diff --git a/config/config.ts b/config/config.ts
index 6b0a060..bdfccd5 100644
--- a/config/config.ts
+++ b/config/config.ts
@@ -1,17 +1,18 @@
+import { ConfigSpec, ValueSpecAny } from "../types.ts";
 import { BuilderExtract, IBuilder } from "./builder.ts";
 import { Value } from "./value.ts";
 
-export class Config<A> extends IBuilder<A> {
+export class Config<A extends ConfigSpec> extends IBuilder<A> {
   static empty() {
     return new Config({});
   }
-  static withValue<K extends string, B>(key: K, value: Value<B>) {
+  static withValue<K extends string, B extends ValueSpecAny>(key: K, value: Value<B>) {
     return new Config({
       [key]: value.build(),
     } as { [key in K]: B });
   }
 
-  static of<B extends { [key: string]: Value<unknown> }>(spec: B) {
+  static of<B extends { [key: string]: Value<C> }, C extends ValueSpecAny>(spec: B) {
     // deno-lint-ignore no-explicit-any
     const answer: { [K in keyof B]: BuilderExtract<B[K]> } = {} as any;
     for (const key in spec) {
@@ -20,7 +21,7 @@ export class Config<A> extends IBuilder<A> {
     }
     return new Config(answer);
   }
-  addValue<K extends string, B>(key: K, value: Value<B>) {
+  addValue<K extends string, B extends ValueSpecAny>(key: K, value: Value<B>) {
     return new Config({
       ...this.a,
       [key]: value.build(),
diff --git a/config/list.ts b/config/list.ts
index 4971222..b54ec10 100644
--- a/config/list.ts
+++ b/config/list.ts
@@ -1,28 +1,32 @@
-import { UniqueBy } from "../types.ts";
+import { ConfigSpec, Tag, UniqueBy, ValueSpecList } from "../types.ts";
 import { BuilderExtract, IBuilder } from "./builder.ts";
 import { Config } from "./config.ts";
 import { Default, NullableDefault, NumberSpec, StringSpec } from "./value.ts";
 import { Description } from "./value.ts";
+import * as T from "../types.ts";
 
-export class List<A> extends IBuilder<A> {
+export class List<A extends Tag<"list", ValueSpecList>> extends IBuilder<A> {
   // deno-lint-ignore ban-types
   static boolean<A extends Description & Default<boolean[]> & { range: string; spec: {} }>(a: A) {
     return new List({
+      type: "list" as const,
       subtype: "boolean" as const,
       ...a,
     });
   }
 
   static string<
-    A extends Description & Default<string[] & { range: string; spec: null | { range: string; spec: StringSpec } }>
+    A extends Description & Default<string[]> & { range: string; spec: { range: string; spec: StringSpec } }
   >(a: A) {
     return new List({
+      type: "list" as const,
       subtype: "string" as const,
       ...a,
-    });
+    } as T.Tag<"list", T.Subtype<"string", T.WithDescription<T.WithDefault<T.ListSpec<T.ValueSpecString>, string[]>>>>);
   }
   static number<A extends Description & Default<number[]> & { range: string; spec: NumberSpec }>(a: A) {
     return new List({
+      type: "list" as const,
       subtype: "number" as const,
       ...a,
     });
@@ -40,6 +44,7 @@ export class List<A> extends IBuilder<A> {
       }
   >(a: A) {
     return new List({
+      type: "list" as const,
       subtype: "enum" as const,
       ...a,
     });
@@ -54,7 +59,7 @@ export class List<A> extends IBuilder<A> {
           "unique-by": null | UniqueBy;
         };
       },
-    B
+    B extends ConfigSpec
   >(a: A) {
     const { spec: previousSpec, ...rest } = a;
     const { spec: previousSpecSpec, ...restSpec } = previousSpec;
@@ -68,9 +73,10 @@ export class List<A> extends IBuilder<A> {
       ...rest,
     };
     return new List({
+      type: "list" as const,
       subtype: "object" as const,
       ...value,
-    });
+    } as T.Tag<"list", T.Subtype<"object", T.WithDescription<T.WithNullableDefault<T.ListSpec<T.ValueSpecObject>, Record<string, unknown>[]>>>>);
   }
   static union<
     A extends Description &
@@ -90,7 +96,8 @@ export class List<A> extends IBuilder<A> {
           "unique-by": null | UniqueBy | undefined;
         };
       },
-    Variants extends { [key: string]: Config<unknown> }
+    Variants extends { [key: string]: Config<ConfigSpec> },
+    B extends ConfigSpec
   >(a: A) {
     const { spec: previousSpec, ...rest } = a;
     const { variants: previousVariants, ...restSpec } = previousSpec;
@@ -109,6 +116,7 @@ export class List<A> extends IBuilder<A> {
       ...rest,
     };
     return new List({
+      type: "list" as const,
       subtype: "union" as const,
       ...value,
     });
diff --git a/config/pointer.ts b/config/pointer.ts
index 26ae61e..efd4ae2 100644
--- a/config/pointer.ts
+++ b/config/pointer.ts
@@ -1,7 +1,8 @@
+import { ValueSpecAny } from "../types.ts";
 import { IBuilder } from "./builder.ts";
 import { Description } from "./value.ts";
 
