Tag (#tag)

A tag is a keyword attached to a note, usually written inline as #word, that groups notes across folders and can be filtered on.

A tag is a label on a note. Unlike a folder, a note can carry many tags, and a tag can span every folder. In Markdown notes the usual form is an inline hashtag, #meeting, written anywhere in the text; some tools also or instead take a list in front matter.

Origin

Tagging as user-assigned keywords spread through the 2000s web (del.icio.us bookmarks, Flickr photos) as an alternative to fixed categories. The # prefix comes from IRC channel names by way of Twitter: Chris Messina proposed #barcamp-style groups in an August 2007 tweet, and Twitter started hyperlinking hashtags to search in 2009 (Wikipedia: Hashtag). Note tools adopted the inline form because it needs no UI: the tag is part of the text, survives copy and paste, and is visible in any editor.

How it works

The tool scans each note for # followed by a word, builds an index from tag to notes, and offers a filter or search operator. Nested tags extend the word with slashes, #work/project, so that filtering on #work also matches its children; Obsidian documents this exact behaviour and rule set: letters, numbers, _, - and /, at least one non-digit, case-insensitive (Obsidian: Tags). Completion after typing # keeps spelling consistent, which matters because #meeting and #meetings are two tags.

Pitfalls

# is overloaded in Markdown. # Heading at the start of a line is a heading, #1984 may be an issue number, and a # inside a code span is code. Parsers differ on which of these they treat as tags. Tags do not carry meaning beyond their name, so a taxonomy drifts: #todo, #task and #tasks accumulate unless there is completion or a tag list to check against. Front-matter tags and inline tags are two systems, and a tool that reads only one will miss the other. Shell users hit one more: # starts a comment, so --tag '#work' needs quotes.

In other tools

Obsidian reads inline #tags and a tags list in properties, with a tags view for browsing. jrnl uses @ as its tag symbol precisely because # is reserved in shells, and warns when a new tag looks like a typo of an existing one (jrnl docs). nb accepts --tags tag1,tag2 on nb add and #tagging in the text (nb README).

In tnotes

tnotes parses #tags from the note text, including nested ones like #work/project. There is no tag field; the text is the source of truth. In the editor, typing # then tab completes from existing tags, and ctrl+click on a tag filters the list to it. Tags are highlighted in the theme.tag colour (green by default) when editor.highlight = "color".

The CLI filters and creates by tag; a leading # is stripped so quoting is harmless:

tnotes ls --tag work
tnotes search "invoice" --tag '#work/acme' --json
tnotes new "Standup" --tag work

ls --json includes a tags array per note. A tags: line in a header is not parsed; write the tag inline instead. See /docs/cli and /glossary/frontmatter.