Reference

This section is the precise spec an agent executes against — the catalogue of cairn's wire surface. cairn provides fourteen MCP tools and one query language, and everything an agent can ask or change goes through them. Because an agent consumes it directly, the site serves these pages as Markdown and an llms.txt index as well as HTML; each tool, operator, view, and enum has a stable anchor, every returned and error string is copied from source, and the pages are written to be read out of order and deep-linked.

Every call carries a capability gate in its metadata — :cairn/observe, :cairn/write, or :cairn/read — and this section tells you which gate each tool sits behind. Reads, writes, and capabilities explains why the boundary is drawn at the capability rather than the tool name.

Pages

• MCP tools — the fourteen tools (one observe, eight writes, five reads), each with its parameters, capability gate, returned text, and verbatim errors.
• The TQ query language — TQ's sources, pipeline steps, predicates, set algebra, reflection, and the one dynamic gate that separates task_query from task_query_write.
• Built-in and user-defined views — the ten named views cairn ships, each with its exact TQ source text, and how a user view shadows a built-in until you (undefine!) it.
• Edges, statuses, and fields — the closed vocabularies: three edge types, five statuses, eleven typed fields, and the reflective sources that read them back from the store.

For the command-line surface — the six slash commands under a kli host and serving cairn over kli mcp-serve cairn — see Commands & Serving. For what the nouns mean before you call them, start at Concepts.