-export class Pointer<A> extends IBuilder<A> {
+export class Pointer<A extends ValueSpecAny> extends IBuilder<A> {
   static packageTorKey<A extends Description & { "package-id": string; interface: string }>(a: A) {
     return new Pointer({
       type: "pointer" as const,
diff --git a/config/value.ts b/config/value.ts
index c656a8d..95788dc 100644
--- a/config/value.ts
+++ b/config/value.ts
@@ -1,8 +1,16 @@
+import { ConfigSpec, Tag, ValueSpecAny, ValueSpecList } from "../types.ts";
+import * as T from "../types.ts";
 import { BuilderExtract, IBuilder } from "./builder.ts";
 import { Config } from "./config.ts";
 import { List } from "./list.ts";
 import { Pointer } from "./pointer.ts";
 
+export type DefaultString =
+  | string
+  | {
+      charset: string | null | undefined;
+      len: number;
+    };
 export type Description = {
   name: string;
   description: string | null;
@@ -12,7 +20,7 @@ export type Default<A> = {
   default: A;
 };
 export type NullableDefault<A> = {
-  default: A | null;
+  default?: A;
 };
 
 export type StringSpec = {
@@ -38,30 +46,29 @@ export type Nullable = {
 };
 
 type _UniqueBy =
-  | null
   | string
   | {
-      any: string;
+      any: _UniqueBy[];
     };
 
-export class Value<A> extends IBuilder<A> {
+export class Value<A extends ValueSpecAny> extends IBuilder<A> {
   static boolean<A extends Description & Default<boolean>>(a: A) {
     return new Value({
       type: "boolean" as const,
       ...a,
     });
   }
-  static string<A extends Description & NullableDefault<string> & Nullable & StringSpec>(a: A) {
+  static string<A extends Description & NullableDefault<DefaultString> & Nullable & StringSpec>(a: A) {
     return new Value({
       type: "string" as const,
       ...a,
-    });
+    } as Tag<"string", T.WithDescription<T.WithNullableDefault<T.WithNullable<T.ValueSpecString>, DefaultString>>>);
   }
   static number<A extends Description & NullableDefault<number> & Nullable & NumberSpec>(a: A) {
     return new Value({
       type: "number" as const,
       ...a,
-    });
+    } as Tag<"number", T.WithDescription<T.WithNullableDefault<T.WithNullable<T.ValueSpecNumber>, number>>>);
   }
   static enum<
     A extends Description &
@@ -74,20 +81,20 @@ export class Value<A> extends IBuilder<A> {
   }
   static object<
     A extends Description &
-      NullableDefault<Config<B>> & { values: readonly string[] | string[]; "value-names": Record<string, string> },
-    B
+      NullableDefault<{ [k: string]: unknown }> & {
+        "display-as": null | string;
+        "unique-by": null | string;
+        spec: Config<B>;
+        "value-names": Record<string, string>;
+      },
+    B extends ConfigSpec
   >(a: A) {
-    const { default: previousDefault, ...rest } = a;
-    if (previousDefault == null) {
-      return new Value({
-        type: "object" as const,
-        ...rest,
-      });
-    }
+    const { spec: previousSpec, ...rest } = a;
+    const spec = previousSpec.build();
     return new Value({
       type: "object" as const,
       ...rest,
-      default: previousDefault.build(),
+      spec,
     });
   }
   static union<
@@ -106,8 +113,9 @@ export class Value<A> extends IBuilder<A> {
         "unique-by": _UniqueBy | null;
       },
     Variants extends {
-      [key: string]: Config<unknown>;
-    }
+      [key: string]: Config<B>;
+    },
+    B extends ConfigSpec
   >(a: A) {
     const { variants: previousVariants, ...rest } = a;
     // deno-lint-ignore no-explicit-any
@@ -123,13 +131,10 @@ export class Value<A> extends IBuilder<A> {
     });
   }
 
