Architecture

Last EHR is a thin application layer over a FHIR backend. It is not an EHR, not a system of record, and not a replacement for Medplum, HAPI, or another FHIR server.

Runtime shape

Main modules

• app/api/chat/route.ts: the streaming chat endpoint.
• lib/ai/tools.ts: the four FHIR tools and the system prompt.
• lib/fhir/backend.ts: the FhirBackend interface and backend factory.
• lib/fhir/medplum.ts: Medplum adapter.
• lib/fhir/hapi.ts: plain FHIR R4 REST adapter for local HAPI mode.
• components/demo/demo-chat.tsx: browser chat and approval-card rendering.
• packages/mcp/src: standalone, Medplum-only MCP package with two chart-reading tools.

Tool surface

Reads:

• search_patients
• show_patient_info

Writes:

• add_note
• record_observation

The web app marks write tools with needsApproval: true, so the SDK pauses and the UI renders an approval card before execute runs.

Data boundary

Last EHR stores no chart database of its own.

• Chart data lives in the FHIR backend.
• Chart context read by the agent is sent to the configured model provider.
• The public demo tags writes by browser session so visitors see seed data plus their own writes.
• Backend authentication, tenant isolation, and RBAC belong to the FHIR backend.

Backend boundary

The FhirBackend interface is intentionally small:

• search
• searchResources
• createResource
• deleteResource for seeding/admin tooling only

Adapter authors should keep the interface boring. Do not add app-specific authorization logic to an adapter; rely on the backend's own access controls.