diff --git a/Cargo.lock b/Cargo.lock
index 8339f26..874cafc 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -588,6 +588,7 @@ dependencies = [
  "serde",
  "serde-wasm-bindgen 0.6.5",
  "serde_with",
+ "strum",
  "thiserror",
  "tsify",
  "wasm-bindgen",
diff --git a/ic10emu/src/lib.rs b/ic10emu/src/lib.rs
index fce9408..11e9cd9 100644
--- a/ic10emu/src/lib.rs
+++ b/ic10emu/src/lib.rs
@@ -449,8 +449,8 @@ impl Network {
 
 #[derive(Debug, Default, Clone, Serialize, Deserialize)]
 pub struct Prefab {
-    name: String,
-    hash: i32,
+    pub name: String,
+    pub hash: i32,
 }
 
 impl Prefab {
@@ -481,7 +481,7 @@ pub struct DeviceTemplate {
     pub name: Option<String>,
     pub prefab_name: Option<String>,
     pub slots: Vec<SlotTemplate>,
-    pub reagents: HashMap<ReagentMode, HashMap<i32, f64>>,
+    // pub reagents: HashMap<ReagentMode, HashMap<i32, f64>>,
     pub connections: Vec<Connection>,
     pub fields: HashMap<LogicType, LogicField>,
 }
@@ -1089,7 +1089,8 @@ impl VM {
             name_hash,
             prefab: template.prefab_name.map(|name| Prefab::new(&name)),
             slots,
-            reagents: template.reagents,
+            // reagents: template.reagents,
+            reagents: HashMap::new(),
             ic,
             connections: template.connections,
             fields,
diff --git a/ic10emu_wasm/Cargo.toml b/ic10emu_wasm/Cargo.toml
index 64ad699..05c907d 100644
--- a/ic10emu_wasm/Cargo.toml
+++ b/ic10emu_wasm/Cargo.toml
@@ -21,6 +21,11 @@ serde_with = "3.7.0"
 tsify = { version = "0.4.5", default-features = false, features = ["js", "wasm-bindgen"] }
 thiserror = "1.0.58"
 
+[build-dependencies]
+ic10emu = { path = "../ic10emu" }
+strum = { version = "0.26.2"}
+itertools = "0.12.1"
+
 [features]
 default = ["console_error_panic_hook"]
 console_error_panic_hook = ["dep:console_error_panic_hook"]
diff --git a/ic10emu_wasm/build.rs b/ic10emu_wasm/build.rs
index 55a368f..7a1ea33 100644
--- a/ic10emu_wasm/build.rs
+++ b/ic10emu_wasm/build.rs
@@ -5,18 +5,59 @@ use std::{
     path::Path,
 };
 
+use itertools::Itertools;
+use strum::IntoEnumIterator;
+
 fn main() {
     let out_dir = env::var_os("OUT_DIR").unwrap();
     let dest_path = Path::new(&out_dir).join("ts_types.rs");
     let output_file = File::create(dest_path).unwrap();
     let mut writer = BufWriter::new(&output_file);
 
+    let mut ts_types: String = String::new();
+
+    let lt_tsunion: String = Itertools::intersperse(
+        ic10emu::grammar::generated::LogicType::iter().map(|lt| format!("\"{}\"", lt.as_ref())),
+        "\n  | ".to_owned(),
+    )
+    .collect();
+    let lt_tstype = format!("\nexport type LogicType = {};", lt_tsunion);
+    ts_types.push_str(&lt_tstype);
+
+    let slt_tsunion: String = Itertools::intersperse(
+        ic10emu::grammar::generated::SlotLogicType::iter().map(|slt| format!("\"{}\"", slt.as_ref())),
+        "\n  | ".to_owned(),
+    )
+    .collect();
+    let slt_tstype = format!("\nexport type SlotLogicType = {};", slt_tsunion);
+    ts_types.push_str(&slt_tstype);
+
+    let bm_tsunion: String = Itertools::intersperse(
+        ic10emu::grammar::generated::BatchMode::iter().map(|bm| format!("\"{}\"", bm.as_ref())),
+        "\n  | ".to_owned(),
+    )
+    .collect();
+    let bm_tstype = format!("\nexport type BatchMode = {};", bm_tsunion);
+    ts_types.push_str(&bm_tstype);
+
+    let rm_tsunion: String = Itertools::intersperse(
+        ic10emu::grammar::generated::ReagentMode::iter().map(|rm| format!("\"{}\"", rm.as_ref())),
+        "\n  | ".to_owned(),
+    )
+    .collect();
+    let rm_tstype = format!("\nexport type ReagentMode = {};", rm_tsunion);
+    ts_types.push_str(&rm_tstype);
+
     let infile = Path::new("src/types.ts");
     let contents = fs::read_to_string(infile).unwrap();
+
+    ts_types.push('\n');
+    ts_types.push_str(&contents);
+
     write!(
         &mut writer,
         "#[wasm_bindgen(typescript_custom_section)]\n\
-        const TYPES: &'static str = r#\"{contents}\"#;
+        const TYPES: &'static str = r#\"{ts_types}\"#;
         "
     )
     .unwrap();
diff --git a/ic10emu_wasm/src/lib.rs b/ic10emu_wasm/src/lib.rs
index 2cd1d7b..f554509 100644
--- a/ic10emu_wasm/src/lib.rs
+++ b/ic10emu_wasm/src/lib.rs
@@ -2,7 +2,7 @@
 mod utils;
 mod types;
 
