> ## Documentation Index > Fetch the complete documentation index at: https://docs.arcuserp.com/llms.txt > Use this file to discover all available pages before exploring further. # List inventory balances > Per-product per-location on_hand balances. Drives from active+tracked products with LEFT JOIN to inventory_balances (all SKUs visible even at 0). The `available` field is GENERATED (on_hand - allocated) and is readOnly. ## OpenAPI ````yaml /openapi.yaml get /inventory/balances openapi: 3.1.0 info: title: Arcus ERP Public API version: 1.0.0 description: > Arcus ERP public REST API. Designed for external integrations and data migration. **Authentication.** Bearer token (API key) via the `Authorization` header. Format: `Authorization: Bearer ark_live_ent__` (or `ark_test_*` for sandbox). API keys are issued per-entity in **Settings > Developers > API Keys**. **Entity scoping.** The entity is encoded in the API key prefix; routes are flat (e.g. `/v1/accounts`, `/v1/orders`, `/v1/products`). A small set of platform endpoints (migration, reconciliation, events, webhook endpoints, API keys) use the `/v1/entities/{entity_id}/...` form -- those are noted in their tags. **Key capabilities.** - Related-resource hydration via `?expand[]=` (see `x-arcus-expand` on each resource). - Cursor-based pagination (`starting_after` / `ending_before` / `limit`). - Idempotency via the `Idempotency-Key` header. - Webhook events for asynchronous notification. - Conditional requests / ETag for cache validation. servers: - url: https://api.arcuserp.com/v1 description: Arcus ERP API (accepts both live `ark_live_*` and test `ark_test_*` keys) - url: https://dev-api.arcuserp.com/v1 description: >- Dev sandbox API (test-only data, accepts `ark_test_*` keys against dev RDS) security: [] paths: /inventory/balances: get: tags: - Inventory summary: List inventory balances description: > Per-product per-location on_hand balances. Drives from active+tracked products with LEFT JOIN to inventory_balances (all SKUs visible even at 0). The `available` field is GENERATED (on_hand - allocated) and is readOnly. operationId: listInventoryBalances parameters: - name: product_id in: query schema: type: string format: uuid - name: location_id in: query description: Layer 4 location filter schema: type: string format: uuid - name: variant_id in: query schema: type: string format: uuid - name: low_stock_only in: query schema: type: boolean - name: page in: query schema: type: integer minimum: 1 default: 1 - name: per_page in: query schema: type: integer minimum: 1 maximum: 100 default: 25 - name: expand[] in: query schema: type: array items: type: string enum: - data.product - data.location - data.lot style: form explode: true responses: '200': description: List of inventory balances content: application/json: schema: type: object properties: object: type: string enum: - list data: type: array items: $ref: '#/components/schemas/InventoryBalance' total: type: integer page: type: integer per_page: type: integer total_pages: type: integer example: object: list data: - id: inv-bal-uuid-0001 entity_id: ent-uuid-here product_id: prod-uuid-0001 location_id: loc-uuid-0001 variant_id: null on_hand: 150 allocated: 20 available: 130 on_purchase_order: 50 total_value: 2775 avg_unit_value: 18.5 product_title: Widget Pro XL location_name: Main Warehouse created_at: '2025-06-01T12:00:00Z' updated_at: '2026-05-01T08:00:00Z' total: 1 page: 1 per_page: 25 total_pages: 1 '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' security: - ApiKeyAuth: [] components: schemas: InventoryBalance: type: object description: Per-product per-location inventory balance. available is readOnly. properties: id: type: string format: uuid entity_id: type: string format: uuid product_id: type: string format: uuid location_id: type: string format: uuid variant_id: type: string format: uuid nullable: true on_hand: type: integer description: 'SSOT writer: utils/inventory-helpers.mjs::recordMovement' allocated: type: integer description: 'SSOT writer: recordMovement via reserveInventory' available: type: integer readOnly: true description: 'GENERATED (on_hand - allocated). readOnly: DO NOT WRITE.' on_purchase_order: type: integer total_value: type: number avg_unit_value: type: number product_title: type: string location_name: type: string created_at: type: string format: date-time updated_at: type: string format: date-time ErrorEnvelope: type: object description: | Canonical error response envelope. All API errors use this shape. required: - error - code properties: error: type: string description: Machine-readable error key example: not_found code: type: string description: Machine-readable error code (often same as error) example: not_found type: type: string enum: - validation_error - permission_error - not_found - conflict - rate_limit - internal - expand_error - not_implemented example: not_found hint: type: string description: Human-readable one-sentence explanation (English) example: >- The requested order does not exist or does not belong to this entity. param: type: string description: The parameter that caused the error, if applicable example: expand[0] required: type: string description: The scope required (only on insufficient_scope errors) example: accounts:read request_id: type: string description: >- Unique request ID for support tracing (maps to CloudWatch log stream) example: req_abc123 responses: Error: description: Error response (400/401/403/404/409/422/429/500) content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' securitySchemes: ApiKeyAuth: type: http scheme: bearer description: | API key issued per entity via Settings > Developers > API Keys. Each key carries scopes (e.g. orders:read, products:write). Bearer token format: Authorization: Bearer ark_live_ent__ Test keys use ark_test_ent__. Both are issued per entity via Settings > Developers > API Keys. ````