diff --git a/src/backend/mod.rs b/src/backend/mod.rs
index 9e9f408..5844428 100644
--- a/src/backend/mod.rs
+++ b/src/backend/mod.rs
@@ -22,7 +22,7 @@ pub fn make_default_backend() -> anyhow::Result<Box<dyn Backend>> {
 
 /// A WebAssembly runtime backend.
 pub trait Backend {
-    fn load_module(&self, module: &[u8]) -> anyhow::Result<Arc<dyn Instance>>;
+    fn load_module(&self, abi: ScriptAbi, module: &[u8]) -> anyhow::Result<Arc<dyn Instance>>;
 }
 
 /// An instance of a WebAssembly module.
@@ -59,3 +59,101 @@ pub trait Instance {
 
     fn on_message(&self, panel_ud: u32, msg: Vec<u8>);
 }
+
+#[derive(Default)]
+pub struct ScriptAbi {
+    draw_cmds: Mutex<Vec<DrawCommand>>,
+    font_store: Arc<text::FontStore>,
+    font_families: Mutex<HashMap<String, u32>>,
+    loaded_fonts: RwLock<Vec<Arc<text::Font>>>,
+    text_layouts: RwLock<Slab<text::TextLayout>>,
+    message_store: RwLock<Slab<Vec<u8>>>,
+}
+
+impl ScriptAbi {
+    pub fn new(font_store: Arc<text::FontStore>) -> Self {
+        Self {
+            font_store,
+            ..Default::default()
+        }
+    }
+
+    pub fn start_draw(&self) {
+        let mut lock = self.draw_cmds.lock();
+        lock.clear();
+    }
+
+    pub fn draw_indexed(&self, vertices: &[MeshVertex], indices: &[MeshIndex]) {
+        self.draw_cmds.lock().push(DrawCommand::Mesh {
+            vertices: vertices.to_vec(),
+            indices: indices.to_vec(),
+        })
+    }
+
+    pub fn draw_text_layout(&self, id: u32, offset: Vec2, scale: f32, color: Color) {
+        // TODO multiple fonts per layout
+        let layouts = self.text_layouts.read();
+        let layout = layouts.get(id as usize).unwrap();
+        let glyphs = layout.glyphs.as_slice();
+        let loaded = self.loaded_fonts.read();
+        let font = loaded.get(layout.font_id as usize).unwrap();
+        let cmds = font.draw(glyphs, offset, scale, color);
+        self.draw_cmds.lock().extend(cmds.into_iter());
+    }
+
+    pub fn with_draw_commands(&self, f: impl FnOnce(&[DrawCommand])) {
+        f(self.draw_cmds.lock().as_slice());
+    }
+
+    pub fn font_load(&self, family: &str) -> u32 {
+        let mut family_cache = self.font_families.lock();
+
+        if let Some(cached) = family_cache.get(family) {
+            return *cached;
+        }
+
+        let font = self.font_store.load_font(family);
+        let mut loaded = self.loaded_fonts.write();
+        let id = loaded.len() as u32;
+        family_cache.insert(family.to_string(), id);
+        loaded.push(font);
+        id
+    }
+
+    pub fn text_layout_new(&self, font_id: u32, text: &str) -> u32 {
+        let loaded = self.loaded_fonts.read();
+        let font = loaded.get(font_id as usize).unwrap();
+        let layout = font.shape(text);
+        self.text_layouts.write().insert(layout) as u32
+    }
+
+    pub fn text_layout_delete(&self, id: u32) {
+        self.text_layouts.write().remove(id as usize);
+    }
+
+    pub fn text_layout_get_bounds(&self, id: u32, dst: &mut Rect) {
+        let src = self.text_layouts.read().get(id as usize).unwrap().bounds;
+        let _ = std::mem::replace(dst, src);
+    }
+
+    pub fn message_new(&self, data: Vec<u8>) -> u32 {
+        let mut store = self.message_store.write();
+        let id = store.insert(data) as u32;
+        id
+    }
+
+    pub fn message_free(&self, id: u32) {
+        let mut store = self.message_store.write();
+        store.remove(id as usize);
+    }
+
+    pub fn message_get_len(&self, id: u32) -> u32 {
+        self.message_store.read().get(id as usize).unwrap().len() as u32
+    }
+
+    pub fn message_get_data(&self, id: u32, dst: &mut [u8]) {
+        let store = self.message_store.read();
+        let src = store.get(id as usize).unwrap();
+        dst.copy_from_slice(src);
+    }
+}
diff --git a/src/backend/wasmtime.rs b/src/backend/wasmtime.rs
index 74f5f85..5af182a 100644
--- a/src/backend/wasmtime.rs
+++ b/src/backend/wasmtime.rs
@@ -3,15 +3,15 @@
 
