What we capture, and what we don't.

What capture does

When Line9 successfully parses a diagram, the canonicaliser produces a structural fingerprint: nodes relabelled in canonical order, edges with directions and endpoints, node shape categories, and subgraph nesting. That fingerprint is written to a private corpus so the project owner can re-render entries against the current Line9 and find layouts that need work. Separately, a small render event is recorded — outcome, timing, viewport, theme — so error rates and performance are visible.

What never leaves the browser

The Mermaid source you type, all node and edge labels, your node IDs, comments, colours, and any other free-form content stay on your device. The wire format structurally cannot carry them — there is no source field, no labels field, no free-text error message. The one exception is one you make yourself: if a diagram fails to parse, the feedback panel lets you tick a box to send us the source. The privacy policy, § 8, lists exactly what that report contains.

Topology corpus fields

Each topology write is a JSON document with exactly these fields:

• topology_key Content hash of the canonical structural form.
• topology_key_version Version of the canonicalisation algorithm that produced the key.
• canonical_graph Anonymous graph: vertices in canonical order, edges with directions and endpoints, node shape categories, subgraph nesting.

Render event fields

Dimensions:

• render_status success, layout_error, unknown_error, or parse_error (whole-source arrivals only).
• render_error_code Enumerated failure category from @line9/core when status is not success.
• diagram_type Parsed diagram kind (e.g. flowchart, sequenceDiagram).
• theme Selected diagram theme.
• orientation portrait or landscape, as the viewer rendered it.
• line9_version Version string of @line9/core at render time.
• topology_key Structural identifier; absent for diagram kinds the canonicaliser does not yet handle.
• topology_key_version Canonicaliser version; present whenever topology_key is.
• referrer_host Hostname of document.referrer only — no path, no query.
• arrival_origin How the source arrived (paste, share_hash, published, example). Present only on parse_error.

Metrics:

• render_duration_ms Wall-clock time from parse start to render end.
• viewport_width CSS pixels of the rendering viewport.
• viewport_height CSS pixels of the rendering viewport.
• spacing_scale Multiplier on inter-node and edge spacing.
• node_scale Multiplier on node size.

Topology corpus opt-out

Product analytics id

Line9 uses PostHog (EU cloud, first-party proxy) for product usage — page views and curated events such as render/export/share. Diagram source and labels never leave the browser for this path. We ask before setting a durable first-party id. Accepting lets us stitch sessions across visits; declining, or not choosing, keeps the id memory-only while in-memory analytics continues. See the privacy policy § 9.