diff --git a/crates/procnote-core/src/event/log.rs b/crates/procnote-core/src/event/log.rs
index 14cc6d0..f6fea80 100644
--- a/crates/procnote-core/src/event/log.rs
+++ b/crates/procnote-core/src/event/log.rs
@@ -263,6 +263,14 @@ mod tests {
                 content_type: "image/jpeg".to_string(),
                 sha256: "abc123".to_string(),
             },
+            Event::StepContentUpdated {
+                at: now,
+                execution_id: id,
+                step_heading: "Step 1".to_string(),
+                content: vec![StepContent::Prose {
+                    text: "Updated description".to_string(),
+                }],
+            },
         ];
 
         // Round-trip all event types through JSON.
diff --git a/crates/procnote-core/src/event/types.rs b/crates/procnote-core/src/event/types.rs
index e62864d..0946181 100644
--- a/crates/procnote-core/src/event/types.rs
+++ b/crates/procnote-core/src/event/types.rs
@@ -109,6 +109,14 @@ pub enum Event {
         sha256: String,
     },
 
+    // -- Step Content --
+    StepContentUpdated {
+        at: DateTime<Utc>,
+        execution_id: ExecutionId,
+        step_heading: String,
+        content: Vec<StepContent>,
+    },
+
     // -- Name --
     ExecutionRenamed {
         at: DateTime<Utc>,
@@ -161,6 +169,7 @@ impl Event {
             | Self::InputRecorded { .. }
             | Self::NoteAdded { .. }
             | Self::AttachmentAdded { .. }
+            | Self::StepContentUpdated { .. }
             | Self::ExecutionRenamed { .. } => Revertibility::Revertible,
 
             // Revert marker — not revertible
@@ -237,6 +246,9 @@ impl Event {
             } => {
                 format!("Recorded {label} = {filename} in {step_heading}")
             }
+            Self::StepContentUpdated { step_heading, .. } => {
+                format!("Updated content of step: {step_heading}")
+            }
             Self::ExecutionRenamed { name, .. } => {
                 format!("Renamed execution to: {name}")
             }
diff --git a/crates/procnote-core/src/execution/engine.rs b/crates/procnote-core/src/execution/engine.rs
index 880ef17..a27e4be 100644
--- a/crates/procnote-core/src/execution/engine.rs
+++ b/crates/procnote-core/src/execution/engine.rs
@@ -321,6 +321,16 @@ impl ExecutionState {
                 );
             }
 
+            Event::StepContentUpdated {
+                step_heading,
+                content,
+                ..
+            } => {
+                self.require_active()?;
+                let step = self.get_step_mut(step_heading)?;
+                step.content.clone_from(content);
+            }
+
             Event::ExecutionRenamed { name, .. } => {
                 if self.execution_id.is_none() {
                     return Err(ExecutionError::NotStarted);
@@ -419,6 +429,23 @@ impl ExecutionState {
         Ok(event)
     }
 
