Technical details

1. Register. At load, a plugin registers its roles. A role is namespace.name, and the first plugin to use a namespace owns it.
2. Route. The role names a tier, and you can move it to another. There are seven built-in tiers (quick, balanced, careful, frontier, research, embedding, decision) plus any you make. Each has a limit per call and a budget per month, starting at 1¢ a call and $5 a month for quick, up to $2 and $20 for frontier.
3. Check. Before anything is sent, the most the call could cost is checked against the tier's per-call limit, what's left of its month and the monthly cap across every plugin on the Hub (spendCap()). Note text goes to a cloud provider only once you've said yes to that provider. A call that would go over is refused with a code and a plain message.
4. Send. Provider adapters are built on the Vercel AI SDK (ai 7). If a model fails, the next model on the tier's list is tried, never one you didn't list, and the result says it came from a fallback.
5. Record. Each attempt gets a ledger row: plugin, role, model, tokens, listed cost, billed cost and the note it was about. A call billed well above its listed price is flagged. Prices come from models.dev about once a week; OpenRouter reports the exact billed cost.

// wanted: the Hub API version your plugin was built for
const found = getHub(this.app, wanted);
if (!found.hub) return new Notice(found.message);
found.hub.registerRoles(this.manifest.id, [
  { name: 'mine.summarize', description: 'Summaries of a note', tier: 'quick' },
]);
const r = await found.hub.complete('mine.summarize', messages, { for: file.path });
// r.text, r.usage, r.listedUsd, r.billedUsd, r.servedModel

Refusals are typed. Every refusal is an error with a code (over-ceiling, cap-reached, capability-missing, provider-unavailable, …). A model that can't do what's asked (tools, structured output, images, web search) refuses with a reason instead of being swapped silently.

Tools

Skills

A skill is a note that tells the model how you work. Markdown, Bases and Canvas skills are built in, on kepano/obsidian-skills. Your own come from a vault folder, and plugins add theirs with registerSkills.

The MCP server

MCP is the standard way AI apps share tools. Switch it on and Claude Code, Claude Desktop or Codex can use your plugins' tools, and the skills you mark arrive as prompts. It's the one server for the family; no plugin runs its own.