diff --git a/docs/PARITY_CHECKLIST.md b/docs/PARITY_CHECKLIST.md
index d44b2e1..d4c9f11 100644
--- a/docs/PARITY_CHECKLIST.md
+++ b/docs/PARITY_CHECKLIST.md
@@ -67,6 +67,28 @@ Closed by the `feat/columns-panel` parity work (2026-08-13):
 | Constants / tags (save/list/delete) | 🔤 Save as constant + picker | `logan_constants` (`/api/constants-*`) | ✅ shared `constantsStore` |
 | Column Layouts (save/list/delete) | Column Layouts builder / Columns window | `logan_column_layouts` (`/api/column-layout-*`) | ✅ shared `columnLayoutsStore` |
 
+Uniform entity `description` (2026-08-13) — every saveable "basic entity" gained an
+optional `description?: string` so both operators can record an entity's purpose/why
+(naming matches the existing `BaselineRecord.description` / `InvestigationTemplate.description`;
+findings already carry `detail`). Human editing = a shared `editEntityDescription()` helper
+(prefilled modal; blank clears) reached by right-click on the entity's chip/row, plus a `📝`
+marker + the note in the hover tooltip. Agent editing = a `description` param on the entities
+that have an MCP create/save tool. ONE field name, both operators (rule 5).
+
+| Entity | Human sets it | AI sets it | Status |
+|--------|---------------|-----------|--------|
+| Constant / tag | Right-click in the constants picker | `logan_constants` `description` (`/api/constants-save`) | ✅ both |
+| Bookmark | Right-click a bookmark row | `logan_add_bookmark` `description` (`/api/bookmark`, `-update`) | ✅ both |
+| Highlight | Right-click a highlight row | `logan_highlight` `description` (`/api/highlight`, `-update`) | ✅ both |
+| Column Layout | Right-click a layout chip | `logan_column_layouts` layout.`description` (`/api/column-layout-save`) | ✅ both |
+| Search config | Chip context menu → "Edit description" | — (no MCP create tool) | ✅ human · field carried for AI |
+| Search config session | Chip context menu → "Edit description" | — (no MCP create tool) | ✅ human · field carried for AI |
+| Pattern property (trend) | Right-click a property chip | — (no MCP create tool) | ✅ human · field carried for AI |
+
+(Search configs / sessions / pattern-properties have no MCP *create* tool today — a
+pre-existing human-only exemption — so their `description` is human-set; the field is
+carried on the type so an AI tool added later inherits it for free.)
+
 Still human-only — deliberate backlog (add a counterpart or a written exemption
 when each is next touched):
 
diff --git a/src/main/api-server.ts b/src/main/api-server.ts
index ed4b1e3..b52e238 100644
--- a/src/main/api-server.ts
+++ b/src/main/api-server.ts
@@ -865,7 +865,8 @@ export function startApiServer(ctx: ApiContext): void {
           const name = String(body.name || '').trim();
           const value = String(body.value ?? '');
           if (!name || !value) { sendJson(res, { success: false, error: 'name and value are required' }); return; }
-          saveConstant(name, value);
+          const description = typeof body.description === 'string' ? body.description : undefined;
+          saveConstant(name, value, undefined, description);
           sendJson(res, { success: true, entries: getConstants() });
           return;
         }
@@ -910,6 +911,7 @@ export function startApiServer(ctx: ApiContext): void {
             label: body.label || '',
             color: body.color || '#ffff00',
             lineText: body.lineText,
+            ...(typeof body.description === 'string' ? { description: body.description } : {}),
           };
           const result = ctx.addBookmark(bookmark);
           sendJson(res, result);
@@ -927,6 +929,7 @@ export function startApiServer(ctx: ApiContext): void {
             includeWhitespace: body.includeWhitespace ?? false,
             highlightAll: body.highlightAll ?? true,
             isGlobal: body.isGlobal ?? false,
+            ...(typeof body.description === 'string' ? { description: body.description } : {}),
           };
           const result = ctx.addHighlight(highlight);
           sendJson(res, result);
@@ -948,6 +951,7 @@ export function startApiServer(ctx: ApiContext): void {
             ...existing,
             label: body.label ?? existing.label,
             color: body.color ?? existing.color,
+            description: body.description !== undefined ? body.description : existing.description,
           };
           const result = ctx.updateBookmark(updated);
           sendJson(res, result);
@@ -976,6 +980,7 @@ export function startApiServer(ctx: ApiContext): void {
             pattern: body.pattern ?? existing.pattern,
             backgroundColor: body.backgroundColor ?? existing.backgroundColor,
             textColor: body.textColor !== undefined ? body.textColor : existing.textColor,
+            description: body.description !== undefined ? body.description : existing.description,
           };
           const result = ctx.updateHighlight(updated);
           sendJson(res, result);
diff --git a/src/main/columnLayoutsStore.ts b/src/main/columnLayoutsStore.ts
index 94bb362..d04961a 100644
--- a/src/main/columnLayoutsStore.ts
+++ b/src/main/columnLayoutsStore.ts
@@ -14,6 +14,7 @@ export interface ColumnLayoutSaved {
   delimiterName?: string;
   pattern?: { regex: string; flags: string; fields: string[] };
   columns: Array<{ index: number; name?: string; visible: boolean }>;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 const LAYOUTS_PATH = (): string => path.join(os.homedir(), '.logan', 'column-layouts.json');
diff --git a/src/main/constantsStore.ts b/src/main/constantsStore.ts
index 509b8c2..ef43cd7 100644
--- a/src/main/constantsStore.ts
+++ b/src/main/constantsStore.ts
@@ -13,6 +13,7 @@ export interface ConstantEntry {
   value: string;
   createdAt: string; // ISO 8601
   updatedAt: string; // ISO 8601
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 export interface ConstantsStore {
@@ -84,7 +85,7 @@ export class ConstantsStoreImpl {
   }
 
