diff --git a/Taskfile.yml b/Taskfile.yml
index f30744a..2a7949e 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -31,6 +31,7 @@ tasks:
                     --verbose \
                     --data \
                     -c ajv-keywords \
+                    -c ./src/sumOf.cjs \
                     -r schemas-json/classes.json \
                     -s schemas-json/character.json \
                     -d {{.CLI_ARGS}}
diff --git a/package.json b/package.json
index 85d65d1..5b02570 100644
--- a/package.json
+++ b/package.json
@@ -21,6 +21,8 @@
   "dependencies": {
     "ajv": "^8.11.0",
     "ajv-cli": "^5.0.0",
-    "ajv-keywords": "^5.1.0"
+    "ajv-keywords": "^5.1.0",
+    "json-pointer": "^0.6.2",
+    "lodash": "^4.17.21"
   }
 }
diff --git a/schemas-json/character.json b/schemas-json/character.json
index 704ef04..f5ddad2 100644
--- a/schemas-json/character.json
+++ b/schemas-json/character.json
@@ -19,6 +19,11 @@
                "type" : "array"
             },
             "max" : {
+               "sumOf" : {
+                  "list" : {
+                     "$data" : "1/log"
+                  }
+               },
                "type" : "number"
             }
          },
diff --git a/schemas-yaml/character.yml b/schemas-yaml/character.yml
index 3abe8ed..92e268e 100644
--- a/schemas-yaml/character.yml
+++ b/schemas-yaml/character.yml
@@ -3,30 +3,30 @@ title: Hyperboria character sheet
 type: object
 additionalProperties: false
 required:
-    - name
-    - player
-    - statistics
-    - class
-    - level
-    - health
+  - name
+  - player
+  - statistics
+  - class
+  - level
+  - health
 properties:
-    name: &string
-        type: string
-    player: *string
-    class: { $ref: '/classes.json' }
-    statistics:
-      type: object
-      allRequired: true
-      properties:
-        strength: &stat
-          $ref: '#/$defs/statistic'
-        dexterity: *stat
-        constitution: *stat
-        intelligence: *stat
-        wisdom: *stat
-        charisma: *stat
-    level: { type: number, minimum: 1 }
-    health: { $ref: '#/$defs/health' }
+  name: &string
+    type: string
+  player: *string
+  class: { $ref: "/classes.json" }
+  statistics:
+    type: object
+    allRequired: true
+    properties:
+      strength: &stat
+        $ref: "#/$defs/statistic"
+      dexterity: *stat
+      constitution: *stat
+      intelligence: *stat
+      wisdom: *stat
+      charisma: *stat
+  level: { type: number, minimum: 1 }
+  health: { $ref: "#/$defs/health" }
 $defs:
   statistic:
     type: number
@@ -34,14 +34,15 @@ $defs:
     maximum: 20
   health:
     type: object
-    required: [ max ]
+    required: [max]
     properties:
-        max: { type: number }
-        current: { type: number }
-        log:
-            type: array
-            description: history of health rolls
-            items: { type: number }
-            minItems: { $data: /level }
-            maxItems: { $data: /level }
-
+      max:
+        type: number
+        sumOf: { list: { $data: 1/log } }
+      current: { type: number }
+      log:
+        type: array
+        description: history of health rolls
+        items: { type: number }
+        minItems: { $data: /level }
+        maxItems: { $data: /level }
diff --git a/src/sumOf.cjs b/src/sumOf.cjs
new file mode 100644
index 0000000..2605de0
--- /dev/null
+++ b/src/sumOf.cjs
@@ -0,0 +1,47 @@
+const _ = require("lodash");
+const ptr = require("json-pointer");
+
+function resolvePointer(data, rootPath, relativePath) {
+    if (relativePath[0] === "/") return ptr.get(data, relativePath);
+
+    const m = relativePath.match(/^(\d+)(.*)/);
+    relativePath = m[2];
+    for (let i = 0; i < parseInt(m[1]); i++) {
+        rootPath = rootPath.replace(/\/[^\/]+$/, "");
+    }
+
+    return ptr.get(data, rootPath + relativePath);
+}
+
+module.exports = (ajv) =>
+    ajv.addKeyword({
+        keyword: "sumOf",
+        validate: function validate(
+            { list, map },
+            total,
+            _parent,
+            { rootData, instancePath }
+        ) {
+            if (list.$data) {
+                list = resolvePointer(rootData, instancePath, list.$data);
+            }
+
+            if (map) data = _.map(data, map);
+
+            if (_.sum(list) === total) return true;
+
+            validate.errors = [
+                {
+                    keyword: "sumOf",
+                    message: "should add up to sum total",
+                    params: {
+                        list,
+                    },
+                },
+            ];
+
+            return false;
+        },
+        $data: true,
+        errors: true,
+    });