-use ic10emu::grammar::{LogicType, SlotLogicType};
+use ic10emu::{grammar::{LogicType, SlotLogicType}, DeviceTemplate};
 use serde::{Deserialize, Serialize};
 use types::{Registers, Stack};
 
@@ -55,18 +55,18 @@ impl DeviceRef {
     }
 
     #[wasm_bindgen(getter, js_name = "nameHash")]
-    pub fn name_hash(&self) -> Option<f64> {
+    pub fn name_hash(&self) -> Option<i32> {
         self.device.borrow().name_hash
     }
 
     #[wasm_bindgen(getter, js_name = "prefabName")]
     pub fn prefab_name(&self) -> Option<String> {
-        self.device.borrow().prefab_name.clone()
+        self.device.borrow().prefab.as_ref().map(|prefab| prefab.name.clone())
     }
 
     #[wasm_bindgen(getter, js_name = "prefabHash")]
     pub fn prefab_hash(&self) -> Option<i32> {
-        self.device.borrow().prefab_hash
+        self.device.borrow().prefab.as_ref().map(|prefab| prefab.hash)
     }
 
     #[wasm_bindgen(getter, skip_typescript)]
@@ -351,6 +351,12 @@ impl VM {
         Ok(self.vm.borrow_mut().add_device(network)?)
     }
 
+    #[wasm_bindgen(js_name = "addDeviceFromTemplate", skip_typescript)]
+    pub fn add_device_from_template(&self, template: JsValue) -> Result<u32, JsError> {
+        let template: DeviceTemplate = serde_wasm_bindgen::from_value(template)?;
+        Ok(self.vm.borrow_mut().add_device_from_template(template)?)
+    }
+
     #[wasm_bindgen(js_name = "getDevice")]
     pub fn get_device(&self, id: u32) -> Option<DeviceRef> {
         let device = self.vm.borrow().get_device(id);
diff --git a/ic10emu_wasm/src/types.ts b/ic10emu_wasm/src/types.ts
index a38f3ce..8c97f7f 100644
--- a/ic10emu_wasm/src/types.ts
+++ b/ic10emu_wasm/src/types.ts
@@ -4,7 +4,8 @@ export interface LogicField {
   field_type: FieldType;
   value: number;
 }
-export type Fields = Map<string, LogicField>;
+export type LogicFields = Map<LogicType, LogicField>;
+export type SlotLogicFields = Map<SlotLogicType, LogicField>;
 
 export type SlotType =
   | "AccessCard"
@@ -46,12 +47,12 @@ export interface SlotOccupant {
   readonly quantity: number;
   readonly max_quantity: number;
   readonly damage: number;
-  readonly fields: Fields;
+  readonly fields: SlotLogicFields;
 }
 export interface Slot {
   readonly typ: SlotType;
   readonly occupant: SlotOccupant | undefined;
-  readonly fields: Fields;
+  readonly fields: SlotLogicFields;
 }
 
 export type Reagents = Map<string, Map<number, number>>;
@@ -80,10 +81,10 @@ export type DeviceSpec = {
   };
   readonly connection: number | undefined;
 };
-export type LogicType = { readonly LogicType: string };
-export type SlotLogicType = { readonly SlotLogicType: string };
-export type BatchMode = { readonly BatchMode: string };
-export type ReagentMode = { readonly ReagentMode: string };
+export type OperandLogicType = { readonly LogicType: string };
+export type OperandSlotLogicType = { readonly SlotLogicType: string };
+export type OperandBatchMode = { readonly BatchMode: string };
+export type OperandReagentMode = { readonly ReagentMode: string };
 export type Identifier = { readonly Identifier: { name: string } };
 