   /** Upsert a named constant. Empty name/value is a no-op. Debounced write. */
-  save(name: string, value: string, at: number = Date.now()): void {
+  save(name: string, value: string, at: number = Date.now(), description?: string): void {
     try {
       const trimmedName = (name || '').trim();
       if (!trimmedName || !value) return;
@@ -94,8 +95,12 @@ export class ConstantsStoreImpl {
       if (existing) {
         existing.value = value;
         existing.updatedAt = iso;
+        if (description !== undefined) existing.description = description;
       } else {
-        store.entries[trimmedName] = { name: trimmedName, value, createdAt: iso, updatedAt: iso };
+        store.entries[trimmedName] = {
+          name: trimmedName, value, createdAt: iso, updatedAt: iso,
+          ...(description !== undefined ? { description } : {}),
+        };
       }
       store.updatedAt = iso;
       this.scheduleWrite();
@@ -150,8 +155,8 @@ function store(): ConstantsStoreImpl {
   return instance;
 }
 
-export function saveConstant(name: string, value: string, at?: number): void {
-  store().save(name, value, at);
+export function saveConstant(name: string, value: string, at?: number, description?: string): void {
+  store().save(name, value, at, description);
 }
 
 export function getConstants(): ConstantEntry[] {
diff --git a/src/main/index.ts b/src/main/index.ts
index f46aa5b..7653a7e 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -7806,8 +7806,8 @@ ipcMain.handle(IPC.COMPILE_PATTERN, (_, input: CompileInput) => {
 // ── Named constants IPC ────────────────────────────────────────────────
 // Captured from a selection via the log viewer's "Save as constant…" gesture.
 // Persistence-only this brick; a viewer/consumer brick lands later.
-ipcMain.handle(IPC.CONSTANTS_SAVE, (_, name: string, value: string) => {
-  saveConstant(name, value);
+ipcMain.handle(IPC.CONSTANTS_SAVE, (_, name: string, value: string, description?: string) => {
+  saveConstant(name, value, undefined, description);
   return { success: true };
 });
 
