Form2FHIR

Any clinical form → a valid FHIR Questionnaire.

Paste a blank clinical form, or upload a PDF or a screenshot. An AI agent built on the Claude API turns it into a FHIR R4 Questionnaire (SDC), with questions coded in LOINC. It keeps correcting itself until the Questionnaire passes validation.

The model proposes, the validator decides.

Live demo: form2fhir.vercel.app · Demo only: blank forms, no real patient data. Not a medical device.

How it works

Browser ── POST /api/convert (text | PDF | image) ──► Nuxt server route
   ▲                                                      │ size, type and rate-limit checks
   │ Server-Sent Events: each step, then the result       ▼
   └───────────────────────────────────────────── agent loop (≤ 4 Claude calls)
                                    ┌───────────────────────┴──────────────────────┐
                              search_loinc                               submit_questionnaire
                         NLM Clinical Tables API              server checks ─► HAPI FHIR $validate
                                                              errors go back to Claude to fix

1. Claude reads the form (text, or a PDF / image natively) and calls search_loinc with every question worth coding. The server queries the NLM Clinical Tables LOINC API and remembers every code it returned. For a known instrument (PHQ-9, AUDIT-C…) it also fetches the panel's official questions, with their answers and scores.
2. Claude calls submit_questionnaire with a complete FHIR R4 Questionnaire. The server checks what HAPI can't (every LOINC code must come from step 1; every scored LOINC answer carries its exact score as an ordinalValue; choice items need answer options; no HTML rendering extensions), warns when an item under a panel uses a code that is not one of the panel's questions, then calls HAPI FHIR $validate.
3. Errors go back to Claude as a tool error and it resubmits the whole resource. The run stops when the Questionnaire is valid, or after 4 Claude calls with the last attempt shown as not valid.

Every step streams to the UI, which renders the result with NLM's LHC-Forms, plus the JSON, the codes table and the validator report.

Design choices

• Hand-written agent loop, no framework. About 200 lines in server/lib/agent.ts, so every step can be traced and tested with a scripted fake client.
• The validator decides, and the server enforces the codes. Public HAPI does not check LOINC codes, so the server rejects any code the search did not return. The model can't invent one.
• One POST that streams back. EventSource only supports GET, so the browser reads the text/event-stream body of a fetch POST. No server-side state, which suits serverless.
• Few dependencies. Nuxt, Nuxt UI, the Anthropic SDK and Vitest. LHC-Forms loads from NLM's CDN on demand, pinned and checked with Subresource Integrity. JSON highlighting is a 30-line tokenizer.
• Guardrails for a public demo.
  • Per-IP and daily rate limits, which only count real conversions.
  • Size, type and page caps on uploads, and a token count before any paid call.
  • A 120 s run budget and capped max_tokens and searches.
  • Cross-site requests rejected.
  • Form content is treated as data, never as instructions.

Run locally

cp .env.example .env   # set ANTHROPIC_API_KEY
pnpm install
pnpm dev

Scripts

Command	What it does
pnpm test	Unit tests (offline)
pnpm test:live	Smoke tests against the LOINC search and HAPI FHIR APIs
pnpm typecheck / pnpm lint / pnpm build	Quality gates
node eval/run.ts --url http://localhost:3000	Runs every fixture through the real API (costs API credits)

Evaluation

Five blank forms (eval/fixtures.json lists each one's source and license), run end to end through /api/convert with Claude Sonnet 5.5:

Form	Lang	Valid	Claude calls	LOINC coverage	Code accuracy	Time	Est. cost
Vital Signs Intake	en	✅	2	9/13 (69%)	8/10 (1 wrong)	14.8 s	$0.044
PHQ-9	en	✅	2	10/10 (100%)	10/10	26.5 s	$0.083
Pre-Visit Health Questionnaire (PDF)	en	✅	2	4/11 (36%)	2/4	14.0 s	$0.033
Questionnaire relatif à l'état de santé du sportif mineur (Journal officiel, PDF)	fr	✅	2	1/26 (4%)	0/1	21.8 s	$0.063
Bilan annuel de suivi (diabète de type 2, PDF, 3 pages)	fr	✅	3	16/56 (29%)	15/20	75.7 s	$0.159

5/5 valid · median 21.8 s · total ≈ $0.38 · code accuracy 35/45 (78%), 1 wrong (2026-10-27, eval/results/).

How to read it:

• Valid means the HAPI FHIR $validate operation reported no errors and the server's own checks passed (every LOINC code was returned by a search in the same run).
• Code accuracy compares the agent's codes with an answer key of 45 items (expectedCodes in eval/fixtures.json, each code checked against the LOINC API): correct, wrong (another code) or missing (uncoded). Valid FHIR is not enough: a Questionnaire can pass $validate with the wrong code. Re-scoring the previous run (2026-10-16) gives 37/45 with 2 wrong, among them the PHQ-9 difficulty question coded with the generic 44256-6 instead of the panel's own 69722-7. Since panel searches return the panel's official questions, the PHQ-9 is 10/10 with no wrong code; the agent leaves a few more items uncoded instead. NLM's AUDIT-C definition replaces item 1 (68518-0) with another question, so the agent now also searches each question of an embedded instrument on its own: AUDIT-C item 1 is coded since 2026-10-27. The one wrong code is the respiratory rate coded as "Respiratory rate --resting" (9303-9) instead of 9279-1; the form does not say whether the patient is at rest. Pre-Visit went from 3/4 to 2/4 in this run (pain left uncoded). One run per form, so expect some variance between runs.
• LOINC coverage counts every question item, including ones no terminology would code (name, consultation date, free-text notes, or the French sports questionnaire's custom questions). Codes are only added when a search result clearly matches; an uncoded item is preferred to a wrong code.
• A first run scored 8/56 on the diabetes form because the agent submitted after a single search round. Telling it to always search in English (the LOINC API is English-only), to cover standard measurements systematically and to search embedded instruments (AUDIT-C, PHQ-2) raised it to 18/56 with no wrong codes. Both runs are kept in eval/results/.

Attribution

• This material contains content from LOINC. LOINC is copyright © Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee and is available at no cost under the license at loinc.org/license. LOINC searches use the NLM Clinical Tables API.
• FHIR® is the registered trademark of HL7 and is used with the permission of HL7.
• Questionnaire preview by LHC-Forms (U.S. National Library of Medicine). Validation by the public HAPI FHIR test server.
• Built with the Claude API.

License

Code: MIT. The forms used as examples and eval fixtures keep their own licenses, listed in eval/fixtures.json (PHQ-9: Pfizer, free to reproduce; the French sports questionnaire: an official text published in the Journal officiel; the other forms were written for this project and are CC0).