSizeEnd (ranged :min 0),
+   :shortTimeLabels Bool,
+   :orient AxisOrient,
+   :titleMaxLength (ranged :min 0),
+   :title Str,
+   :labelAngle (ranged :min 0 :max 360),
+   :titleFont Str,
+   :tickSizeMinor (ranged :min 0),
+   :titleColor Str,
+   :tickLabelFontSize Num,
+   :tickSize (ranged :min 0),
+   :layer Str,
+   :gridWidth Num,
+   :values (either [Num] [DateTime]),
+   :subdivide Num,
+   :axisWidth Num,
+   :ticks (ranged :min 0),
+   :tickSizeMajor (ranged :min 0),
+   :characterWidth Num,
+   :labelAlign Str,
+   :gridColor Str,
+   :tickLabelFont Str,
+   :axisColor Str,
+   :titleFontWeight Str,
+   :tickColor Str})
+
+(defschema*
+ Scale
+ {:zero Bool,
+  :useRawDomain Bool,
+  :exponent Num,
+  :bandSize (cond-pre BandSize Num),
+  :type ScaleType,
+  :round Bool,
+  :padding Num,
+  :nice (cond-pre NiceTime Bool),
+  :domain (either [Str] [Num] [DateTime]),
+  :clamp Bool,
+  :range (either [Str] [Num] Str)})
+
+(defschema*
+ PositionChannelDef
+ {:scale Scale,
+  :value (cond-pre Str Num Bool),
+  :field Str,
+  :type Type,
+  :title Str,
+  :bin (cond-pre Bin Bool),
+  :timeUnit TimeUnit,
+  :aggregate AggregateOp,
+  :axis Axis,
+  :sort (cond-pre SortOrder SortField)})
+
+(defschema* Facet {:row PositionChannelDef, :column PositionChannelDef})
+
+(defschema*
+ RangeFilter
+ {:timeUnit TimeUnit,
+  (required-key :field) Str,
+  :range [(cond-pre DateTime Num)]})
+
+(defschema*
+ Transform
+ {:filter
+  (either
+   EqualFilter
+   RangeFilter
+   OneOfFilter
+   [(cond-pre EqualFilter RangeFilter OneOfFilter Str)]
+   Str),
+  :filterInvalid Bool,
+  :calculate [Formula]})
+
+(defschema*
+ Legend
+  {:properties Any,
+   :symbolSize Num,
+   :titleFontSize Num,
+   :format Str,
+   :labelBaseline Str,
+   :gradientStrokeWidth Num,
+   :offset Num,
+   :shortTimeLabels Bool,
+   :labelOffset Num,
+   :gradientHeight Num,
+   :orient Str,
+   :gradientStrokeColor Str,
+   :labelColor Str,
+   :title Str,
+   :titleFont Str,
+   :symbolShape Str,
+   :titleColor Str,
+   :gradientWidth Num,
+   :values (either [Str] [Num] [DateTime]),
+   :padding Num,
+   :labelFont Str,
+   :labelAlign Str,
+   :labelFontSize Num,
+   :symbolColor Str,
+   :symbolStrokeWidth (ranged :min 0),
+   :titleFontWeight Str,
+   :margin Num})
+
+(defschema*
+ ChannelDefWithLegend
+ {:scale Scale,
+  :value (cond-pre Str Num Bool),
+  :legend Legend,
+  :field Str,
+  :type Type,
+  :title Str,
+  :bin (cond-pre Bin Bool),
+  :timeUnit TimeUnit,
+  :aggregate AggregateOp,
+  :sort (cond-pre SortOrder SortField)})
+
+(defschema* AreaOverlay (enum "line" "linepoint" "none"))
+
+(defschema*
+ OverlayConfig
+ {:line Bool,
+  :area AreaOverlay,
+  :pointStyle MarkConfig,
+  :lineStyle MarkConfig})
+
+(defschema*
+ OrderChannelDef
+ {:sort SortOrder,
+  :field Str,
+  :type Type,
+  :value (cond-pre Str Num Bool),
+  :timeUnit TimeUnit,
+  :bin (cond-pre Bin Bool),
+  :aggregate AggregateOp,
+  :title Str})
+
+(defschema*
+ UnitEncoding
+ {:y PositionChannelDef,
+  :path (either OrderChannelDef [OrderChannelDef]),
+  :color ChannelDefWithLegend,
+  :size ChannelDefWithLegend,
+  :opacity ChannelDefWithLegend,