diff --git a/src/mcp-server/index.ts b/src/mcp-server/index.ts
index 9cdf97b..6bc1873 100644
--- a/src/mcp-server/index.ts
+++ b/src/mcp-server/index.ts
@@ -369,13 +369,14 @@ server.tool(
     action: z.enum(['list', 'save', 'delete']).describe('list all · save one · delete one'),
     name: z.string().optional().describe('constant name (required for save/delete)'),
     value: z.string().optional().describe('constant value (required for save)'),
+    description: z.string().optional().describe('optional note on what this constant is for / why (shown to the human too)'),
   },
-  async ({ action, name, value }) => {
+  async ({ action, name, value, description }) => {
     try {
       const path = action === 'save' ? '/api/constants-save'
         : action === 'delete' ? '/api/constants-delete'
         : '/api/constants-list';
-      const result = await apiCall('POST', path, { name, value });
+      const result = await apiCall('POST', path, { name, value, description });
       return { content: [{ type: 'text', text: JSON.stringify(result, null, 2) }] };
     } catch (err: any) {
       return { content: [{ type: 'text', text: `Error: ${err.message}` }], isError: true };
@@ -389,7 +390,7 @@ server.tool(
   'Manage saved Column Layouts (named column definitions — delimiter OR regex/paint pattern + per-column name/visibility) — the same store the human Column Layouts builder / Columns window uses. list · save · delete. (Applying a layout to the human viewer is human-only.)',
   {
     action: z.enum(['list', 'save', 'delete']).describe('list all · save one · delete one'),
-    layout: z.any().optional().describe('layout object for save: {id, name, method:"delimiter"|"pattern", delimiter?/pattern?, columns:[{index,name?,visible}]}'),
+    layout: z.any().optional().describe('layout object for save: {id, name, method:"delimiter"|"pattern", delimiter?/pattern?, columns:[{index,name?,visible}], description?}. Include an optional `description` note on what the layout is for.'),
     id: z.string().optional().describe('layout id (required for delete)'),
   },
   async ({ action, layout, id }) => {
@@ -429,10 +430,11 @@ server.tool(
     lineNumber: z.number().int().min(0).describe('0-based line number to bookmark'),
     label: z.string().default('').describe('Optional label/note for the bookmark'),
     color: z.string().default('#ffff00').describe('Bookmark color (hex)'),
+    description: z.string().optional().describe('optional note on why this line matters / what to check (shown to the human too)'),
   },
-  async ({ lineNumber, label, color }) => {
+  async ({ lineNumber, label, color, description }) => {
     try {
-      const result = await apiCall('POST', '/api/bookmark', { lineNumber, label, color });
+      const result = await apiCall('POST', '/api/bookmark', { lineNumber, label, color, description });
       return { content: [{ type: 'text', text: JSON.stringify(result, null, 2) }] };
     } catch (err: any) {
       return { content: [{ type: 'text', text: `Error: ${err.message}` }], isError: true };
@@ -468,10 +470,11 @@ server.tool(
     matchCase: z.boolean().default(false).describe('Case-sensitive matching'),
     backgroundColor: z.string().default('#ffff00').describe('Highlight background color (hex)'),
     isGlobal: z.boolean().default(false).describe('Apply to all files (true) or current file only (false)'),
+    description: z.string().optional().describe('optional note on what this highlight is for / why (shown to the human too)'),
   },
-  async ({ pattern, isRegex, matchCase, backgroundColor, isGlobal }) => {
+  async ({ pattern, isRegex, matchCase, backgroundColor, isGlobal, description }) => {
     try {
-      const result = await apiCall('POST', '/api/highlight', { pattern, isRegex, matchCase, backgroundColor, isGlobal });
+      const result = await apiCall('POST', '/api/highlight', { pattern, isRegex, matchCase, backgroundColor, isGlobal, description });
       return { content: [{ type: 'text', text: JSON.stringify(result, null, 2) }] };
     } catch (err: any) {
       return { content: [{ type: 'text', text: `Error: ${err.message}` }], isError: true };
diff --git a/src/preload/index.ts b/src/preload/index.ts
index 3f71fe1..5c7c8d3 100644
--- a/src/preload/index.ts
+++ b/src/preload/index.ts
@@ -971,8 +971,8 @@ const api = {
     ipcRenderer.invoke(IPC.COMPILE_PATTERN, input),
 
