SyncLinks & Fan-out

SyncLink

A SyncLink is a directed mapping from a source capability to a target capability:

source_app.source_capability ──▶ target_app.target_capability

Each link carries a wcp_id — a stable identifier for the synced entity (e.g. a note, a row, a page).

Fan-out

Fan-out means one source writes to multiple targets simultaneously. In WCP, fan-out is achieved by creating multiple SyncLinks from the same source:

obsidian:note_abc ──▶ notion.write_page
obsidian:note_abc ──▶ sheets.append_row
obsidian:note_abc ──▶ slack.post_message

A single wcp sync run iterates all active SyncLinks. The source is read once and written to all targets.

Creating SyncLinks

Via the API:

curl -X POST http://localhost:8000/api/links \
  -H "Content-Type: application/json" \
  -d '{
    "wcp_id": "obsidian:note_abc",
    "source_app": "obsidian",
    "source_capability": "read_note",
    "target_app": "notion",
    "target_capability": "write_page"
  }'

Repeat for each additional target.

Link States

State	Meaning
active	Included in every sync run
paused	Skipped during sync, preserved for later
error	Last sync failed; will retry on next run

Syncable Pairs

The /api/capabilities/syncable-pairs endpoint returns all valid source→target combinations based on registered capabilities:

[
  {
    "source": {"app": "obsidian", "capability": "read_note"},
    "target": {"app": "notion", "capability": "write_page"}
  }
]

Use this to build the link creation UI — only show pairs that actually make sense.