diff --git a/Cargo.lock b/Cargo.lock
index 82183245b4..a6ae17bbd0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1390,6 +1390,7 @@ dependencies = [
  "serde",
  "serde_json",
  "ts-rs",
+ "unicode-width",
 ]
 
 [[package]]
diff --git a/crates/fresh-core/Cargo.toml b/crates/fresh-core/Cargo.toml
index 35ccf3b454..b53d1b684f 100644
--- a/crates/fresh-core/Cargo.toml
+++ b/crates/fresh-core/Cargo.toml
@@ -15,6 +15,7 @@ schemars.workspace = true
 anyhow.workspace = true
 lsp-types.workspace = true
 ts-rs.workspace = true
+unicode-width = "0.2"
 rquickjs = { workspace = true, optional = true }
 rquickjs-serde = { workspace = true, optional = true }
 
diff --git a/crates/fresh-core/src/display_width.rs b/crates/fresh-core/src/display_width.rs
new file mode 100644
index 0000000000..487b9aed93
--- /dev/null
+++ b/crates/fresh-core/src/display_width.rs
@@ -0,0 +1,58 @@
+//! Display width calculation for Unicode text.
+//!
+//! The single source of truth for "how many terminal columns does this text
+//! occupy", backed by the `unicode-width` crate. Used for cursor positioning,
+//! line wrapping, and UI layout with CJK characters, emoji, and other
+//! double-width or zero-width characters.
+//!
+//! This lives in `fresh-core` so that both the editor (layout/rendering) and
+//! the plugin runtime (the `charWidth` / `stringWidth` plugin APIs) compute
+//! width with the *same* logic — plugins must not re-derive their own width
+//! tables, or their measurements drift from how the editor actually lays out
+//! cells.
+
+use unicode_width::{UnicodeWidthChar, UnicodeWidthStr};
+
+/// Display width of a single character, in terminal columns.
+///
+/// Returns 0 for control and zero-width characters, 2 for CJK/fullwidth
+/// characters and most emoji, and 1 for everything else.
+#[inline]
+pub fn char_width(c: char) -> usize {
+    // unicode_width returns None for control characters.
+    c.width().unwrap_or(0)
+}
+
+/// Display width of a string, in terminal columns (the sum of its characters'
+/// widths). Use this instead of `.chars().count()` for visual layout.
+#[inline]
+pub fn str_width(s: &str) -> usize {
+    s.width()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ascii() {
+        assert_eq!(str_width("Hello"), 5);
+        assert_eq!(str_width(""), 0);
+        assert_eq!(char_width('a'), 1);
+    }
+
+    #[test]
+    fn cjk_and_emoji_are_two_columns() {
+        assert_eq!(char_width('你'), 2);
+        assert_eq!(char_width('🚀'), 2);
+        assert_eq!(str_width("你好"), 4);
+        assert_eq!(str_width("Hi🚀"), 4);
+    }
+
+    #[test]
+    fn control_and_zero_width_are_zero() {
+        assert_eq!(char_width('\0'), 0);
+        assert_eq!(char_width('\t'), 0);
+        assert_eq!(char_width('\u{200B}'), 0); // zero-width space
+    }
+}
diff --git a/crates/fresh-core/src/lib.rs b/crates/fresh-core/src/lib.rs
index 40c67184cd..abab5a8263 100644
--- a/crates/fresh-core/src/lib.rs
+++ b/crates/fresh-core/src/lib.rs
@@ -123,6 +123,7 @@ impl std::fmt::Display for WindowTerminalId {
 }
 