   // Named constants (captured from a selection via "Save as constant…")
-  saveConstant: (name: string, value: string): Promise<{ success: boolean; error?: string }> =>
-    ipcRenderer.invoke(IPC.CONSTANTS_SAVE, name, value),
+  saveConstant: (name: string, value: string, description?: string): Promise<{ success: boolean; error?: string }> =>
+    ipcRenderer.invoke(IPC.CONSTANTS_SAVE, name, value, description),
   getConstants: (): Promise<{ success: boolean; entries?: any[] }> =>
     ipcRenderer.invoke(IPC.CONSTANTS_GET),
   deleteConstant: (name: string): Promise<{ success: boolean; removed?: boolean }> =>
diff --git a/src/renderer/renderer.ts b/src/renderer/renderer.ts
index 25552f0..4e0b708 100644
--- a/src/renderer/renderer.ts
+++ b/src/renderer/renderer.ts
@@ -7305,11 +7305,20 @@ function renderTrendPropChips(): void {
   for (const prop of trendPatternProperties) {
     const chip = document.createElement('span');
     chip.className = 'trend-prop-chip';
-    chip.title = `/${prop.pattern}/${prop.patternFlags || ''}  — click to chart with the selected cell type`;
+    chip.title = `/${prop.pattern}/${prop.patternFlags || ''}  — click to chart with the selected cell type` + descTitleSuffix(prop.description);
+    // Right-click → add/edit its description (purpose/why).
+    chip.addEventListener('contextmenu', (e) => {
+      e.preventDefault();
+      void editEntityDescription(prop.description, async (d) => {
+        prop.description = d || undefined;
+        await window.api.patternPropSave(prop);
+        renderTrendPropChips();
+      });
+    });
 
     const name = document.createElement('button');
     name.className = 'trend-prop-name';
-    name.textContent = prop.name;
+    name.textContent = prop.description ? `📝 ${prop.name}` : prop.name;
     name.addEventListener('click', () => applyTrendProperty(prop));
 
     const del = document.createElement('button');
@@ -12521,7 +12530,8 @@ function renderSearchConfigsChips(): void {
     const patternText = document.createElement('span');
     patternText.className = 'sc-chip-pattern';
     patternText.textContent = config.pattern;
-    patternText.title = config.pattern;
+    patternText.title = config.pattern + descTitleSuffix(config.description);
+    if (config.description) patternText.textContent = `📝 ${config.pattern}`;
 
     const count = document.createElement('span');
     count.className = 'sc-chip-count';
@@ -13775,6 +13785,18 @@ function showSearchConfigContextMenu(e: MouseEvent, config: SearchConfigDef): vo
     showSearchConfigForm(config.id);
   });
 
+  const descItem = document.createElement('button');
+  descItem.className = 'sc-context-menu-item';
+  descItem.textContent = config.description ? 'Edit description…' : 'Add description…';
+  descItem.addEventListener('click', () => {
+    menu.remove();
+    void editEntityDescription(config.description, async (d) => {
+      config.description = d || undefined;
+      await window.api.searchConfigSave(config);
+      renderSearchConfigsChips();
+    });
+  });
+
   const exportItem = document.createElement('button');
   exportItem.className = 'sc-context-menu-item';
   exportItem.textContent = 'Export Results';
@@ -13798,6 +13820,7 @@ function showSearchConfigContextMenu(e: MouseEvent, config: SearchConfigDef): vo
   });
 
   menu.appendChild(editItem);
+  menu.appendChild(descItem);
   menu.appendChild(exportItem);
   menu.appendChild(deleteItem);
   document.body.appendChild(menu);
@@ -14552,13 +14575,14 @@ function renderSearchConfigSessionsUI(): void {
     chip.className = `sc-session-chip${isActive ? ' active' : ''}`;
     chip.dataset.id = session.id;
     const scopeTag = session.isGlobal ? ' [Global]' : ' [Local]';
-    chip.title = isActive
+    chip.title = (isActive
       ? `${escapeHtml(session.name)} — applied. Click to deselect (clear its search configs).`
-      : `${escapeHtml(session.name)} (${session.configs.length} configs)${scopeTag} — click to apply`;
+      : `${escapeHtml(session.name)} (${session.configs.length} configs)${scopeTag} — click to apply`)
+      + descTitleSuffix(session.description);
 
     const nameSpan = document.createElement('span');
     nameSpan.className = 'sc-session-chip-name';
-    nameSpan.textContent = session.name;
+    nameSpan.textContent = session.description ? `📝 ${session.name}` : session.name;
 
     const badge = document.createElement('span');
     badge.className = 'sc-session-chip-badge';
@@ -14709,6 +14733,18 @@ function showSearchConfigSessionContextMenu(e: MouseEvent, session: SearchConfig
     }
   });
 
