GLS US (Golden State Overnight / GSO) Tracking API & MCP

Query live GLS US (glsus, formerly Golden State Overnight / GSO) West Coast package status and scan history in a single synchronous GET request or MCP tool call.

Important — Always pass ?carrier=glsus (or "carrier": "glsus" in MCP): GLS US is never auto-detected (matches: () => false, no mayMatch). Because GLS US uses 8–11 digit uncheck-digited GSO numbers (typically 9 digits like 512345678 or 758110995) as well as arbitrary shipper reference numbers (CA0W2208048, 20-digit references) that collide with other carriers—and because GLS US's system answers generic placeholder numbers shippers reuse—you must always specify ?carrier=glsus.

Overview & Quick FactsCopy Anchor Link

Why developers use lastscanned for GLS US / GSOCopy Anchor Link

• Deduplicates reused tracking numbers automatically: Shippers on GLS US frequently reuse tracking numbers or reference numbers across multiple shipments over time, causing raw GLS US API responses to return multiple shipment objects for a single number. lastscanned automatically sorts matching shipments by newest shipDate and latest scan timestamp so you always get the active parcel.
• Translates GSO service codes & return-to-sender (RTS) states: Raw GLS US responses return legacy GSO service codes (CPS → "GLS Ground", PDS → "Priority Overnight", EPS → "Early Priority Overnight", NPS → "Noon Priority Overnight", SDS → "Saturday Delivery", ESS → "Early Saturday Delivery") and stuff return reasons ("RTS - UNABLE TO CONTACT RCPNT") into the signedBy field on returned shipments. lastscanned maps service names cleanly and clears signedBy to null unless the parcel is actually delivered.
• West Coast timezone normalization: GLS US prints scan times in local wall-clock time without a UTC offset. lastscanned maps Pacific states (CA, NV, OR, WA → America/Los_Angeles) and Arizona (AZ → America/Phoenix, no DST) to compute accurate UTC timestamp values alongside localTime.

Tracking Number Formats & Why ?carrier=glsus Is RequiredCopy Anchor Link

Why GLS US is never auto-detectedCopy Anchor Link

1. No check digit or fixed prefix on 9-digit GSO numbers: Standard 9-digit numbers (512345678) have no check digit, and 20-digit shipper references collide directly with FedEx and DHL Paket.
2. Shipper-supplied tracking numbers: GLS US indexes parcels by whatever barcode or reference number the shipper prints on the label, and even answers test/placeholder numbers (123456789) that shippers have reused. Requiring ?carrier=glsus guarantees zero false positives on other carriers' numbers.

Synchronous GET Request & Normalized JSON ResponseCopy Anchor Link

curlCopy Anchor Link

curl -s "https://api.lastscanned.com/v1/track/512345678?carrier=glsus" \
  -H "Authorization: Bearer $LASTSCANNED_API_KEY"

JavaScript / TypeScript (fetch)Copy Anchor Link

const res = await fetch("https://api.lastscanned.com/v1/track/512345678?carrier=glsus", {
  headers: { Authorization: `Bearer ${process.env.LASTSCANNED_API_KEY}` },
});
const pkg = await res.json();
console.log(pkg.status, pkg.service, pkg.signedBy);

MCP track_package tool callCopy Anchor Link

{
  "tool": "track_package",
  "arguments": {
    "tracking_number": "512345678",
    "carrier": "glsus"
  }
}

Normalized TrackingResult JSON responseCopy Anchor Link

{
  "carrier": "glsus",
  "trackingNumber": "512345678",
  "status": "delivered",
  "statusDescription": "SHIPMENT DELIVERED",
  "service": "GLS Ground",
  "deliveredAt": "2026-10-24T20:15:00Z",
  "deliveredAtLocal": "2026-10-24T13:15:00",
  "signedBy": "FRONT DOOR",
  "destination": {
    "city": "OAKLAND",
    "state": "CA",
    "country": "US"
  },
  "estimatedDelivery": null,
  "events": [
    {
      "timestamp": "2026-10-24T20:15:00Z",
      "localTime": "2026-10-24T13:15:00",
      "status": "delivered",
      "description": "SHIPMENT DELIVERED",
      "location": "OAKLAND, CA",
      "code": null
    },
    {
      "timestamp": "2026-10-24T15:10:00Z",
      "localTime": "2026-10-24T08:10:00",
      "status": "out_for_delivery",
      "description": "ON ROUTE FOR DELIVERY",
      "location": "HAYWARD, CA",
      "code": null
    },
    {
      "timestamp": "2026-10-24T11:42:00Z",
      "localTime": "2026-10-24T04:42:00",
      "status": "in_transit",
      "description": "SCANNED AT DELIVERY DEPOT",
      "location": "HAYWARD, CA",
      "code": null
    },
    {
      "timestamp": "2026-10-23T22:05:00Z",
      "localTime": "2026-10-23T15:05:00",
      "status": "label_created",
      "description": "LABEL CREATED",
      "location": null,
      "code": null
    }
  ]
}

Related ResourcesCopy Anchor Link

• Live browser lookup tool: Track a GLS US package live on lastscanned.com/lookup/glsus
• Carrier hub: All 31 supported carriers
• Regex & check digits: Tracking number formats & auto-detection
• AI support workflows: WISMO AI agents & synchronous tracking