---
title: "Tags"
description: "Hierarchical tags as an axis of navigation: a facet filter in the Feed and the Graph."
---

# Tags

Tags in Notarium are a full-fledged axis of navigation, not just labels on cards. You set them in a note's frontmatter, and Notarium turns them into a **facet filter**: one click narrows the Feed or the Graph down to the topic you want. Tags are **hierarchical** (via `/`) and **case-insensitive**.

## How to set tags

Tags live in a note's frontmatter — the ordinary YAML block at the top of the file:

```md
---
title: Notes on transformers
tags: [ml/nlp, reading]
---

Note body…
```

Hierarchy is expressed with `/`: `ml/nlp` is the tag `nlp` inside `ml`. Case doesn't matter — `ML` and `ml` count as one tag.

## Hierarchy and filtering

The key property of the hierarchy is that **a parent includes its children**. Filtering by `ml` shows notes tagged `ml`, `ml/nlp`, and `ml/cv` alike. That lets you keep tags as fine-grained as you find convenient without losing the ability to view a topic as a whole.

The filter works as a **union (OR)**: select several tags and the selection widens — notes matching any of them show up. Select nothing and there's no filter.

The filter widget speaks the same language in two places:

- **In the [Feed](/docs/guides/feed/)** — a tag panel next to folders and text search. Tags are part of the URL, so a filtered view can be bookmarked or shared. The Feed's window, counter, and date histogram describe exactly the filtered selection.
- **In the [Graph](/docs/concepts/knowledge-graph/)** — the same hierarchical chips plus an All / Tagged / Untagged toggle.

Tag chips in the **reader header** and the **metadata panel** are links: clicking one opens the Feed filtered by that tag. On **Feed cards** the tag chip is part of the card itself: clicking it (the chip included) opens the note rather than the tag-filtered Feed.

> [!tip] Tags and folders are different axes
> A folder answers "where the note lives"; a tag answers "what it's about." They compose: `folder ∧ tag ∧ text` — a single filtering language in the Feed. The same note can be found through the folder tree and through any of its tags.