+  const descItem = document.createElement('button');
+  descItem.className = 'sc-context-menu-item';
+  descItem.textContent = session.description ? 'Edit description…' : 'Add description…';
+  descItem.addEventListener('click', () => {
+    menu.remove();
+    void editEntityDescription(session.description, async (d) => {
+      session.description = d || undefined;
+      await window.api.searchConfigSessionSave(session);
+      renderSearchConfigSessionsUI();
+    });
+  });
+
   // Promote/demote scope so an existing session can be made reusable across files
   // (or pinned back to this file) without re-saving.
   const scopeItem = document.createElement('button');
@@ -14723,6 +14759,7 @@ function showSearchConfigSessionContextMenu(e: MouseEvent, session: SearchConfig
   });
 
   menu.appendChild(renameItem);
+  menu.appendChild(descItem);
   menu.appendChild(scopeItem);
   menu.appendChild(deleteItem);
   document.body.appendChild(menu);
@@ -16968,13 +17005,25 @@ function renderColumnLayoutChips(): void {
     return;
   }
   el.innerHTML = columnLayouts.map((l: any) =>
-    `<span class="patcol-chip" data-id="${escapeHtml(l.id)}"><span class="patcol-chip-name" title="${escapeHtml(l.delimiterName || l.delimiter || '')} · ${(l.columns || []).length} cols">${escapeHtml(l.name)}</span><button class="patcol-chip-x" data-id="${escapeHtml(l.id)}" title="Delete layout">×</button></span>`
+    `<span class="patcol-chip" data-id="${escapeHtml(l.id)}"><span class="patcol-chip-name" title="${escapeHtml(l.delimiterName || l.delimiter || '')} · ${(l.columns || []).length} cols${l.description ? '\n📝 ' + escapeHtml(l.description) : ''}">${l.description ? '📝 ' : ''}${escapeHtml(l.name)}</span><button class="patcol-chip-x" data-id="${escapeHtml(l.id)}" title="Delete layout">×</button></span>`
   ).join('');
   el.querySelectorAll('.patcol-chip-name').forEach((b) => b.addEventListener('click', (e) => {
     const id = ((e.currentTarget as HTMLElement).closest('.patcol-chip') as HTMLElement)?.dataset.id;
     const layout = columnLayouts.find((l: any) => l.id === id);
     if (layout) applyColumnLayoutToModal(layout);
   }));
+  // Right-click a layout chip → add/edit its description (purpose/why).
+  el.querySelectorAll('.patcol-chip').forEach((chip) => chip.addEventListener('contextmenu', (e) => {
+    e.preventDefault();
+    const id = (chip as HTMLElement).dataset.id;
+    const layout = columnLayouts.find((l: any) => l.id === id);
+    if (!layout) return;
+    void editEntityDescription(layout.description, async (d) => {
+      layout.description = d || undefined;
+      await (window.api as any).columnLayoutSave(layout);
+      renderColumnLayoutChips();
+    });
+  }));
   el.querySelectorAll('.patcol-chip-x').forEach((b) => b.addEventListener('click', async (e) => {
     e.stopPropagation();
     const id = (e.currentTarget as HTMLElement).dataset.id;
@@ -17069,7 +17118,7 @@ function applyColumnPattern(
 // include list. onPick(value, name) fires on choose; each row has a × to delete.
 async function showConstantsPickerMenu(anchor: HTMLElement, onPick: (value: string, name: string) => void): Promise<void> {
   document.getElementById('constants-picker-menu')?.remove();
-  let entries: Array<{ name: string; value: string }> = [];
+  let entries: Array<{ name: string; value: string; description?: string }> = [];
   try {
     const res = await window.api.getConstants();
     entries = (res && res.entries) || [];
@@ -17081,8 +17130,8 @@ async function showConstantsPickerMenu(anchor: HTMLElement, onPick: (value: stri
   menu.innerHTML = entries.length === 0
     ? '<div class="context-menu-item disabled">No constants yet — right-click a selection → “🔤 Save as constant”.</div>'
     : entries.map(e =>
-        `<div class="context-menu-item constant-row" data-value="${escapeHtml(e.value)}" data-name="${escapeHtml(e.name)}">` +
-        `<span class="constant-name">${escapeHtml(e.name)}</span>` +
+        `<div class="context-menu-item constant-row" data-value="${escapeHtml(e.value)}" data-name="${escapeHtml(e.name)}" title="${escapeHtml((e.description ? '📝 ' + e.description + '\n' : '') + 'click to use · right-click to edit description')}">` +
+        `<span class="constant-name">${e.description ? '📝 ' : ''}${escapeHtml(e.name)}</span>` +
         `<span class="constant-value">${escapeHtml(e.value.length > 40 ? e.value.slice(0, 37) + '…' : e.value)}</span>` +
         `<button class="constant-del" data-name="${escapeHtml(e.name)}" title="Delete constant">×</button></div>`
       ).join('');
@@ -17103,6 +17152,17 @@ async function showConstantsPickerMenu(anchor: HTMLElement, onPick: (value: stri
       onPick(row.dataset.value || '', row.dataset.name || '');
       close();
     });
+    // Right-click → add/edit this constant's description (purpose/why).
+    row.addEventListener('contextmenu', (e) => {
+      e.preventDefault();
+      const name = row.dataset.name || '';
+      const value = row.dataset.value || '';
+      const current = entries.find(en => en.name === name)?.description;
+      close();
+      void editEntityDescription(current, async (d) => {
+        await window.api.saveConstant(name, value, d);
+      });
+    });
   });
   menu.querySelectorAll<HTMLElement>('.constant-del').forEach(btn => {
     btn.addEventListener('click', async (e) => {
@@ -20147,7 +20207,7 @@ function updateBookmarksUI(): void {
           ? `<span class="bookmark-color-dot" style="background:${b.color}"></span>`
           : '';
         return `
-      <div class="bookmark-item" data-id="${b.id}" data-line="${b.lineNumber}" title="${b.lineText ? escapeHtml(b.lineText) : (b.label ? escapeHtml(b.label) : 'Click to go to line, double-click to edit')}">
+      <div class="bookmark-item" data-id="${b.id}" data-line="${b.lineNumber}" title="${(b.lineText ? escapeHtml(b.lineText) : (b.label ? escapeHtml(b.label) : 'Click to go to line, double-click to edit')) + escapeHtml(descTitleSuffix(b.description))}">
         <div class="bookmark-info">
           ${colorDot}<span class="bookmark-line">Line ${b.lineNumber + 1}</span>
           ${b.lineText ? `<span class="bookmark-text">${escapeHtml(b.lineText.substring(0, 120))}</span>` : ''}
@@ -20184,6 +20244,19 @@ function updateBookmarksUI(): void {
       const id = (item as HTMLElement).dataset.id!;
       editBookmarkComment(id);
     });
+
+    // Right-click → add/edit its description (purpose/why), distinct from the label.
+    item.addEventListener('contextmenu', (e) => {
+      e.preventDefault();
+      const id = (item as HTMLElement).dataset.id!;
+      const bm = state.bookmarks.find((b) => b.id === id);
+      if (!bm) return;
+      void editEntityDescription(bm.description, async (d) => {
+        bm.description = d || undefined;
+        await window.api.updateBookmark(bm);
+        updateBookmarksUI();
+      });
+    });
   });
 }
 