+  :label FieldDef,
+  :shape ChannelDefWithLegend,
+  :order (either OrderChannelDef [OrderChannelDef]),
+  :x PositionChannelDef,
+  :y2 FieldDef,
+  :x2 FieldDef,
+  :text FieldDef,
+  :detail (either FieldDef [FieldDef])})
+
+(defschema*
+ Encoding
+ {:y PositionChannelDef,
+  :path (either OrderChannelDef [OrderChannelDef]),
+  :color ChannelDefWithLegend,
+  :size ChannelDefWithLegend,
+  :column PositionChannelDef,
+  :opacity ChannelDefWithLegend,
+  :label FieldDef,
+  :shape ChannelDefWithLegend,
+  :order (either OrderChannelDef [OrderChannelDef]),
+  :x PositionChannelDef,
+  :y2 FieldDef,
+  :x2 FieldDef,
+  :row PositionChannelDef,
+  :text FieldDef,
+  :detail (either FieldDef [FieldDef])})
+
+(defschema* FacetGridConfig {:color Str, :opacity Num, :offset Num})
+
+(defschema*
+ FacetConfig
+ {:scale FacetScaleConfig,
+  :axis AxisConfig,
+  :grid FacetGridConfig,
+  :cell CellConfig})
+
+(defschema*
+ Config
+ {:scale ScaleConfig,
+  :mark MarkConfig,
+  :countTitle Str,
+  :facet FacetConfig,
+  :background Str,
+  :legend LegendConfig,
+  :numberFormat Str,
+  :overlay OverlayConfig,
+  :axis AxisConfig,
+  :viewport Num,
+  :cell CellConfig,
+  :timeFormat Str})
+
+(defschema* DataFormatType (enum "json" "csv" "tsv" "topojson"))
+
+(defschema*
+ DataFormat
+ {:type DataFormatType,
+  :parse Any,
+  :property Str,
+  :feature Str,
+  :mesh Str})
+
+(defschema* Data {:format DataFormat, :url Str, :values [Any]})
+
+(defschema*
+ ExtendedUnitSpec
+ {:description Str,
+  :encoding Encoding,
+  :transform Transform,
+  :config Config,
+  :name Str,
+  :width Num,
+  (required-key :mark) Mark,
+  :height Num,
+  :data Data})
+
+(defschema*
+ UnitSpec
+ {:description Str,
+  :encoding UnitEncoding,
+  :transform Transform,
+  :config Config,
+  :name Str,
+  :width Num,
+  (required-key :mark) Mark,
+  :height Num,
+  :data Data})
+
+(defschema*
+ LayerSpec
+ {:width Num,
+  :height Num,
+  :layers [UnitSpec],
+  :name Str,
+  :description Str,
+  :data Data,
+  :transform Transform,
+  :config Config})
+
+(defschema*
+ FacetSpec
+ {(required-key :facet) Facet,
+  :spec (cond-pre UnitSpec LayerSpec),
+  :name Str,
+  :description Str,
+  :data Data,
+  :transform Transform,
+  :config Config})
+
+(defschema* Vega (cond-pre ExtendedUnitSpec FacetSpec LayerSpec))
diff --git a/src/clj/vizard/server.clj b/src/clj/vizard/server.clj
index ce504f0..ba33aed 100644
--- a/src/clj/vizard/server.clj
+++ b/src/clj/vizard/server.clj
@@ -14,6 +14,8 @@
    [taoensso.sente.server-adapters.aleph :refer (get-sch-adapter)]
    [taoensso.sente.packers.transit :as sente-transit]
    [cheshire.core :as json]
+   [vizard.schema :refer [Vega]]
+   [schema.core :as s]
    [clojure.java.io :as io])
   (:gen-class))
 
@@ -74,7 +76,7 @@
         :body (json/generate-string @last-spec)})
   (POST "/vl-spec" req
         (debugf "POST /vl-spec got: %s" req)
-        (let [vl-spec (json/parse-string (slurp (:body req)))]
+        (let [vl-spec (json/parse-string (slurp (:body req)) true)]
           (reset! last-vl-spec vl-spec)
           (doseq [uid (:any @connected-uids)]
             (chsk-send! uid [:vizard/vl-spec vl-spec]))