+    /// Update the content of an existing step.
+    pub fn update_step_content(
+        &mut self,
+        step_heading: &str,
+        content: Vec<StepContent>,
+    ) -> Result<Event, ExecutionError> {
+        self.require_active()?;
+        let event = Event::StepContentUpdated {
+            at: Utc::now(),
+            execution_id: self.require_execution_id()?,
+            step_heading: step_heading.to_string(),
+            content,
+        };
+        self.apply(&event)?;
+        Ok(event)
+    }
+
     /// Start a step.
     pub fn start_step(&mut self, heading: &str) -> Result<Event, ExecutionError> {
         self.require_active()?;
@@ -1234,4 +1261,148 @@ mod tests {
                 .contains_key("Current")
         );
     }
+
+    // -- StepContentUpdated tests --
+
+    #[test]
+    fn test_update_step_content() {
+        let template = sample_template();
+        let mut state = ExecutionState::new();
+        state.start(&template).unwrap();
+
+        let new_content = vec![StepContent::Prose {
+            text: "Updated description".to_string(),
+        }];
+        state
+            .update_step_content("Preconditions", new_content)
+            .unwrap();
+
+        assert_eq!(state.steps["Preconditions"].content.len(), 1);
+        assert!(
+            matches!(&state.steps["Preconditions"].content[0], StepContent::Prose { text } if text == "Updated description")
+        );
+    }
+
+    #[test]
+    fn test_update_step_content_preserves_inputs_and_notes() {
+        let template = sample_template();
+        let mut state = ExecutionState::new();
+        state.start(&template).unwrap();
+        state.start_step("Preconditions").unwrap();
+        state
+            .record_input("Preconditions", "Voltage", "5.0", Some("V"))
+            .unwrap();
+        state
+            .add_note("Some observation", Some("Preconditions"))
+            .unwrap();
+
+        let new_content = vec![StepContent::Prose {
+            text: "New prose".to_string(),
+        }];
+        state
+            .update_step_content("Preconditions", new_content)
+            .unwrap();
+
+        // Content is replaced.
+        assert_eq!(state.steps["Preconditions"].content.len(), 1);
+        // Inputs and notes are untouched.
+        assert_eq!(state.steps["Preconditions"].inputs["Voltage"].value, "5.0");
+        assert_eq!(state.steps["Preconditions"].notes.len(), 1);
+        assert_eq!(state.steps["Preconditions"].notes[0], "Some observation");
+    }
+
+    #[test]
+    fn test_cannot_update_content_before_start() {
+        let mut state = ExecutionState::new();
+        let result = state.update_step_content("Step 1", vec![]);
+        assert_eq!(result.unwrap_err(), ExecutionError::NotStarted);
+    }
+
+    #[test]
+    fn test_cannot_update_content_after_finish() {
+        let template = sample_template();
+        let mut state = ExecutionState::new();
+        state.start(&template).unwrap();
+        state.complete(CompletionStatus::Pass).unwrap();
+
+        let result = state.update_step_content("Preconditions", vec![]);
+        assert_eq!(result.unwrap_err(), ExecutionError::AlreadyFinished);
+    }
+
+    #[test]
+    fn test_cannot_update_content_nonexistent_step() {
+        let template = sample_template();
+        let mut state = ExecutionState::new();
+        state.start(&template).unwrap();
+
+        let result = state.update_step_content("Nonexistent Step", vec![]);
+        assert_eq!(
+            result.unwrap_err(),
+            ExecutionError::StepNotFound("Nonexistent Step".to_string())
+        );
+    }
+
+    #[test]
+    fn test_revert_step_content_updated() {
+        let template = sample_template();
+        let mut state = ExecutionState::new();
+        let mut events: Vec<Event> = Vec::new();
+        events.extend(state.start(&template).unwrap());
+        // index 0..4: ExecutionStarted + ExecutionRenamed + 3 StepAdded
+
+        let original_content = state.steps["Preconditions"].content.clone();
+
+        events.push(
+            state
+                .update_step_content(
+                    "Preconditions",
+                    vec![StepContent::Prose {
+                        text: "Changed".to_string(),
+                    }],
+                )
+                .unwrap(),
+        ); // index 5
+
+        // Revert the content update.
+        let revert = ExecutionState::revert_event(&events, 5, "undo edit").unwrap();
+        events.push(revert);
+
+        let rebuilt = ExecutionState::from_events(&events).unwrap();