@@ -20375,11 +20448,11 @@ function updateHighlightsUI(): void {
         const total = matches?.length ?? 0;
         const posText = total > 0 ? `${currentIdx + 1}/${total}` : '0/0';
         return `
-      <div class="highlight-item" data-id="${h.id}" title="${h.isGlobal ? 'Global - applies to all files' : 'Local - applies to this file only'}">
+      <div class="highlight-item" data-id="${h.id}" title="${(h.isGlobal ? 'Global - applies to all files' : 'Local - applies to this file only') + escapeHtml(descTitleSuffix(h.description))}">
         <div class="highlight-row">
           <span class="highlight-color" data-id="${h.id}" style="background-color: ${h.backgroundColor}" title="Click to change color"></span>
           <input type="color" class="highlight-color-picker" data-id="${h.id}" value="${h.backgroundColor}" style="display:none">
-          <span class="highlight-pattern">${escapeHtml(h.pattern)}</span>
+          <span class="highlight-pattern">${h.description ? '📝 ' : ''}${escapeHtml(h.pattern)}</span>
           <span class="highlight-scope ${h.isGlobal ? 'global' : 'local'}">${h.isGlobal ? 'G' : 'L'}</span>
           <div class="highlight-actions">
             <button class="highlight-toggle-global" data-id="${h.id}" title="${h.isGlobal ? 'Make local (this file only)' : 'Make global (all files)'}">${h.isGlobal ? '🌐' : '📄'}</button>
@@ -20416,6 +20489,21 @@ function updateHighlightsUI(): void {
     });
   });
 
