diff --git a/src/app/automation.rs b/src/app/automation.rs
index 6ea9c4f3d..eee846b2b 100644
--- a/src/app/automation.rs
+++ b/src/app/automation.rs
@@ -565,6 +565,27 @@ mod tests {
         assert_eq!(app.automation_op(r#"{"op":"run"}"#)["ok"], false);
     }
 
+    #[test]
+    fn ucs_interactive_inline_args() {
+        // `UCS Z 90` must drive the interactive UCS command step-by-step (option
+        // "Z" then value "90") and rotate the active UCS 90° about Z. (#169)
+        let mut app = OpenCADStudio::new_for_test();
+        app.automation_op(r#"{"op":"new"}"#);
+        app.automation_op(r#"{"op":"run","cmd":"UCS Z 90"}"#);
+        let i = app.active_tab;
+        let ucs = app.tabs[i]
+            .active_ucs
+            .as_ref()
+            .expect("UCS Z 90 should set an active UCS");
+        // 90° about Z sends the X axis (1,0,0) → (0,1,0).
+        assert!(
+            ucs.x_axis.x.abs() < 1e-6 && (ucs.x_axis.y - 1.0).abs() < 1e-6,
+            "x_axis after UCS Z 90 = ({}, {})",
+            ucs.x_axis.x,
+            ucs.x_axis.y
+        );
+    }
+
     #[test]
     fn save_then_open_round_trips() {
         let mut app = OpenCADStudio::new_for_test();
diff --git a/src/app/cmd_result.rs b/src/app/cmd_result.rs
index 39cba5ede..2315f2107 100644
--- a/src/app/cmd_result.rs
+++ b/src/app/cmd_result.rs
@@ -567,6 +567,15 @@ impl OpenCADStudio {
                 self.restore_pre_cmd_tangent();
                 let _ = self.dispatch_command(&cmd);
             }
+            CmdResult::Dispatch(cmd) => {
+                // End this interactive front-end, then run the assembled command
+                // through the normal dispatcher. Selection is left untouched.
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.tabs[i].scene.clear_preview_wire();
+                self.restore_pre_cmd_tangent();
+                let _ = self.dispatch_command(&cmd);
+            }
             CmdResult::MatchEntityLayer { dest, src } => {
                 self.tabs[i].active_cmd = None;
                 self.tabs[i].snap_result = None;
diff --git a/src/app/commands.rs b/src/app/commands.rs
index ed9ae96c5..1a0ac49c0 100644
--- a/src/app/commands.rs
+++ b/src/app/commands.rs
@@ -3618,8 +3618,18 @@ impl OpenCADStudio {
                 }
             }
 
-            // ── UCS management ───────────────────────────────────────────
-            cmd if cmd == "UCS" || cmd.starts_with("UCS ") => {
+            // Bare UCS → interactive front-end (option then value as steps), so
+            // `UCS Z 90` is typable in the command line and works headlessly.
+            // The front-end delegates back to the inline handler below. (#169)
+            "UCS" => {
+                use crate::modules::view::ucs_cmd::UcsCommand;
+                let cmd_obj = UcsCommand::new();
+                self.command_line.push_info(&cmd_obj.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(cmd_obj));
+            }
+
+            // ── UCS management (inline `UCS <option> …`) ─────────────────────
+            cmd if cmd.starts_with("UCS ") => {
                 use super::helpers::{ucs_rotated_z, ucs_to_wcs, ucs_z_axis};
                 use acadrust::tables::Ucs;
                 use acadrust::types::Vector3;
diff --git a/src/command/mod.rs b/src/command/mod.rs
index fc3c20cb6..99f91ed85 100644
--- a/src/command/mod.rs
+++ b/src/command/mod.rs
@@ -135,6 +135,12 @@ pub enum CmdResult {
     /// End the selection-gather phase and re-dispatch the named command
     /// with the gathered handles installed as the active scene selection.
     Relaunch(String, Vec<Handle>),
+    /// End the command and dispatch the given command string. Used by an
+    /// interactive front-end that gathered its arguments step-by-step and
+    /// delegates execution to an existing inline command handler (e.g. UCS
+    /// collecting an option + value, then running `UCS Z 90`). Unlike
+    /// `Relaunch` it does not touch the selection.
+    Dispatch(String),
     /// Move `dest` entities to the layer of the `src` entity; end command.
