An article's quality assessment is generated from the class parameter in the {{WikiProject banner shell}}. Articles that have the {{WikiProject Thomas}} project banner on their talk page will be added to the appropriate categories by quality.

The following values may be used for the class parameter to describe the quality of the article (see Wikipedia:Content assessment for assessment criteria):

FA (for featured articles only; adds articles to Category:FA-Class articles)		FA
A (adds articles to Category:A-Class articles)		A
GA (for good articles only; adds articles to Category:GA-Class articles)		GA
B (adds articles to Category:B-Class articles)		B
C (adds articles to Category:C-Class articles)		C
Start (adds articles to Category:Start-Class articles)		Start
Stub (adds articles to Category:Stub-Class articles)		Stub
FL (for featured lists only; adds articles to Category:FL-Class articles)		FL
List (adds articles to Category:List-Class articles)		List
SIA (for set index articles; adds articles to Category:SIA-Class articles)		SIA
Future (for articles about future events; adds articles to Category:Future-Class articles)		Future

For non-standard grades and non-mainspace content, the following values may be used for the class parameter:

Category (for categories; adds pages to Category:Category-Class pages)		Category
Disambig (for disambiguation pages; adds pages to Category:Disambig-Class pages)		Disambig
Draft (for drafts; adds pages to Category:Draft-Class pages)		Draft
FM (for featured media only; adds pages to Category:FM-Class pages)		FM
File (for files and timed text; adds pages to Category:File-Class pages)		File
Portal (for portal pages; adds pages to Category:Portal-Class pages)		Portal
Project (for project pages; adds pages to Category:Project-Class pages)		Project
Redirect (for redirect pages; adds pages to Category:Redirect-Class pages)		Redirect
Template (for templates and modules; adds pages to Category:Template-Class pages)		Template
NA (for any other pages where assessment is unnecessary; adds pages to Category:NA-Class pages)		NA
??? (articles for which a valid class has not yet been provided are listed in Category:Unassessed articles)		???

An article's importance assessment is generated from the importance parameter in the {{WikiProject Thomas}} project banner on its talk page:

The following values may be used for the importance parameter to describe the relative importance of the article within the project (see Wikipedia:Version 1.0 Editorial Team/Priority of topic for assessment criteria):

Note: Bottom-importance is not used in this WikiProject. When you try to assess an article as bottom-importance, it instead sorts the article into Category:Unknown-importance Thomas articles.

The criteria used for rating article importance are not meant to be an absolute or canonical view of how significant the topic is. Rather, they attempt to gauge the probability of the average reader of Wikipedia needing to look up the topic (and thus the immediate need to have a suitably well-written article on it). Thus, subjects with greater popular notability may be rated higher than topics which are arguably more "important" but which are of interest primarily to fans of Thomas.

Note that general notability need not be from the perspective of editor demographics; generally notable topics should be rated similarly regardless of the country or region in which they hold said notability. Thus, topics which may seem obscure to a Western audience—but which are of high notability in other places—should still be highly rated.

Note: The table is only updated every few days, and may be out of date.