 use std::ops::DerefMut;
 
-use super::{Arc, Backend, Instance, PanelId};
-use crate::{DrawCommand, ScriptAbi, ScriptAbiImpl};
+use super::{Arc, Backend, Instance, PanelId, ScriptAbi};
+use crate::DrawCommand;
 
 use canary_script::{Color, CursorEventKind, Rect, Vec2};
 use parking_lot::Mutex;
 
-type Caller<'a> = wasmtime::Caller<'a, ScriptAbiImpl>;
-type Store = wasmtime::Store<ScriptAbiImpl>;
-type Linker = wasmtime::Linker<ScriptAbiImpl>;
+type Caller<'a> = wasmtime::Caller<'a, ScriptAbi>;
+type Store = wasmtime::Store<ScriptAbi>;
+type Linker = wasmtime::Linker<ScriptAbi>;
 
 pub struct WasmtimeBackend {
     engine: wasmtime::Engine,
@@ -30,9 +30,8 @@ impl WasmtimeBackend {
 }
 
 impl Backend for WasmtimeBackend {
-    fn load_module(&self, module: &[u8]) -> anyhow::Result<Arc<dyn Instance>> {
+    fn load_module(&self, abi: ScriptAbi, module: &[u8]) -> anyhow::Result<Arc<dyn Instance>> {
         let module = wasmtime::Module::new(&self.engine, module)?;
-        let abi = ScriptAbiImpl::default();
         let mut store = wasmtime::Store::new(&self.engine, abi);
         let mut linker = Linker::new(&self.engine);
         WasmtimeInstance::link(&mut linker)?;
diff --git a/src/lib.rs b/src/lib.rs
index c46fc26..c32bd15 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,20 +10,26 @@ use std::sync::Arc;
 pub mod backend;
 pub mod text;
 
-use backend::{Backend, Instance};
+use backend::{Backend, Instance, ScriptAbi};
+use text::FontStore;
 
 /// The main interface to Canary.
 pub struct Runtime {
     backend: Box<dyn Backend>,
+    font_store: Arc<FontStore>,
 }
 
 impl Runtime {
     pub fn new(backend: Box<dyn Backend>) -> anyhow::Result<Self> {
-        Ok(Self { backend })
+        Ok(Self {
+            backend,
+            font_store: Arc::new(FontStore::new()),
+        })
     }
 
     pub fn load_module(&self, module: &[u8]) -> anyhow::Result<Script> {
-        let instance = self.backend.load_module(module)?;
+        let abi = ScriptAbi::new(self.font_store.to_owned());
+        let instance = self.backend.load_module(abi, module)?;
 
         Ok(Script {
             instance,
@@ -83,28 +89,6 @@ impl Panel {
 /// Proportion constant between pixels (at 96dpi) to millimeters (Canary's unit measurement).
 pub const PX_PER_MM: f32 = 25.4 / 96.0;
 
-/// Low-level script API callbacks.
-///
-/// If you're a casual user of Canary the struct you're looking for is
-/// [ScriptAbiImpl]. This trait exists to help with making mocks for testing.
-pub trait ScriptAbi {
-    fn start_draw(&self);
-    fn draw_indexed(&self, vertices: &[MeshVertex], indices: &[MeshIndex]);
-    fn draw_text_layout(&self, id: u32, offset: Vec2, scale: f32, color: Color);
-    fn with_draw_commands(&self, f: impl FnOnce(&[DrawCommand]));
-
-    fn font_load(&self, family: &str) -> u32;
-
-    fn text_layout_new(&self, font_id: u32, text: &str) -> u32;
-    fn text_layout_delete(&self, id: u32);
-    fn text_layout_get_bounds(&self, id: u32, rect: &mut Rect);
-
-    fn message_new(&self, data: Vec<u8>) -> u32;
-    fn message_free(&self, id: u32);
-    fn message_get_len(&self, id: u32) -> u32;
-    fn message_get_data(&self, id: u32, dst: &mut [u8]);
-}
-
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct PanelId(pub(crate) usize);
 
