---
name: cyclone-edi
description: "Cyclone EDI parser/validator conventions (837P/835/999/270/271/277CA/TA1). Use when: adding or changing a parser, adding a validator rule (R010/R020/R100/R200-R210/R835_*/NPI Luhn/EIN/CAS), or mapping a new CAS adjustment reason code."
---

# cyclone-edi

Cyclone parses seven X12 EDI transaction types (837P, 835, 999, 270, 271, 277CA, TA1) into typed Pydantic models, then runs per-claim / per-batch validator rules that surface as R-coded `ValidationIssue` records. This skill codifies the conventions so new parsers and rules stay consistent with the seven that already exist.

As of this writing: **7 parser modules** under `backend/src/cyclone/parsers/parse_<edi>.py`, **~25 per-claim rules** numbered `R010`–`R100` and `R200`–`R210` in `validator.py`, plus a parallel set of **835-specific rules** prefixed `R835_*` in `validator_835.py`. The next increment is **SP22**.

## When to use

- **Adding or changing a parser.** You are about to touch `backend/src/cyclone/parsers/parse_<edi>.py` or its paired `models_<edi>.py` and need the orchestrator signature, the segment walker convention, and the re-export in `parsers/__init__.py`.
- **Adding a validator rule.** You are writing a new `_rule_R<n>_<name>` (or `_r<n>_<name>` per the existing snake-case style) and need the rule signature, the R-code numbering scheme, and the `ValidationIssue` shape.
- **Wiring a new CAS / CARC code.** The 835 carries Claim Adjustment Reason Codes in `CAS` segments; the lookup lives in `backend/src/cyclone/parsers/cas_codes.py` and the UI reads through `claim_status_label()`.
- **Debugging a parse failure on a prodfiles sample.** You dropped a real EDI file into `docs/prodfiles/<source>/` and the parser is choking — load this skill to confirm the tokenizer path, the orchestrator entry point, and which fixture in `backend/tests/fixtures/` matches the transaction type.

## Conventions

1. **Parser signature.** Every parser module exports exactly one public entry function. Two flavors coexist in the codebase:
   - `parse(text: str, *, input_file: str = "") -> <TypedResult>` — used by `parse_270.py:337`, `parse_271.py:356`.
   - `parse(text: str, payer_config: <PayerConfig>, input_file: str = "") -> <TypedResult>` — used by `parse_837.py:319` and `parse_835.py:459` because both need payer-specific config to validate segments against.
   - `parse_<edi>_text(text: str, *, input_file: str = "") -> <TypedResult>` — the legacy name-suffixed form, still in use at `parse_ta1.py:143`, `parse_999.py:220`, `parse_277ca.py:280`. The `<TypedResult>` is always a Pydantic model from `models_<edi>.py` (or co-located `models.py` for 837P).
2. **Segment walk.** Parsers consume `backend/src/cyclone/parsers/segments.py` — there are exactly three public pieces: `Delimiters` (frozen dataclass holding the four ISA-derived separators), `_detect_delimiters(isa_segment)` (private), and `tokenize(text) -> list[list[str]]` (returns ISA prepended as the first segment). Parsers then index into the `list[list[str]]` directly — there is **no** `Segment` / `Loop` / `next_segment` helper class. Whole-document problems (missing ISA, wrong transaction set) raise `CycloneParseError`; per-segment problems on acks (999/277CA) are surfaced on the result, not raised.
3. **Validator rules.** Numbered rules live in `backend/src/cyclone/parsers/validator.py` (for 837P — R010–R100 general + R200–R210 SP9 CO MAP / HCPF naming) and `backend/src/cyclone/parsers/validator_835.py` (for 835 — names prefixed `R835_*` because the same numeric space would collide with 837P). Each rule is a function `_r<n>_<name>(claim: ClaimOutput, cfg: PayerConfig) -> Iterable[ValidationIssue]` registered in the module-level `_RULES` list and run by `validate(claim, config)`. Issues carry the rule name as a stable string (`rule="R021_npi_checksum"`) — the R-code **is** how the UI surfaces the error, so never invent an unnumbered rule.
4. **NPI / EIN / CAS format logic.** Identity-format checks live in their own modules — never duplicate them in a parser or validator:
   - `backend/src/cyclone/npi.py` — `is_valid_npi(npi)` runs the Luhn checksum with the `80840` NPPES prefix; `is_valid_tax_id(ein)` enforces `XX-XXXXXXX` (or 9 raw digits).
   - `backend/src/cyclone/parsers/cas_codes.py` — `reason_label(group, reason)` and `all_known_codes()` for the CARC lookup; snapshot date is exported as `LAST_UPDATED`.
   - `backend/src/cyclone/parsers/models_271.py` — `SERVICE_TYPE_CODES` + `service_type_description()` for 271 EB benefit codes.
5. **Prodfiles reuse.** When adding a parser for a new transaction type, ship at least one fixture in `backend/tests/fixtures/<edi>/<sample>.txt` (the existing 13 fixtures are **flat** at the top level of `fixtures/` — no per-test subdirectories). Copy from `docs/prodfiles/<source>/<file>.txt`; never reach into `docs/prodfiles/` from a test. The matching test should declare the path as a module-level `Path` constant.

