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FHIRBuildersThe home for FHIR builders

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Healthcare AI Builders Wiki

A living, LLM-curated map of what every healthcare AI builder should know — FHIR core, implementation guides, terminology, US regulation, AI patterns, and the active CMS initiatives + Slack communities where the work is happening. Inspired by Karpathy's LLM-wiki concept — an evolving graph, not a static encyclopedia.

Graph view Log Source

How this wiki works. Topics are nodes with summaries + external links + status (seed → draft → stable). Edges encode dependencies (US Core depends-on FHIR R4), production relationships (CMS-0057 → DaVinci PAS), and discussion channels (CMS Health Tech Slack discusses NPD). See the whole thing spatially in the graph view. The graph is meant to grow — every change lands in the log so future you (or a forking team) can see what was added when and why. Fork the src/lib/wiki/module to build your own — see the template guide.

Live signal

Recent activity from connected channels — automatically ingested from the FHIRBuilders Slack via cron, plus manually-curated digests from the CMS Health Tech Ecosystem and Health Tech Nerds workspaces.

No signals yet. The cron fires daily at 14:00 UTC — first run lands tomorrow morning ET.

FHIR Core

Versions, REST API, profiles, SMART, bulk data.

6 topics

FHIR — Fast Healthcare Interoperability Resources

HL7's modern interoperability standard. Resource-based, REST-first, JSON-default. The default substrate for almost every healthcare AI app that touches real clinical data.

FHIR Versions — R4, R4B, R5, R6

R4 is the production standard most US implementers use. R5 ships profile-level breaking changes. R6 (2026+) is starting to land in early implementations.

GET / POST / PUT / DELETE against /[Resource]/[id]. Search via /[Resource]?param=value. Bundles for atomic batches/transactions. Capability statement at /metadata.

Profiles + Extensions

Profiles narrow base FHIR resources for a specific use case. Extensions add fields the base spec doesn't have. Implementation Guides bundle profiles + value sets + examples.

OAuth 2.0 + OpenID Connect profile for FHIR apps. Defines launch flows (standalone, EHR-embedded), scopes (patient/*.read, user/*.write), and the capability statement extensions.

Bulk Data — FHIR Async Export

FHIR's $export operation for population-level data. NDJSON output, signed URLs, asynchronous. The backbone of payer / provider bulk handoffs and CMS-mandated APIs.

Implementation Guides

US Core, DaVinci, Blue Button, SDOH, mCODE.

13 topics

Minimum FHIR profile set ONC requires US-certified EHRs to expose. The baseline every US healthcare app should design against.

Blue Button 2.0 (CMS)

CMS's FHIR API exposing Medicare claims data to ~60M beneficiaries via patient-authorized apps. The reference implementation for patient-mediated claims exchange.

CARIN Blue Button IG

Profile set for consumer-directed payer claims data. The blueprint payers must implement under CMS Interoperability Rule for member-app access to claims.

DaVinci PDex — Payer Data Exchange

Payer-to-payer FHIR exchange of member clinical + claims history at plan change. Required by CMS-9115 for participating payers.

DaVinci DTR — Documentation Templates and Rules

Embeds payer documentation rules into the provider workflow at point-of-order. The 'fill out the prior auth form using the EHR data you already have' pattern.

DaVinci CRD — Coverage Requirements Discovery

CDS Hooks pattern that asks the payer 'is this order covered, and what documentation is needed?' at the moment of ordering.

DaVinci PAS — Prior Authorization Support

FHIR-native prior auth submission. Required for some payer scenarios under CMS-0057 ePA Final Rule.

DaVinci HRex — Health Record Exchange

Foundation for payer/provider FHIR exchanges. Defines $member-match and the operations that PDex, CDex, etc. build on.

DaVinci CDex — Clinical Data Exchange

Provider-to-payer clinical attachments via FHIR (Task + DocumentReference). Replaces faxing chart notes for claims attachments.

SDOH Clinical Care IG

Profile set for social determinants of health — screening, observation, intervention, referral. The substrate for FHIR-native depression / SDoH workflows (a Cohort 00 theme).

mCODE — Minimal Common Oncology Data Elements

Standard FHIR profiles for cancer care — diagnosis, staging, treatment, outcomes. The substrate for oncology AI work.