+        assert_eq!(rebuilt.steps["Preconditions"].content, original_content);
+    }
+
+    #[test]
+    fn test_update_step_content_replay() {
+        let template = sample_template();
+        let mut state = ExecutionState::new();
+        let mut events: Vec<Event> = Vec::new();
+        events.extend(state.start(&template).unwrap());
+
+        events.push(
+            state
+                .update_step_content(
+                    "Preconditions",
+                    vec![StepContent::Prose {
+                        text: "Updated via replay".to_string(),
+                    }],
+                )
+                .unwrap(),
+        );
+
+        // Serialize and deserialize all events.
+        let jsons: Vec<String> = events
+            .iter()
+            .map(|e| serde_json::to_string(e).unwrap())
+            .collect();
+        let deserialized_events: Vec<Event> = jsons
+            .iter()
+            .map(|j| serde_json::from_str(j).unwrap())
+            .collect();
+
+        let replayed = ExecutionState::from_events(&deserialized_events).unwrap();
+        assert_eq!(replayed.steps["Preconditions"].content.len(), 1);
+        assert!(
+            matches!(&replayed.steps["Preconditions"].content[0], StepContent::Prose { text } if text == "Updated via replay")
+        );
+    }
 }
diff --git a/src-tauri/src/commands/execution.rs b/src-tauri/src/commands/execution.rs
index 0917599..461ba1f 100644
--- a/src-tauri/src/commands/execution.rs
+++ b/src-tauri/src/commands/execution.rs
@@ -368,7 +368,8 @@ fn event_step_and_label(event: &Event) -> (Option<String>, Option<String>) {
         Event::StepStarted { step_heading, .. }
         | Event::StepCompleted { step_heading, .. }
         | Event::StepSkipped { step_heading, .. }
-        | Event::CheckboxToggled { step_heading, .. } => (Some(step_heading.clone()), None),
+        | Event::CheckboxToggled { step_heading, .. }
+        | Event::StepContentUpdated { step_heading, .. } => (Some(step_heading.clone()), None),
         Event::InputRecorded {
             step_heading,
             label,
@@ -397,6 +398,7 @@ fn event_type_string(event: &Event) -> String {
         Event::InputRecorded { .. } => "input_recorded",
         Event::NoteAdded { .. } => "note_added",
         Event::AttachmentAdded { .. } => "attachment_added",
+        Event::StepContentUpdated { .. } => "step_content_updated",
         Event::ExecutionRenamed { .. } => "execution_renamed",
         Event::EventReverted { .. } => "event_reverted",
     }
@@ -416,6 +418,7 @@ fn event_at(event: &Event) -> String {
         | Event::InputRecorded { at, .. }
         | Event::NoteAdded { at, .. }
         | Event::AttachmentAdded { at, .. }
+        | Event::StepContentUpdated { at, .. }
         | Event::ExecutionRenamed { at, .. }
         | Event::EventReverted { at, .. } => at.to_rfc3339(),
     }
@@ -557,6 +560,10 @@ pub enum ExecutionAction {
         #[ts(optional)]
         after_step: Option<String>,
     },
+    UpdateStepContent {
+        step_heading: String,
+        content: Vec<StepContent>,
+    },
     AddAttachment {
         step_heading: String,
         label: String,
@@ -652,6 +659,12 @@ pub fn record_action(
         } => exec_state
             .add_step(&heading, content, after_step.as_deref())
             .map_err(|e| e.to_string())?,
+        ExecutionAction::UpdateStepContent {
+            step_heading,
+            content,
+        } => exec_state
+            .update_step_content(&step_heading, content)
+            .map_err(|e| e.to_string())?,
         ExecutionAction::AddAttachment {
             step_heading,
             label,
diff --git a/src/lib/components/EditStepDialog.svelte b/src/lib/components/EditStepDialog.svelte
new file mode 100644
index 0000000..faa1fd2
--- /dev/null
+++ b/src/lib/components/EditStepDialog.svelte
@@ -0,0 +1,184 @@
+<script lang="ts">
+    import type { StepSummary, StepContent } from "$lib/types";
+
+    let {
+        stepSummary,
+        onconfirm,
+        oncancel,
+    }: {
+        stepSummary: StepSummary;
+        onconfirm: (stepHeading: string, content: StepContent[]) => void;
+        oncancel: () => void;
+    } = $props();
+
+    // Extract existing prose text from content blocks.
+    let initialProse = $derived(
+        stepSummary.content
+            .filter((b) => b.type === "Prose")
+            .map((b) => (b as { type: "Prose"; text: string }).text)
+            .join("\n\n"),
+    );
+
+    let description = $state("");
+
+    // Initialize description from current prose on mount.
+    $effect(() => {
+        description = initialProse;
