The following VS Code addon helps to visualize a .mermaid file: https://marketplace.visualstudio.com/items?itemName=tomoyukim.vscode-mermaid-editor

It also has a feature to save an .svg image, which be opened in Chrome for a decent pan and zoom experience.

The following are important concepts:

• Card and Field Definition Relationships: There is a subtle distinction between card and fields to consider when creating cards.
• Inheritance: Cards can be extended based upon user's custom needs -- no reinventing the wheel.
• Rendering: Cards can be rendered easily in the browser. Each card renders differently based upon how it is related and what context it exists in.
• Serialization and Deserialization: Cards have to be adapted to a consistent JSON format before being sent over-the-wire to other consumers.
• Computed Fields: Computed fields work too! We can compute on the data that is already contained in a card to build more complex logic.
• Indexing: Indexing powers the re-rendering of cards when it's dependencies get updated.
• Realm: Realms are storage for cards that have their own underlying permissions and indexer.
• Realm Resource Identifiers: How cards, modules, and files are named — including the portable @cardstack/base/ prefix form and how the VirtualNetwork resolves it.
• Search: Every Card is searchable within and across realms.
• Boxel rendering protocol: the render contract every execution tier owes a card — what authored code may rely on, what crosses an execution boundary, and how a card is routed to a trust tier. Status DRAFT: it states main's observed rendering behavior in normative language, and becomes binding when the Direct equivalence oracle is green. Each statement carries an RP-x.y id, and pnpm lint:rp-bijection holds statements and conformance tests to each other.
• Execution runtime wild corpus: the 50-card breadth lane for the execution runtime — real persisted cards compared through a reference Host and a candidate Host, rendered from the executable manifest the smoke runner reads. The corpus validates; a red card opens a conformance test rather than an adapter exception.
• Execution runtime render baseline: the method, environment, and recorded cold/warm render timings that later execution-runtime performance claims are measured against. Local development numbers are diagnostic, not objectives.

• Realm-server health signals: which check answers which question, why an event-loop-gated failure is honest, and what to do when the loop saturates.
• Liveness wedge threshold: set REALM_LIVENESS_WEDGE_MS (milliseconds) to control how long the realm-server's event loop may go without turning before /_liveness reports it wedged; default is 60000 (sized against measured stalls — see the doc), floor 5000. The endpoint is served only when --livenessPort is passed.
• From-scratch indexing timeout: set FROM_SCRATCH_JOB_TIMEOUT_SEC (seconds) to control the from-scratch indexing job timeout and the queue worker cap; default is 3600.