diff --git a/src/lib/api/adapters/grid.adapter.ts b/src/lib/api/adapters/grid.adapter.ts
index af3f8370..0e8ed984 100644
--- a/src/lib/api/adapters/grid.adapter.ts
+++ b/src/lib/api/adapters/grid.adapter.ts
@@ -11,6 +11,7 @@ import { BaseAdapter } from './base.adapter'
 import type { AdapterOptions } from './types'
 import type { GridWeapon, GridCharacter, GridSummon } from '$lib/types/api/party'
 import { DEFAULT_ADAPTER_CONFIG } from './config'
+import { validateGridWeapon, validateGridCharacter, validateGridSummon } from '$lib/utils/gridValidation'
 
 // GridWeapon, GridCharacter, and GridSummon types are imported from types/api/party
 // Re-export for test files and consumers
@@ -103,7 +104,14 @@ export class GridAdapter extends BaseAdapter {
             body: { weapon: params },
             headers
         })
-        return response.gridWeapon
+
+        // Validate and normalize response
+        const validated = validateGridWeapon(response.gridWeapon)
+        if (!validated) {
+            throw new Error('API returned incomplete GridWeapon data')
+        }
+
+        return validated
     }
 
 	/**
@@ -207,7 +215,14 @@ export class GridAdapter extends BaseAdapter {
             body: { character: params },
             headers
         })
-        return response.gridCharacter
+
+        // Validate and normalize response
+        const validated = validateGridCharacter(response.gridCharacter)
+        if (!validated) {
+            throw new Error('API returned incomplete GridCharacter data')
+        }
+
+        return validated
     }
 
 	/**
@@ -311,7 +326,14 @@ export class GridAdapter extends BaseAdapter {
             body: { summon: params },
             headers
         })
-        return response.gridSummon
+
+        // Validate and normalize response
+        const validated = validateGridSummon(response.gridSummon)
+        if (!validated) {
+            throw new Error('API returned incomplete GridSummon data')
+        }
+
+        return validated
     }
 
 	/**
diff --git a/src/lib/utils/gridValidation.ts b/src/lib/utils/gridValidation.ts
new file mode 100644
index 00000000..c444c692
--- /dev/null
+++ b/src/lib/utils/gridValidation.ts
@@ -0,0 +1,100 @@
+/**
+ * Grid Validation Utilities
+ *
+ * Validates and normalizes grid item data from API responses.
+ * Handles legacy 'object' property and ensures complete nested entity data.
+ *
+ * @module utils/gridValidation
+ */
+
+import type { GridWeapon, GridCharacter, GridSummon } from '$lib/types/api/party'
+
+/**
+ * Validates that a GridWeapon has complete nested weapon data.
+ * Normalizes legacy 'object' property to 'weapon' if needed.
+ *
+ * @param raw - Raw grid weapon data from API
+ * @returns Validated GridWeapon or null if incomplete
+ *
+ * @example
+ * ```typescript
+ * // Valid data
+ * const validated = validateGridWeapon({
+ *   id: '123',
+ *   position: 0,
+ *   weapon: { granblueId: '1040', name: {...} }
+ * })
+ *
+ * // Legacy data with 'object' property
+ * const validated = validateGridWeapon({
+ *   id: '123',
+ *   position: 0,
+ *   object: { granblueId: '1040', name: {...} }
+ * }) // Automatically normalized to 'weapon'
+ * ```
+ */
+export function validateGridWeapon(raw: any): GridWeapon | null {
+	if (!raw || typeof raw !== 'object') return null
+
+	// Handle legacy API responses that use 'object' instead of 'weapon'
+	const weapon = raw.weapon || raw.object
+
+	if (!weapon || !weapon.granblueId) {
+		console.warn('GridWeapon missing nested weapon data:', raw)
+		return null
+	}
+
+	return {
+		...raw,
+		weapon, // Ensure 'weapon' property exists
+		object: undefined // Remove legacy 'object' property
+	} as GridWeapon
+}
+
+/**
+ * Validates that a GridCharacter has complete nested character data.
+ * Normalizes legacy 'object' property to 'character' if needed.
+ *
+ * @param raw - Raw grid character data from API
+ * @returns Validated GridCharacter or null if incomplete
+ */
+export function validateGridCharacter(raw: any): GridCharacter | null {
+	if (!raw || typeof raw !== 'object') return null
+
+	const character = raw.character || raw.object
+
+	if (!character || !character.granblueId) {
+		console.warn('GridCharacter missing nested character data:', raw)
+		return null
+	}
+
+	return {
+		...raw,
+		character,
+		object: undefined
+	} as GridCharacter
+}
+
+/**
+ * Validates that a GridSummon has complete nested summon data.
+ * Normalizes legacy 'object' property to 'summon' if needed.
+ *
+ * @param raw - Raw grid summon data from API
+ * @returns Validated GridSummon or null if incomplete
+ */
+export function validateGridSummon(raw: any): GridSummon | null {
+	if (!raw || typeof raw !== 'object') return null
+
+	const summon = raw.summon || raw.object
+
+	if (!summon || !summon.granblueId) {
+		console.warn('GridSummon missing nested summon data:', raw)
+		return null
+	}
+
+	return {
+		...raw,
+		summon,
+		object: undefined
+	} as GridSummon
+}