+    });
+
+    function submit() {
+        // Rebuild content array: replace all Prose entries with a single new
+        // one (if non-empty), keep Checkbox and InputBlock items in place.
+        const newContent: StepContent[] = [];
+        let proseInserted = false;
+
+        for (const block of stepSummary.content) {
+            if (block.type === "Prose") {
+                // Insert new prose at the position of the first original Prose block.
+                if (!proseInserted && description.trim()) {
+                    newContent.push({ type: "Prose", text: description.trim() });
+                    proseInserted = true;
+                }
+                // Skip remaining original Prose blocks (replaced by the single new one).
+            } else if (block.type === "Checkbox") {
+                newContent.push({
+                    type: "Checkbox",
+                    text: block.text,
+                    checked: block.checked,
+                });
+            } else if (block.type === "InputBlock") {
+                newContent.push({
+                    type: "InputBlock",
+                    inputs: block.inputs.map((i) => i.definition),
+                });
+            }
+        }
+
+        // If there were no Prose blocks originally but user typed something, append it.
+        if (!proseInserted && description.trim()) {
+            newContent.unshift({ type: "Prose", text: description.trim() });
+        }
+
+        onconfirm(stepSummary.heading, newContent);
+    }
+</script>
+
+<div class="modal-backdrop" role="presentation" onclick={oncancel}>
+    <!-- svelte-ignore a11y_click_events_have_key_events -->
+    <!-- svelte-ignore a11y_no_static_element_interactions -->
+    <div class="modal" onclick={(e) => e.stopPropagation()}>
+        <h3>Edit Step Content</h3>
+        <p class="hint">Edit the description for "{stepSummary.heading}".</p>
+        <label class="field">
+            <span class="field-label">Description</span>
+            <!-- svelte-ignore a11y_autofocus -->
+            <textarea
+                bind:value={description}
+                placeholder="Step description (Markdown supported)..."
+                rows="6"
+                autofocus
+            ></textarea>
+        </label>
+        <div class="modal-actions">
+            <button class="btn btn-secondary" onclick={oncancel}>Cancel</button>
+            <button class="btn btn-primary" onclick={submit}>Save</button>
+        </div>
+    </div>
+</div>
+
+<style>
+    .modal-backdrop {
+        position: fixed;
+        inset: 0;
+        background: rgba(0, 0, 0, 0.4);
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        z-index: 100;
+    }
+
+    .modal {
+        background: #fff;
+        border-radius: 8px;
+        padding: 24px;
+        min-width: 400px;
+        max-width: 520px;
+        box-shadow: 0 8px 32px rgba(0, 0, 0, 0.2);
+    }
+
+    .modal h3 {
+        margin: 0 0 4px;
+        font-size: 16px;
+    }
+
+    .hint {
+        margin: 0 0 16px;
+        font-size: 13px;
+        color: #888;
+    }
+
+    .field {
+        display: block;
+        margin-bottom: 12px;
+    }
+
+    .field-label {
+        display: block;
+        font-size: 12px;
+        font-weight: 600;
+        margin-bottom: 4px;
+        color: #555;
+    }
+
+    .field textarea {
+        width: 100%;
+        padding: 8px 10px;
+        border: 1px solid #ccc;
+        border-radius: 4px;
+        font: inherit;
+        font-size: 13px;
+        resize: vertical;
+    }
+
+    .field textarea:focus {
+        outline: none;
+        border-color: #1a1a2e;
+        box-shadow: 0 0 0 2px rgba(26, 26, 46, 0.15);
+    }
+
+    .modal-actions {
+        display: flex;
+        justify-content: flex-end;
+        gap: 8px;
+        margin-top: 16px;
+    }
+
+    .btn {
+        padding: 8px 16px;
+        border-radius: 4px;
+        font: inherit;
+        font-size: 13px;
+        font-weight: 600;
+        cursor: pointer;
+        border: 1px solid transparent;
+    }
+
+    .btn-primary {
+        background: #1a1a2e;
+        color: #fff;
+    }
+
+    .btn-primary:hover {
+        background: #16213e;
+    }
+
+    .btn-secondary {
+        background: #fff;
+        color: #333;
+        border-color: #ccc;
+    }
+
+    .btn-secondary:hover {
+        background: #f5f5f5;
+    }
+</style>
diff --git a/src/lib/components/StepCard.svelte b/src/lib/components/StepCard.svelte
index 0644b77..2c3c477 100644
--- a/src/lib/components/StepCard.svelte
+++ b/src/lib/components/StepCard.svelte
@@ -39,10 +39,11 @@
 