Structured Data Capture (SDC)

FHIR profile for forms: Questionnaire + QuestionnaireResponse with prepopulation from FHIR data + extraction back to discrete resources. The pattern behind every FHIR-native intake form.

SMART App Gallery

Public catalog of SMART-on-FHIR apps. Once your Cohort 00 build is SMART-launched + reviewed, list here for health-system discovery.

Terminology

SNOMED, LOINC, RxNorm, ICD-10, CPT, UCUM.

8 topics

Clinical terminology used for conditions, procedures, body sites, findings. ~360K active concepts. The US edition is free-to-use; international edition requires SNOMED International license.

Universal codes for labs, vitals, clinical observations, and surveys. Free, maintained by Regenstrief.

US medication terminology — normalizes drug names across NDC, brand, generic. Used in MedicationRequest.medicationCodeableConcept.

US clinical diagnosis codes used for billing + claims. Often paired with SNOMED in Condition.code (claims-aligned use cases).

CPT — Current Procedural Terminology

AMA-owned procedure codes used for billing. Required for claims + many quality measures.

Healthcare Common Procedure Coding System — supplements CPT for Medicare/Medicaid (durable equipment, ambulance, etc.).

UCUM — Units of Measure

Code system for units. `mm[Hg]`, `mg/dL`, `L/min`. Used with LOINC in Observation.valueQuantity.unit.

Terminology Services

$lookup / $expand / $validate operations against ValueSets and CodeSystems. Run your own or use SNOMED Snowstorm, NLM VSAC, Ontoserver, Aidbox terminology.

Data Quality + Measures

Validation, CQL, SQL-on-FHIR, digital quality measures.

6 topics

FHIR Validation

Server $validate, HL7 Validator CLI, or in-app validation against profiles. Required before claiming conformance with US Core, DaVinci, etc.

FHIRspective — Data Quality Analyzer

Eugene's open data-quality analyzer for FHIR bundles. Surfaces conformance issues, profile mismatches, terminology binding gaps.

CQL — Clinical Quality Language

Author-once quality-measure logic that runs against FHIR data. The substrate for HEDIS, eCQMs, DTR rules.

Map FHIR resources to flat columnar tables via ViewDefinition. Run measures + analytics with normal SQL instead of CQL engines.

FHIR ViewDefinition

Portable spec mapping FHIR resources to flat columns. The contract layer in SQL-on-FHIR. Eugene maintains a public builder + library.

Digital Quality Measures (dQMs)

CMS's term for FHIR + CQL-based quality measures (replacing HQMF + QRDA). The future of MIPS, HEDIS, etc.

Regulation (US)

HIPAA, Cures Act, info blocking, CMS-9115, CMS-0057, TEFCA.

8 topics

US Privacy + Security Rules for Protected Health Information. Compliance is a deployment concern, not a code concern — but you must understand BA obligations before going to prod.

21st Century Cures Act

Landmark 2016 law. Authorized ONC's Information Blocking rule + the API certification criteria (US Core + Bulk Data) every certified EHR must expose.

Information Blocking Rule

ONC's rule prohibiting healthcare actors (providers, EHRs, HIEs) from blocking electronic health information exchange. Enforcement live since 2024.

ONC Certification (HTI-1/2)

ONC's certification framework for EHRs. HTI-1 (2023) brought US Core 3.1.1+, decision support transparency. HTI-2 (2025+) adds Bulk FHIR, patient app endpoints, AI transparency requirements.

CMS-9115-F — Interoperability and Patient Access

CMS final rule requiring payers (Medicare Advantage, Medicaid, CHIP, QHPs) to expose patient + provider + payer-to-payer FHIR APIs. The reason CARIN Blue Button and DaVinci PDex exist.

CMS-0057-F — Prior Authorization API

2024 CMS rule requiring payers to expose FHIR-based prior auth APIs (CRD, DTR, PAS) and disclose PA metrics. Phased compliance through 2027.

Trusted Exchange Framework and Common Agreement. The federal network-of-networks for health data exchange. QHINs are the on-ramps; treaty-level rules govern data flow between them.