 export type NumberFloat = { readonly Float: number };
@@ -106,10 +107,10 @@ export type Operand =
   | RegisterSpec
   | DeviceSpec
   | NumberOperand
-  | LogicType
-  | SlotLogicType
-  | BatchMode
-  | ReagentMode
+  | OperandLogicType
+  | OperandSlotLogicType
+  | OperandBatchMode
+  | OperandReagentMode
   | Identifier;
 
 export type Alias = RegisterSpec | DeviceSpec;
@@ -141,7 +142,7 @@ export interface Program {
 }
 
 export interface DeviceRef {
-  readonly fields: Fields;
+  readonly fields: LogicFields;
   readonly slots: Slot[];
   readonly reagents: Reagents;
   readonly connections: Connection[];
@@ -149,5 +150,29 @@ export interface DeviceRef {
   readonly defines?: Defines | undefined;
   readonly pins?: Pins;
   readonly program?: Program;
-  getSlotFields(slot: number): Fields;
+  getSlotFields(slot: number): SlotLogicFields;
+}
+
+export interface SlotOccupantTemplate {
+  id?: number;
+  fields: { [key in SlotLogicType]?: LogicField };
+}
+
+export interface SlotTemplate {
+  typ: SlotType;
+  occupant?: SlotOccupantTemplate;
+}
+
+export interface DeviceTemplate {
+  id?: number;
+  name?: string;
+  prefab_name?: string;
+  slots: SlotTemplate[];
+  // reagents: { [key: string]: float}
+  connections: Connection[];
+  fields: { [key in LogicType]?: LogicField };
+}
+
+export interface VM {
+  addDeviceFromTemplate(template: DeviceTemplate): number
 }
diff --git a/www/src/ts/editor/index.ts b/www/src/ts/editor/index.ts
index d3ceda7..4cdf718 100644
--- a/www/src/ts/editor/index.ts
+++ b/www/src/ts/editor/index.ts
@@ -44,7 +44,7 @@ export class IC10Editor extends BaseElement {
   };
   sessions: Map<number, Ace.EditSession>;
 
-  @state() active_session: number = 0;
+  @state() active_session: number = 1;
 
   active_line_markers: Map<number, number | null> = new Map();
   languageProvider?: LanguageProvider;
diff --git a/www/src/ts/session.ts b/www/src/ts/session.ts
index 97e0706..ebb7556 100644
--- a/www/src/ts/session.ts
+++ b/www/src/ts/session.ts
@@ -74,7 +74,7 @@ export class Session extends EventTarget {
     this._programs = new Map();
     this._errors = new Map();
     this._save_timeout = undefined;
-    this._activeIC = 0;
+    this._activeIC = 1;
     this._activeLines = new Map();
     this.loadFromFragment();
 
@@ -201,7 +201,7 @@ export class Session extends EventTarget {
   async loadFromFragment() {
     const fragment = window.location.hash.slice(1);
     if (fragment === "demo") {
-      this._programs = new Map([[0, demoCode]]);
+      this._programs = new Map([[1, demoCode]]);
       this._fireOnLoad();
       return;
     }
@@ -213,7 +213,7 @@ export class Session extends EventTarget {
         const data = getJson(txt);
         if (data === null) {
           // backwards compatible
-          this._programs = new Map([[0, txt]]);
+          this._programs = new Map([[1, txt]]);
           this, this._fireOnLoad();
           return;
         }
diff --git a/www/src/ts/virtual_machine/base_device.ts b/www/src/ts/virtual_machine/base_device.ts
index 6cd1dbc..af2be7f 100644
--- a/www/src/ts/virtual_machine/base_device.ts
+++ b/www/src/ts/virtual_machine/base_device.ts
@@ -2,7 +2,7 @@ import { property, state } from "lit/decorators.js";
 
 import {
   DeviceRef,
-  Fields,
+  LogicFields,
   Reagents,
   Slot,
   Connection,
@@ -25,7 +25,7 @@ export declare class VMDeviceMixinInterface {
   name: string | null;
   nameHash: number | null;
   prefabName: string | null;
-  fields: Fields;
+  fields: LogicFields;
   slots: Slot[];
   reagents: Reagents;
   connections: Connection[];
@@ -53,7 +53,7 @@ export const VMDeviceMixin = <T extends Constructor<LitElement>>(
     @state() accessor name: string | null = null;
     @state() accessor nameHash: number | null = null;
     @state() accessor prefabName: string | null;
-    @state() accessor fields: Fields;
+    @state() accessor fields: LogicFields;
     @state() accessor slots: Slot[];
     @state() accessor reagents: Reagents;
     @state() accessor connections: Connection[];