     import "highlight.js/styles/atom-one-light.css";
 
-    import type { StepSummary, EventHistoryEntry } from "$lib/types";
+    import type { StepSummary, StepContent, EventHistoryEntry } from "$lib/types";
     import { formatTimestamp } from "$lib/utils/format";
     import AttachmentField from "./AttachmentField.svelte";
     import CheckboxItem from "./CheckboxItem.svelte";
+    import EditStepDialog from "./EditStepDialog.svelte";
     import InputField from "./InputField.svelte";
     import NoteEditor from "./NoteEditor.svelte";
 
@@ -82,6 +83,7 @@
 
     let showSkipDialog = $state(false);
     let skipReason = $state("");
+    let showEditDialog = $state(false);
 
     // Find the most recent revertible step-status event (complete/skip/start).
     let revertibleStatusEvent = $derived(
@@ -174,6 +176,15 @@
             step_heading: stepSummary.heading,
         });
     }
+
+    function updateContent(stepHeading: string, content: StepContent[]) {
+        onaction({
+            action: "update_step_content",
+            step_heading: stepHeading,
+            content,
+        });
+        showEditDialog = false;
+    }
 </script>
 
 <div
@@ -186,6 +197,9 @@
     <div class="step-header">
         <div class="step-status-indicator"></div>
         <h3 class="step-heading">{stepSummary.heading}</h3>
+        {#if executionActive}
+            <button class="btn-edit" onclick={() => (showEditDialog = true)}>Edit</button>
+        {/if}
         {#if stepSummary.status_at}
             <span class="timestamp">{formatTimestamp(stepSummary.status_at)}</span>
         {/if}
@@ -324,6 +338,14 @@
     {/if}
 </div>
 
+{#if showEditDialog}
+    <EditStepDialog
+        {stepSummary}
+        onconfirm={updateContent}
+        oncancel={() => (showEditDialog = false)}
+    />
+{/if}
+
 <style>
     .step-card {
         background: #fff;
@@ -392,6 +414,22 @@
         font-weight: 600;
     }
 
+    .btn-edit {
+        padding: 2px 8px;
+        border: 1px solid #ccc;
+        border-radius: 3px;
+        background: #fff;
+        color: #666;
+        font: inherit;
+        font-size: 11px;
+        cursor: pointer;
+    }
+
+    .btn-edit:hover {
+        background: #f5f5f5;
+        color: #333;
+    }
+
     .step-description {
         margin: 0 0 4px;
         font-size: 14px;
diff --git a/src/lib/types/generated/ExecutionAction.ts b/src/lib/types/generated/ExecutionAction.ts
index aaffc8d..16cd114 100644
--- a/src/lib/types/generated/ExecutionAction.ts
+++ b/src/lib/types/generated/ExecutionAction.ts
@@ -5,4 +5,4 @@ import type { StepContent } from "./StepContent";
 /**
  * Action payload from the frontend for recording events.
  */
-export type ExecutionAction = { "action": "start_step", step_heading: string, } | { "action": "complete_step", step_heading: string, } | { "action": "skip_step", step_heading: string, reason: string, } | { "action": "toggle_checkbox", step_heading: string, text: string, checked: boolean, } | { "action": "record_input", step_heading: string, label: string, value: string, unit?: string, } | { "action": "add_note", text: string, step_heading?: string, } | { "action": "add_step", heading: string, content: Array<StepContent>, after_step?: string, } | { "action": "add_attachment", step_heading: string, label: string, filename: string, path: string, content_type: string, } | { "action": "complete", status: CompletionStatus, } | { "action": "abort", reason: string, } | { "action": "rename_execution", name: string, } | { "action": "revert_event", event_index: number, reason: string, };
+export type ExecutionAction = { "action": "start_step", step_heading: string, } | { "action": "complete_step", step_heading: string, } | { "action": "skip_step", step_heading: string, reason: string, } | { "action": "toggle_checkbox", step_heading: string, text: string, checked: boolean, } | { "action": "record_input", step_heading: string, label: string, value: string, unit?: string, } | { "action": "add_note", text: string, step_heading?: string, } | { "action": "add_step", heading: string, content: Array<StepContent>, after_step?: string, } | { "action": "update_step_content", step_heading: string, content: Array<StepContent>, } | { "action": "add_attachment", step_heading: string, label: string, filename: string, path: string, content_type: string, } | { "action": "complete", status: CompletionStatus, } | { "action": "abort", reason: string, } | { "action": "rename_execution", name: string, } | { "action": "revert_event", event_index: number, reason: string, };