-  static pointer<A>(a: Pointer<A>) {
+  static pointer<A extends ValueSpecAny>(a: Pointer<A>) {
     return new Value(a.build());
   }
-  static list<A extends List<B>, B>(a: A) {
-    return new Value({
-      type: "list" as const,
-      ...a.build(),
-    });
+  static list<A extends List<B>, B extends Tag<"list", ValueSpecList>>(a: A) {
+    return new Value(a.build());
   }
 }
diff --git a/types.ts b/types.ts
index d24698f..d5329b7 100644
--- a/types.ts
+++ b/types.ts
@@ -176,9 +176,9 @@ export type WithNullableDefault<T, Default> = T & {
 };
 
 export type WithDescription<T> = T & {
-  description?: string;
+  description?: null | string;
   name: string;
-  warning?: string;
+  warning?: null | string;
 };
 
 export type ListSpec<T> = {
@@ -212,7 +212,7 @@ export type DefaultString =
   | string
   | {
       /** The chars available for the randome generation */
-      charset?: string;
+      charset?: null | string;
       /** Length that we generate to */
       len: number;
     };
@@ -225,17 +225,17 @@ export type ValueSpecString = (
       "pattern-description": string;
     }
 ) & {
-  copyable?: boolean;
-  masked?: boolean;
-  placeholder?: string;
+  copyable?: null | boolean;
+  masked?: null | boolean;
+  placeholder?: null | string;
 };
 export type ValueSpecNumber = {
   /** Something like [3,6] or [0, *) */
-  range?: string;
-  integral?: boolean;
+  range?: null | string;
+  integral?: null | boolean;
   /** Used a description of the units */
-  units?: string;
-  placeholder?: number;
+  units?: null | string;
+  placeholder?: null | number;
 };
 export type ValueSpecBoolean = Record<string, unknown>;
 export type ValueSpecAny =
@@ -301,8 +301,8 @@ export type ValueSpecUnion = {
   /** What tag for the specification, for tag unions */
   tag: {
     id: string;
-    name?: string;
-    description?: string;
+    name?: null | string;
+    description?: null | string;
     "variant-names": {
       [key: string]: string;
     };
@@ -311,13 +311,13 @@ export type ValueSpecUnion = {
   variants: {
     [key: string]: ConfigSpec;
   };
-  "display-as"?: string;
-  "unique-by"?: UniqueBy;
+  "display-as"?: null | string;
+  "unique-by"?: null | UniqueBy;
 };
 export type ValueSpecObject = {
   spec: ConfigSpec;
-  "display-as"?: string;
-  "unique-by"?: UniqueBy;
+  "display-as"?: null | string;
+  "unique-by"?: null | UniqueBy;
 };
 export type ValueSpecList =
   | Subtype<"boolean", WithDescription<WithDefault<ListSpec<ValueSpecBoolean>, boolean[]>>>