Look up a service type code, decode a package barcode or ask a question about mailing. Each answer links the USPS words it rests on.
342 service type codes2,933 terms84 product pagesUnofficial, not affiliated with USPS
Type a code or a term, paste a tracking number, or ask in your own words. The box and the agent draw their answers with the same blocks, from the same USPS documents.
055
Priority Mail: USPS Tracking
In a tracking number. The Mailer ID and serial number are examples.
Service type code list effective June 24, 2026, row 23.
9205 5912 3456 7812 3456 74
The Mailer ID and serial number are examples.
Which service type codes did the June 24, 2026 list add?
The June 24, 2026 list added four service type codes. Each is marked "New" with a change date of "Jul 26". All four are in mail class S2 (USPS Marketing Mail), carry the banner text "USPS TRACKING #", and are flagged Y for both CS and eVS.
Recorded November 1, 2026: 7.9 s, 4 sources.
Ask it nowThe barcode starts with 420 and the destination ZIP Code, and the label doesn’t print either one. The tracking number under the bars is everything after the ZIP Code.
Priority Mail: USPS Tracking. Banner text USPS TRACKING #.
The Mailer ID and serial number are examples. Every other field is a real value.
84 pages on USPS products and services, each saying what the product is and citing the USPS documents it quotes.
The code tables, specs and documents postalref holds, and the barcode terms it explains. The guides index every other name it knows.
USPS posts the list as a spreadsheet on PostalPro, and postalref compares each of its 8 editions with the one before.
| Code | Description | Class |
|---|---|---|
| 249 | USPS Marketing Mail: Heavy Printed Matter Commercial Marketing Parcels USPS Tracking | S2 |
| 250 | USPS Marketing Mail: Heavy Printed Matter Commercial Marketing Parcels | S2 |
| 254 | USPS Marketing Mail: Heavy Printed Matter Nonprofit Commercial Marketing Parcels USPS Tracking | S2 |
| 258 | USPS Marketing Mail: Heavy Printed Matter Nonprofit Commercial Marketing Parcels | S2 |
Removed: 12 codes, 389, 390, 391, 392, 393, 604, 778, 779, 780, 781, 782, 783.
Every definition and product page quotes USPS and names the page it quotes. A quote that isn’t on that page fails the build.
Any client that takes a remote MCP server can add postalref by its URL. Its tools only read, and it needs no key or sign-in.
claude mcp add --transport http --scope user postalref https://postalref.com/mcpcodex mcp add postalref --url https://postalref.com/mcp# Any other client
https://postalref.com/mcp# 8 tools
No. It is an unofficial reference, not affiliated with or endorsed by the United States Postal Service. Every page links the USPS documents it cites, and those documents are the authority.
You can search the 342 service type codes in the USPS list effective June 24, 2026, by number or by name. You can also search 2,933 USPS mailing terms, most of them defined in Publication 32, USPS’s glossary of postal terms.
The service type codes come from the list effective June 24, 2026, and the barcode rules from Publication 199, Version 35, July 2, 2026. An answer in the box at the top names the revision and effective date of its source. A product page cites the document, page and words it uses, and links the exact file.
From USPS documents on postalpro.usps.com. postalref models 13 of them, including the IMpb specification, Publication 199 and the Service Type Code List, Appendix I. The terms’ definitions quote 405 documents, and each product page cites the PostalPro pages and files it draws on. Each fact names its document and page, and a citation that doesn’t resolve fails the build.
A person fetches each new revision and rebuilds the site. Nothing runs on a schedule yet. For the service type code list, the changes page then lists every code each edition added, removed or changed. When USPS changes a passage that postalref’s own explanation cites, the explanation keeps citing the older revision until a person reviews it.
Yes. Copy the prompt into a chat, or add https://postalref.com/mcp to your agent as an MCP server. Its tools only read. An agent without MCP can start at https://postalref.com/llms.txt, which lists every page, and read each page as Markdown at its address with .md added, or every page in one file at https://postalref.com/llms-full.txt.
No. The first version has no accounts, keys or paid plans, so pages, files and the MCP server are open to anyone.
No. The check digit only catches mistyped digits. Anyone can compute it with the method in the IMpb specification, so it says nothing about whether postage was paid.
Package barcodes of 22, 26, 30 or 34 digits whose tracking number starts with 92, 93, 94 or 95. Letters and flats carry a different barcode, which this decoder doesn’t read.
The barcode starts with 420 and the destination ZIP Code, and the label doesn’t print either one. The tracking number under the bars is everything after the ZIP Code.