Adapted from Using Archives: A Guide to Effective Research by Laura Schmidt
Catalogs and Databases: Search WorldCat or check whether the archives that you are evaluating has a link on its website to catalogs or databases that allow you to search their holdings. Search holdings by keyword, subject, or title. Many of these catalogs will link you to finding aids (see below) which will provide more detail about what a specific collection holds.
Most libraries cataloged printed materials, like their cataloged manuscripts and archival collections can be found by searching the library's general catalog.
You may apply various limits (location, date, language, type of material) when searching. And you may also search by rare book collection, which is often reflected in the catalog record. For example:
Finding Aids: A finding aid (sometimes called inventory, collection listing, register, or calendar) is a document that describes of the contents of a collection.
1) If the archives you are evaluating provides direct access to finding aids on its website, browse or search the finding aids for content relating to your research.
Some institutions have finding aids databases:
2) Search for finding aids in google (use "finding aids") and the finding aid portals:
3) Check ArchiveGrid at http://www.archivegrid.org/web/index.jsp. This database contains nearly a million collection descriptions from thousands of libraries, archives, and museums (requires purchase or subscription).
Finding aids come in all kinds of formats. Some archives just have paper copies to use on-site, while others have word processing documents, PDF, or HTML/XML finding aids that can be viewed on their websites.