+  // Right-click a highlight row → add/edit its description (purpose/why).
+  elements.highlightsList.querySelectorAll('.highlight-item').forEach((item) => {
+    item.addEventListener('contextmenu', (e) => {
+      e.preventDefault();
+      const id = (item as HTMLElement).dataset.id!;
+      const hl = state.highlights.find((h) => h.id === id);
+      if (!hl) return;
+      void editEntityDescription(hl.description, async (d) => {
+        hl.description = d || undefined;
+        await window.api.updateHighlight(hl);
+        updateHighlightsUI();
+      });
+    });
+  });
+
   // Add click handlers for toggle global
   elements.highlightsList.querySelectorAll('.highlight-toggle-global').forEach((btn) => {
     btn.addEventListener('click', async (e) => {
@@ -23808,6 +23896,59 @@ async function applyHighlightGroup(groupId: string): Promise<void> {
   renderVisibleLines();
 }
 
+// ── Uniform "description" editor for saveable entities ─────────────────────────
+// Every saveable entity (tag/constant, search pattern, session, column layout,
+// bookmark, highlight, trend property) carries an optional `description`. This modal
+// PREFILLS the current text (unlike showTextInputModal's placeholder-only input) and
+// lets you save an empty string to CLEAR it. Returns the new text, or null if cancelled.
+function showDescriptionModal(current: string): Promise<string | null> {
+  return new Promise((resolve) => {
+    const overlay = document.createElement('div');
+    overlay.className = 'modal';
+    overlay.style.cssText = 'display:flex;align-items:center;justify-content:center;';
+    overlay.innerHTML = `
+      <div class="modal-content" style="width:440px;">
+        <div class="modal-header"><h3>Edit description</h3></div>
+        <div class="modal-body">
+          <div class="filter-group">
+            <label>Purpose / why (optional — blank clears it). ⌘/Ctrl+Enter to save.</label>
+            <textarea class="modal-input" rows="3" style="resize:vertical;width:100%;"></textarea>
+          </div>
+        </div>
+        <div class="modal-footer">
+          <button class="secondary-btn" data-action="cancel">Cancel</button>
+          <button class="primary-btn" data-action="save">Save</button>
+        </div>
+      </div>`;
+    const input = overlay.querySelector('textarea') as HTMLTextAreaElement;
+    input.value = current;
+    const close = (v: string | null) => { overlay.remove(); resolve(v); };
+    (overlay.querySelector('[data-action="save"]') as HTMLButtonElement).addEventListener('click', () => close(input.value.trim()));
+    (overlay.querySelector('[data-action="cancel"]') as HTMLButtonElement).addEventListener('click', () => close(null));
+    input.addEventListener('keydown', (e) => {
+      if (e.key === 'Enter' && (e.metaKey || e.ctrlKey)) close(input.value.trim());
+      else if (e.key === 'Escape') close(null);
+    });
+    overlay.addEventListener('click', (e) => { if (e.target === overlay) close(null); });
+    document.body.appendChild(overlay);
+    input.focus();
+    input.select();
+  });
+}
+
+// Prompt for a new description and persist via `save` (which receives '' to clear).
+async function editEntityDescription(current: string | undefined, save: (desc: string) => void | Promise<void>): Promise<void> {
+  const next = await showDescriptionModal(current || '');
+  if (next === null) return; // cancelled
+  await save(next);
+  showToast(next ? 'Description saved' : 'Description cleared');
+}
+
+// Tooltip suffix: append an entity's description to a title string when present.
+function descTitleSuffix(description?: string): string {
+  return description ? `\n📝 ${description}` : '';
+}
+
 function showTextInputModal(title: string, label: string, placeholder: string): Promise<string | null> {
   return new Promise((resolve) => {
     const overlay = document.createElement('div');
diff --git a/src/renderer/types.d.ts b/src/renderer/types.d.ts
index 4ef399c..01bc504 100644
--- a/src/renderer/types.d.ts
+++ b/src/renderer/types.d.ts
@@ -123,6 +123,7 @@ interface Bookmark {
   color?: string;
   lineText?: string;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 interface HighlightConfig {
@@ -136,6 +137,7 @@ interface HighlightConfig {
   includeWhitespace: boolean;
   highlightAll: boolean; // true = all occurrences, false = first only per line
   isGlobal?: boolean; // true = applies to all files, false = file-specific
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 interface FolderFile {
@@ -204,6 +206,7 @@ interface SearchConfigDef {
   enabled: boolean;
   isGlobal: boolean;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 // A reusable, named pattern-property: a regex whose 1st capture group (or whole
@@ -216,6 +219,7 @@ interface PatternPropertyDef {
   patternFlags?: string;
   unit?: string;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 // A reusable, named search/regex pattern in the Pattern Library. Written once,
@@ -270,6 +274,7 @@ interface SearchConfigSessionDef {
   configs: SearchConfigDef[];
   isGlobal: boolean;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 interface BaselineRecord {
@@ -816,8 +821,8 @@ interface Api {
   compilePattern: (input: { mode: 'plain' | 'grok' | 'paint' | 'regex'; text?: string; sample?: string; spans?: Array<{ start: number; end: number; name: string }>; flags?: string; matchCase?: boolean; wholeWord?: boolean; invert?: boolean }) => Promise<{ ok: boolean; source: string; flags: string; error?: string; warnings: string[]; mode: string }>;
 