QHIN — Qualified Health Information Network

On-ramp networks to TEFCA. eHealth Exchange, CommonWell, Epic Nexus, Carequality, Health Gorilla, KONZA, MedAllies are designated QHINs.

AI · Healthcare

LLMs, agent loops, MCP, Claude Code, prompt-injection in clinical workflows.

6 topics

LLMs in Healthcare

Patterns where LLMs help: clinical scribes, prior auth automation, patient intake, terminology mapping, quality measure narration. Patterns where they don't: deterministic clinical decisions, autonomous prescribing.

Agent Loops over FHIR

Tool-using LLM agents reading/writing FHIR via REST. Loop pattern: read context → reason → call FHIR tool → observe → repeat. Where Claude Code + MCP fits.

MCP — Model Context Protocol for Healthcare

Anthropic's open protocol for connecting LLM agents to external tools/data. Natural fit for FHIR: one MCP server exposes Patient.read, Observation.search, etc. Eugene's HealthClaw + Cohort 00 build on this.

HealthClaw + HealthClaw Guardrails

Open security layer between AI agents and clinical data. PHI redaction, MCP tool gating, FHIR R4/R6 support. Eugene's project.

Claude Code + FHIR

Pattern: Claude Code as the IDE-resident agent that scaffolds a FHIR-reading app, wires MCP servers for live tools, and ships to Vercel. The Cohort 00 backbone.

Prompt Injection in Clinical Workflows

Untrusted clinical text (notes, claims, intake forms) can include prompt-injection payloads. Pattern: never let raw clinical text drive agent tool calls without an allow-list + structured output check.

CMS Initiatives

NPD modernization, Blue Button rebrand, ePA, dQM.

4 topics

NPD — National Provider Directory

CMS-led modernization of the national provider directory (replacing NPPES). Eugene's AINPI project tracks the ecosystem players + FHIR-based architecture.

Open analysis of the CMS health tech ecosystem + NPD modernization effort — players, standards, FHIR architecture. Eugene's project.

CMS Blue Button — Rebrand + Modernization

CMS announced (2025) a rebrand + modernization of Blue Button 2.0. Watch for new branding, expanded data sources (claims + clinical), updated API surface.

CMS Health Tech Ecosystem (program)

CMS's umbrella for the open-innovation initiatives — NPD, Blue Button modernization, ePA, dQM. Coordinated via the CMS Health Tech Ecosystem Slack (see communities).

Communities + Sources

CMS Health Tech Slack, HTN, HL7 FHIR, OOP, DevDays.

8 topics

CMS Health Tech Ecosystem Slack

Enterprise Slack where CMS staff + the broader health-tech ecosystem coordinate on NPD, ePA, Blue Button, dQM and other CMS-driven open-innovation initiatives.

Health Tech Nerds (HTN) Slack

~25K+ member community of healthtech operators, founders, investors, and engineers. The other watering hole — broader than CMS, deeper on industry signal.

Out of Pocket Health

Nikhil Krishnan's healthtech publication + community. Pizza newsletters, Ship It summit, curated cohorts. Eugene's FHIR IQ Cohort 00 borrows the OOP operating system.

Eugene's platform for building, sharing, and collaborating on AI-powered FHIR apps. Hosts the Cohort 00 experience, the sandbox, Problem Board, OpenClaw skills.

FHIR IQ + Out of the FHIR podcast

Eugene's brand. The semantic intelligence layer for healthcare data (product), the Out of the FHIR podcast (content), and the cohort program (training).

HL7 FHIR Community + chat.fhir.org

Official FHIR community on Zulip (chat.fhir.org). Sub-streams by IG (#argonaut, #davinci, #us-core, #payer/provider). The reference forum for FHIR spec questions.

Annual hands-on FHIR conferences (Amsterdam, Boston). Tutorials + Connectathon + speaker tracks. Eugene records Side Chats here with Firely.

FHIR Connectathons (HL7 + CMS)

Three-day hands-on events where implementers test FHIR profiles against real reference servers. HL7 runs WGM connectathons; CMS runs an annual one (July) plus the FHIR-at-Scale Taskforce track.

Wiki v0.1.0 · last updated 2026-06-05 · curated for FHIRBuilders + Cohort 00.