     MatchEntityLayer { dest: Vec<Handle>, src: Handle },
     /// Copy all visual properties (layer/color/linetype/lineweight) from `src` to `dest`; end command.
diff --git a/src/modules/view/mod.rs b/src/modules/view/mod.rs
index 50b9b3d17..32e9a67f4 100644
--- a/src/modules/view/mod.rs
+++ b/src/modules/view/mod.rs
@@ -15,6 +15,7 @@ mod solid;
 mod tile_horiz;
 mod tile_vert;
 mod tool_palettes;
+pub mod ucs_cmd;
 mod ucs_icon;
 mod view_front;
 mod view_iso;
diff --git a/src/modules/view/ucs_cmd.rs b/src/modules/view/ucs_cmd.rs
new file mode 100644
index 000000000..f620aa150
--- /dev/null
+++ b/src/modules/view/ucs_cmd.rs
@@ -0,0 +1,110 @@
+//! Interactive front-end for the UCS command.
+//!
+//! Bare `UCS` enters this command so the option and its value are entered
+//! step-by-step — `UCS` ⏎ → option ⏎ → value ⏎ — and so a single line
+//! `UCS Z 90` (typed in the command line with Space between tokens, or sent
+//! headless as `{"op":"run","cmd":"UCS Z 90"}`) feeds the option then the value
+//! as text steps. Execution is delegated to the existing inline `UCS …` handler
+//! via [`CmdResult::Dispatch`], so the coordinate-system math and persistence
+//! stay in one place. (#169)
+
+use crate::command::{CadCommand, CmdResult};
+use glam::DVec3;
+
+#[derive(Default)]
+pub struct UcsCommand {
+    /// The chosen option keyword (uppercased), once entered; `None` until then.
+    option: Option<String>,
+}
+
+impl UcsCommand {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Options that take no further argument and execute immediately.
+    fn is_zero_arg(opt: &str) -> bool {
+        matches!(opt, "W" | "WORLD" | "LIST" | "?")
+    }
+
+    /// Options whose argument is a coordinate (so a click is accepted too).
+    fn takes_point(opt: &str) -> bool {
+        matches!(opt, "ORIGIN" | "O")
+    }
+
+    /// Options that expect one more typed argument (angle or name).
+    fn takes_value(opt: &str) -> bool {
+        matches!(
+            opt,
+            "Z" | "X" | "Y" | "ORIGIN" | "O" | "SAVE" | "S" | "DELETE" | "DEL" | "D"
+        )
+    }
+}
+
+impl CadCommand for UcsCommand {
+    fn name(&self) -> &'static str {
+        "UCS"
+    }
+
+    fn prompt(&self) -> String {
+        match self.option.as_deref() {
+            None => "UCS  option [World/Z/X/Y/Origin/Save/Delete] or name:".into(),
+            Some("Z") => "UCS  rotation angle about Z (degrees):".into(),
+            Some("X") => "UCS  rotation angle about X (degrees):".into(),
+            Some("Y") => "UCS  rotation angle about Y (degrees):".into(),
+            Some("ORIGIN") | Some("O") => "UCS  new origin point:".into(),
+            Some("SAVE") | Some("S") => "UCS  name to save current UCS as:".into(),
+            Some("DELETE") | Some("DEL") | Some("D") => "UCS  name of UCS to delete:".into(),
+            Some(_) => "UCS  value:".into(),
+        }
+    }
+
+    fn wants_text_input(&self) -> bool {
+        true
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        let t = text.trim();
+        match self.option.take() {
+            // First token: the option keyword (or a named UCS to restore).
+            None => {
+                if t.is_empty() {
+                    // Bare Enter → list (delegate to inline `UCS`).
+                    return Some(CmdResult::Dispatch("UCS LIST".into()));
+                }
+                let up = t.to_uppercase();
+                if Self::is_zero_arg(&up) {
+                    Some(CmdResult::Dispatch(format!("UCS {up}")))
+                } else if Self::takes_value(&up) {
+                    // Needs a value next; keep the command active and re-prompt.
+                    self.option = Some(up);
+                    Some(CmdResult::NeedPoint)
+                } else {
+                    // Not a keyword → a named UCS to activate.
+                    Some(CmdResult::Dispatch(format!("UCS {t}")))
+                }
+            }
+            // Second token: the option's value → run the assembled command.
+            Some(opt) => Some(CmdResult::Dispatch(format!("UCS {opt} {t}"))),
+        }
+    }
+
+    fn on_point(&mut self, pt: DVec3) -> CmdResult {
+        // A clicked point only makes sense for the Origin option; otherwise a
+        // stray click is ignored (keep waiting for the typed keyword / value).
+        if matches!(self.option.as_deref(), Some(o) if Self::takes_point(o)) {
+            let opt = self.option.take().unwrap_or_default();
+            return CmdResult::Dispatch(format!("UCS {opt} {},{},{}", pt.x, pt.y, pt.z));
+        }
+        CmdResult::NeedPoint
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        match self.option.take() {
+            // No option chosen yet → behave like bare `UCS` (list).
+            None => CmdResult::Dispatch("UCS LIST".into()),
+            // Option chosen but no value supplied → cancel cleanly.
+            Some(_) => CmdResult::Cancel,
+        }
+    }
+}