Track Yanwen (…YP / YW…) parcels and extract the final-mile USPS tracking number in one API call.

Yanwen Logistics (S10 …YP and YW… waybills) consolidates cross-border e-commerce shipments from China and hands US-bound parcels to USPS (or domestic consolidators) after port arrival. Querying GET /v1/track/:number on lastscanned returns Yanwen's international scan history and surfaces the final-mile USPS barcode in the top-level message field ('Handed to USPS as 420...').

Barcode transition: Yanwen to USPS

When Yanwen clears customs and hands off to USPS, lastscanned surfaces the secondary tracking number in the top-level message field.

Yanwen lookup →Format & check-digit detector →
Origin / middle-mile carrier
Yanwen (yanwen)
Yanwen S10 / Commercial Waybill
2 letters + 9 digits + YP (S10 check digit) or YW + 3 letters + 12 digits
Origin example
UV123456785YP
Final-mile carrier
USPS (usps)
USPS Domestic IMpb
92… / 94… (22 digits) or 420+ZIP+92… (30 digits)
Final-mile example
420100019261290100130612345678
Extracted in .message
Handed to USPS as 420100019261290100130612345678

How the Yanwen → USPS handoff works

Follow the parcel across both networks without waiting on asynchronous webhooks or losing visibility at the handoff boundary.

1. Pass 1 S10 check-digit validation on …YP waybills
lastscanned validates the UPU S10 Mod-11 check digit on 13-character …YP numbers (and matches 17-character YW… numbers) to route immediately to yanwen.
2. Extract the exchange USPS barcode from message
When Yanwen generates the US domestic label (exchangeNumber), lastscanned normalizes it into message: 'Handed to USPS as 420...'.
3. Follow the USPS barcode to delivery
Query GET /v1/track/420... to retrieve USPS regional distribution and local carrier delivery scans.
Yanwen regex & check digit
/^[A-Z]{2}\d{9}YP$/ with s10(n) validation, or /^YW[A-Z]{3}\d{12}$/.
Handoff field
Top-level message string: 'Handed to USPS as <number>'.
Batch support
Track up to 100 Yanwen and USPS numbers simultaneously via GET /v1/track?numbers=...

Chain Yanwen → USPS in code or MCP

Resolve both legs synchronously in TypeScript, curl, or your AI support agent via Streamable HTTP MCP.

Get an API keyWISMO agent guide

REST (Synchronous GET)

# 1. Query Yanwen origin waybill (extracts final-mile barcode in .message):
curl "https://api.lastscanned.com/v1/track/UV123456785YP" \
  -H "Authorization: Bearer lsk_live_YOUR_API_KEY"

# 2. Query the extracted USPS barcode:
curl "https://api.lastscanned.com/v1/track/420100019261290100130612345678" \
  -H "Authorization: Bearer lsk_live_YOUR_API_KEY"

TypeScript (Automatic Handoff Chaining)

const headers = { Authorization: `Bearer ${process.env.LASTSCANNED_API_KEY}` };
const originRes = await fetch(`https://api.lastscanned.com/v1/track/${encodeURIComponent(number)}`, { headers });
const originPkg = await originRes.json();

// Extract secondary barcode from top-level message ("Handed to USPS as 420100019261290100130612345678")
const handoff = originPkg.message?.match(/^Handed to (.+?) as ([A-Z0-9-]+)$/i);
if (handoff) {
  const [, , lastMileNumber] = handoff;
  const destRes = await fetch(`https://api.lastscanned.com/v1/track/${encodeURIComponent(lastMileNumber)}`, { headers });
  const destPkg = await destRes.json();
}

Remote MCP (Claude Code / Cursor / ChatGPT)

claude mcp add --transport http lastscanned https://mcp.lastscanned.com \
  --header "Authorization: Bearer lsk_live_YOUR_API_KEY"

Yanwen to USPS Last-Mile Handoff Tracking FAQ

How do I find the USPS tracking number for a Yanwen (…YP) package?
Paste your Yanwen tracking number (ending in YP or starting with YW) into the lookup above, or call GET /v1/track/:number. The top-level message field returns the USPS exchange tracking number.
Why does my Yanwen tracking number have a 30-digit USPS exchange number starting with 420?
USPS Intelligent Mail package barcodes (IMpb) often prepend '420' plus the 5-digit destination ZIP code ahead of the 22-digit 92… tracking number. lastscanned's USPS detector natively accepts both the 30-digit 420+ZIP+92… format and the 22-digit 92… format.
Can AI agents resolve Yanwen-to-USPS handoffs automatically?
Yes. When connected to https://mcp.lastscanned.com, an AI agent sees the 'Handed to USPS as ...' message in the first tool result and can immediately invoke track_package on the USPS barcode.

Other carrier handoff guides

Explore cross-border last-mile barcode extraction and domestic USPS consolidator overrides across all 31 carriers.

"USPS Currently Awaiting Package" 92… Checker →Tracking Number Format & Check-Digit Detector →

All 31 supported carriers

Major carriers

Regional and last mile

Cross-border