Your book exists in your catalog. It also exists in WorldCat, in the Library of Congress, on AbeBooks, in the ISTC, on Google Books, and possibly in the sale records of Christie's. External links connect your record to all of these.
What External Links Are
An external link is a URL that connects your book record to an outside resource — a library catalog, a digital library, a marketplace, a provenance database, or anything else relevant.
Shelvd ships with 64 system-defined link types across eight categories:
Bibliographic (7): WorldCat, VIAF, Wikidata, Wikipedia, ISNI, Open Library, KVK
Short Title Catalogs (9): ISTC, GW, USTC, ESTC, STCN, STCV, VD16, VD17, EDIT16
National & Regional Catalogs (21): KBR, KB NL, BnF, SUDOC, CCFr, British Library, DNB, BSB, SBN/ICCU, BNE, Library of Congress, K10plus, Unicat, Swisscovery, BIBSYS, ÖNB, Libris, Finna, NDL, Trove, DanBib
Digital Libraries (8): Gallica, Europeana, Google Books, HathiTrust, Internet Archive, MDZ, CERL HPB, Biodiversity Heritage Library
Provenance & Specialist (4): CERL Thesaurus, MEI, data.bnf.fr, GND
Antiquarian & Marketplaces (6): AbeBooks, ZVAB, Biblio, viaLibri, Bookfinder, Catawiki
Auction Houses & Prices (5): Rare Book Hub, Christie's, Sotheby's, Bonhams, Drouot
Community (2): Goodreads, LibraryThing
Plus a Publisher Website type and a catch-all Other type.
How They Work
On the book's Add or Edit page, scroll to the External Links section. Select a link type from the dropdown, paste the URL, and save. The link appears on the book detail page with a favicon and clickable URL.
Auto-Fill from Lookup
When you add a book via Library Lookup, Shelvd automatically creates an external link back to the source record. Search a book in the Library of Congress? The LOC catalog URL is saved. Find it on Open Library? That link is saved too.
This means that over time, books acquired through lookup accumulate a web of external references without you doing anything extra.
Custom Link Types
If none of the 64 system types fit, you can create custom link types in Settings → External Links. Give it a name, optionally a domain, and a category. Your custom types appear alongside the system types on book forms.
Configuring Your Link Types
Not all 64 types are relevant to every collection. In Settings → External Links, you can activate or deactivate types. Deactivated types don't appear in dropdowns but existing links are preserved.
A collector of French literature might activate BnF, Gallica, SUDOC, and data.bnf.fr while deactivating NDL and Trove. A collector of incunabula would want ISTC, GW, CERL HPB, and MEI. Configure once, benefit always.