# Postern, for agents

Postern is a self-hosted personal context gateway. A human runs it on hardware they own; you connect to THEIR gate, at their address. There is no central Postern endpoint and no Postern cloud.

What you get

One MCP surface over the sectors of a person's life — finance, mail, calendar, contacts, health, home. Reads are served from a local cache in milliseconds; actions dispatch to the source where the source allows them. You correlate across sectors yourself: there are no cross-sector joins, by design.

Connecting

• Endpoint: the owner's gate address + /mcp (Streamable HTTP).
• Local (same machine): connect directly; the owner mints you a key in their Console and grants sectors.
• Remote: the owner exposes their gate through their own tunnel. Hosted agents (claude.ai and similar) use the gate's built-in OAuth bridge: standard discovery + dynamic client registration at the owner's public address.
• Auth: a per-agent bearer key (32 random bytes, base64url), shown to the owner once and stored by the gate only as a hash — or an OAuth token derived from it through the bridge. You never receive, see, or need the owner's provider passwords.
• The config block, verbatim (the owner's Console hands them this; local harnesses paste it into their MCP config):

{
  "mcpServers": {
    "postern": {
      "type": "http",
      "url": "http://<owner-gate-address>/mcp",
      "headers": { "Authorization": "Bearer <your-agent-key>" }
    }
  }
}

• There is no stdio transport on a running gate — the gateway owns its own stdin. Local means the block above with a localhost address.
• A REST mirror serves the reads for tools that do not speak MCP; acting on a source goes through MCP.

The tools

describe_context   what you are granted + per-connection freshness
get_schema         one object's fields, filters, and semantics
query              cache read: filters, fields, time ranges, aggregates
get_record         one record by id
fetch_live         the one read-time path to the source, when freshness matters
list_actions       what the granted sectors let you DO
invoke_action      act on the source; a targeted re-sync reflects the result

Start with describe_context. Read get_schema's notes before composing filters — sign conventions and unit traps live there. Responses are capped: has_more: true means you saw a page, not an answer.

The rules of the gate

• Grants are per-sector and default-deny. You see nothing the owner has not granted; within a grant you request bounded slices, never a dump.
• A refusal is explicit, and every visit — reads, actions, refusals — lands in an append-only ledger the owner reads.
• The owner can revoke your key in one click. Nothing upstream changes; you simply stop resolving.
• Mail bodies are never cached; envelope metadata is served and content is fetched on demand.

No gate yet?

Your human brings one up in minutes on a machine they control:

# pulls the published image, ghcr.io/getpostern/postern
git clone https://github.com/getpostern/postern.git && cd postern
echo "POSTGRES_PASSWORD=$(openssl rand -hex 24)" > .env
docker compose up -d

Then: Console → connect sources → mint you a key → grant sectors. Per-provider field guides: getpostern.com/guides. Source: AGPL-3.0, github.com/getpostern/postern.

raw markdown: /for-agents.md · /llms.txt · getpostern.com