 pub mod config;
+pub mod display_width;
 pub mod file_explorer;
 pub mod file_uri;
 pub mod menu;
diff --git a/crates/fresh-editor/plugins/lib/fresh.d.ts b/crates/fresh-editor/plugins/lib/fresh.d.ts
index 8053570a73..b4908b37bc 100644
--- a/crates/fresh-editor/plugins/lib/fresh.d.ts
+++ b/crates/fresh-editor/plugins/lib/fresh.d.ts
@@ -2523,6 +2523,21 @@ interface EditorAPI {
 	*/
 	clearConcealsInRange(bufferId: number, start: number, end: number): boolean;
 	/**
+	* Display width of a single Unicode code point, in terminal columns
+	* (0 for control/zero-width, 2 for CJK/fullwidth and most emoji, else 1).
+	*
+	* Backed by the editor's own width logic (`fresh_core::display_width`), so
+	* plugins measure width exactly as the editor lays out cells — no
+	* per-plugin width tables. An invalid code point returns 0.
+	*/
+	charWidth(codePoint: number): number;
+	/**
+	* Display width of a string, in terminal columns (the sum of its
+	* characters' widths). Prefer this over per-character `charWidth` calls
+	* when measuring whole cells — one boundary crossing instead of many.
+	*/
+	stringWidth(text: string): number;
+	/**
 	* Add a collapsed fold range. Hides bytes [start, end) from
 	* rendering — the line containing `start - 1` (the fold "header")
 	* stays visible, while subsequent lines covered by the range are
diff --git a/crates/fresh-editor/src/primitives/display_width.rs b/crates/fresh-editor/src/primitives/display_width.rs
index f38c28fc97..5a0adab6d4 100644
--- a/crates/fresh-editor/src/primitives/display_width.rs
+++ b/crates/fresh-editor/src/primitives/display_width.rs
@@ -5,27 +5,11 @@
 //! cursor positioning, line wrapping, and UI layout with CJK characters,
 //! emoji, and other double-width or zero-width characters.
 
-use unicode_width::{UnicodeWidthChar, UnicodeWidthStr};
-
-/// Calculate the display width of a single character.
-///
-/// Returns 0 for control characters and zero-width characters,
-/// 2 for CJK/fullwidth characters and emoji,
-/// 1 for most other characters.
-#[inline]
-pub fn char_width(c: char) -> usize {
-    // unicode_width returns None for control characters
-    c.width().unwrap_or(0)
-}
-
-/// Calculate the display width of a string.
-///
-/// This is the sum of display widths of all characters in the string.
-/// Use this instead of `.chars().count()` when calculating visual layout.
-#[inline]
-pub fn str_width(s: &str) -> usize {
-    s.width()
-}
+// `char_width` / `str_width` are the single source of truth in `fresh-core`,
+// shared with the plugin runtime's `charWidth` / `stringWidth` APIs so plugins
+// measure width exactly the way the editor lays out cells. The editor-specific
+// byte/column helpers below build on them.
+pub use fresh_core::display_width::{char_width, str_width};
 
 /// Extension trait for convenient width calculation on string types.
 pub trait DisplayWidth {
diff --git a/crates/fresh-plugin-runtime/src/backend/quickjs_backend.rs b/crates/fresh-plugin-runtime/src/backend/quickjs_backend.rs
index 89b578748f..c8271a4c23 100644
--- a/crates/fresh-plugin-runtime/src/backend/quickjs_backend.rs
+++ b/crates/fresh-plugin-runtime/src/backend/quickjs_backend.rs
@@ -3540,6 +3540,27 @@ impl JsEditorApi {
             .is_ok()
     }
 
+    // === Text measurement ===
+
+    /// Display width of a single Unicode code point, in terminal columns
+    /// (0 for control/zero-width, 2 for CJK/fullwidth and most emoji, else 1).
+    ///
+    /// Backed by the editor's own width logic (`fresh_core::display_width`), so
+    /// plugins measure width exactly as the editor lays out cells — no
+    /// per-plugin width tables. An invalid code point returns 0.
+    pub fn char_width(&self, code_point: u32) -> u32 {
+        char::from_u32(code_point)
+            .map(fresh_core::display_width::char_width)
+            .unwrap_or(0) as u32
+    }
+
+    /// Display width of a string, in terminal columns (the sum of its
+    /// characters' widths). Prefer this over per-character `charWidth` calls
+    /// when measuring whole cells — one boundary crossing instead of many.
+    pub fn string_width(&self, text: String) -> u32 {
+        fresh_core::display_width::str_width(&text) as u32
+    }
+
     // === Folds ===
 
     /// Add a collapsed fold range. Hides bytes [start, end) from
diff --git a/crates/fresh-plugin-runtime/src/ts_export.rs b/crates/fresh-plugin-runtime/src/ts_export.rs
index 47580116ef..5a742e4e25 100644
--- a/crates/fresh-plugin-runtime/src/ts_export.rs
+++ b/crates/fresh-plugin-runtime/src/ts_export.rs
@@ -1355,6 +1355,8 @@ mod tests {
             "addConceal",
             "clearConcealNamespace",
             "clearConcealsInRange",
+            "charWidth",
+            "stringWidth",
             "addSoftBreak",
             "clearSoftBreakNamespace",
             "clearSoftBreaksInRange",