   // Named constants (captured from a selection via "Save as constant…")
-  saveConstant: (name: string, value: string) => Promise<{ success: boolean; error?: string }>;
-  getConstants: () => Promise<{ success: boolean; entries?: Array<{ name: string; value: string; createdAt: string; updatedAt: string }> }>;
+  saveConstant: (name: string, value: string, description?: string) => Promise<{ success: boolean; error?: string }>;
+  getConstants: () => Promise<{ success: boolean; entries?: Array<{ name: string; value: string; createdAt: string; updatedAt: string; description?: string }> }>;
   deleteConstant: (name: string) => Promise<{ success: boolean; removed?: boolean }>;
 
   // Active scope ("Use filter/search/selection as scope" + breadcrumb)
diff --git a/src/shared/types.ts b/src/shared/types.ts
index fbb22a1..f382b99 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -44,6 +44,7 @@ export interface Bookmark {
   label: string;
   color: string;
   lineText?: string;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 export interface Annotation {
@@ -74,6 +75,7 @@ export interface Highlight {
   includeWhitespace: boolean;
   highlightAll: boolean; // true = all occurrences, false = first only per line
   isGlobal?: boolean; // true = applies to all files, false = file-specific
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 export interface HighlightGroup {
@@ -160,6 +162,7 @@ export interface SearchConfig {
   enabled: boolean;
   isGlobal: boolean;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 // A reusable, named pattern-property: a regex whose 1st capture group (or the
@@ -171,6 +174,7 @@ export interface PatternProperty {
   patternFlags?: string;
   unit?: string;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 // A reusable, named search/regex pattern in the Pattern Library. Written once,
@@ -308,6 +312,7 @@ export interface SearchConfigSession {
   configs: SearchConfig[];
   isGlobal: boolean;
   createdAt: number;
+  description?: string; // optional human/AI note: what this is for / why it was added
 }
 
 // Live connection info returned to renderer
diff --git a/src/tests/constantsStore.test.ts b/src/tests/constantsStore.test.ts
index 9db82ac..2541544 100644
--- a/src/tests/constantsStore.test.ts
+++ b/src/tests/constantsStore.test.ts
@@ -67,6 +67,32 @@ describe('ConstantsStore', () => {
     });
   });
 
+  describe('description (optional human/AI note)', () => {
+    it('stores a description when provided', () => {
+      store.save('sessionId', 'abc-123', undefined, 'the auth session token seen at the crash');
+      expect(store.getAll()[0].description).toBe('the auth session token seen at the crash');
+    });
+
+    it('leaves description undefined when not provided', () => {
+      store.save('deviceId', 'dev-9');
+      expect(store.getAll()[0].description).toBeUndefined();
+    });
+
+    it('can set/replace the description on upsert without dropping it', () => {
+      store.save('k', 'v1');
+      store.save('k', 'v2', undefined, 'why this matters');
+      expect(store.getAll()[0].value).toBe('v2');
+      expect(store.getAll()[0].description).toBe('why this matters');
+    });
+
+    it('round-trips the description through disk', () => {
+      store.save('k', 'v', undefined, 'purpose note');
+      store.flush();
+      const reloaded = new ConstantsStoreImpl(filePath);
+      expect(reloaded.getAll()[0].description).toBe('purpose note');
+    });
+  });
+
   describe('getAll()', () => {
     it('returns constants sorted by name ascending', () => {
       store.save('zeta', '1');