@@ -116,95 +100,3 @@ pub enum DrawCommand {
         indices: Vec<MeshIndex>,
     },
 }
-
-/// The standard [ScriptAbi] implementation to use.
-#[derive(Default)]
-pub struct ScriptAbiImpl {
-    draw_cmds: Mutex<Vec<DrawCommand>>,
-    font_store: text::FontStore,
-    font_families: Mutex<HashMap<String, u32>>,
-    loaded_fonts: RwLock<Vec<Arc<text::Font>>>,
-    text_layouts: RwLock<Slab<text::TextLayout>>,
-    message_store: RwLock<Slab<Vec<u8>>>,
-}
-
-impl ScriptAbi for ScriptAbiImpl {
-    fn start_draw(&self) {
-        let mut lock = self.draw_cmds.lock();
-        lock.clear();
-    }
-
-    fn draw_indexed(&self, vertices: &[MeshVertex], indices: &[MeshIndex]) {
-        self.draw_cmds.lock().push(DrawCommand::Mesh {
-            vertices: vertices.to_vec(),
-            indices: indices.to_vec(),
-        })
-    }
-
-    fn draw_text_layout(&self, id: u32, offset: Vec2, scale: f32, color: Color) {
-        // TODO multiple fonts per layout
-        let layouts = self.text_layouts.read();
-        let layout = layouts.get(id as usize).unwrap();
-        let glyphs = layout.glyphs.as_slice();
-        let loaded = self.loaded_fonts.read();
-        let font = loaded.get(layout.font_id as usize).unwrap();
-        let cmds = font.draw(glyphs, offset, scale, color);
-        self.draw_cmds.lock().extend(cmds.into_iter());
-    }
-
-    fn with_draw_commands(&self, f: impl FnOnce(&[DrawCommand])) {
-        f(self.draw_cmds.lock().as_slice());
-    }
-
-    fn font_load(&self, family: &str) -> u32 {
-        let mut family_cache = self.font_families.lock();
-
-        if let Some(cached) = family_cache.get(family) {
-            return *cached;
-        }
-
-        let font = self.font_store.load_font(family);
-        let mut loaded = self.loaded_fonts.write();
-        let id = loaded.len() as u32;
-        family_cache.insert(family.to_string(), id);
-        loaded.push(font);
-        id
-    }
-
-    fn text_layout_new(&self, font_id: u32, text: &str) -> u32 {
-        let loaded = self.loaded_fonts.read();
-        let font = loaded.get(font_id as usize).unwrap();
-        let layout = font.shape(text);
-        self.text_layouts.write().insert(layout) as u32
-    }
-
-    fn text_layout_delete(&self, id: u32) {
-        self.text_layouts.write().remove(id as usize);
-    }
-
-    fn text_layout_get_bounds(&self, id: u32, dst: &mut Rect) {
-        let src = self.text_layouts.read().get(id as usize).unwrap().bounds;
-        let _ = std::mem::replace(dst, src);
-    }
-
-    fn message_new(&self, data: Vec<u8>) -> u32 {
-        let mut store = self.message_store.write();
-        let id = store.insert(data) as u32;
-        id
-    }
-
-    fn message_free(&self, id: u32) {
-        let mut store = self.message_store.write();
-        store.remove(id as usize);
-    }
-
-    fn message_get_len(&self, id: u32) -> u32 {
-        self.message_store.read().get(id as usize).unwrap().len() as u32
-    }
-
-    fn message_get_data(&self, id: u32, dst: &mut [u8]) {
-        let store = self.message_store.read();
-        let src = store.get(id as usize).unwrap();
-        dst.copy_from_slice(src);
-    }
-}