## Patterns

### Minimal `parse_<edi>.py` — using `segments.py`, exporting `parse_ta1_text`

Taken from `backend/src/cyclone/parsers/parse_ta1.py:1-29` (the smallest parser — TA1 is just ISA + TA1 + IEA). The same skeleton scales to every other EDI type by adding `_consume_<segment>` helpers.

```python
"""Parse an X12 TA1 (Interchange Acknowledgment) file.

Whole-document problems (missing ISA, no TA1) raise CycloneParseError.
"""
from __future__ import annotations

import logging
from datetime import date

from cyclone.parsers.exceptions import CycloneParseError
from cyclone.parsers.models import BatchSummary, Envelope
from cyclone.parsers.models_ta1 import ParseResultTa1, Ta1Ack
from cyclone.parsers.segments import tokenize

log = logging.getLogger(__name__)


def _parse_yyyymmdd(s: str) -> date | None:
    """Parse an 8-digit CCYYMMDD string. Returns None on bad input."""
    ...


def _build_envelope(segments: list[list[str]], input_file: str) -> Envelope:
    """Build the envelope from ISA. TA1 has no GS/ST — just ISA → TA1 → IEA."""
    ...


def _consume_ta1(segments: list[list[str]], idx: int) -> tuple[Ta1Ack, int]:
    """Read a TA1 segment and return a Ta1Ack. Returns (model, next_idx)."""
    ...


def parse_ta1_text(text: str, *, input_file: str = "") -> ParseResultTa1:
    """Parse a complete TA1 document and return a ParseResultTa1."""
    segments = tokenize(text)
    envelope = _build_envelope(segments, input_file=input_file)
    ta1_idx = next(
        (i for i, seg in enumerate(segments) if seg[0] == "TA1"), None,
    )
    if ta1_idx is None:
        raise CycloneParseError("No TA1 segment found")
    ta1, _ = _consume_ta1(segments, ta1_idx)
    ...
    return ParseResultTa1(envelope=envelope, ta1=ta1, summary=summary, ...)


__all__ = ["parse_ta1_text"]
```

The orchestrator pattern is the same in every parser: `tokenize` → `_build_envelope` → segment consumers in order → wrap into a `ParseResult<EDI>` model. The Pydantic result is what the API / store layer consumes.

### A validator rule — `_r<n>_<name>` registered in `_RULES`

Taken from `backend/src/cyclone/parsers/validator.py:23-66` (the canonical R010–R100 block).

```python
from collections.abc import Iterable
from cyclone.parsers.models import ClaimOutput, ValidationIssue
from cyclone.parsers.payer import PayerConfig

NPI_RE = re.compile(r"^\d{10}$")
Rule = Callable[[ClaimOutput, PayerConfig], Iterable[ValidationIssue]]


def _r020_npi_format(claim: ClaimOutput, _: PayerConfig) -> Iterable[ValidationIssue]:
    if claim.billing_provider.npi and not NPI_RE.match(claim.billing_provider.npi):
        yield ValidationIssue(
            rule="R020_npi_format",
            severity="error",
            message=f"Billing provider NPI must be 10 digits, got {claim.billing_provider.npi!r}",
        )


def _r021_npi_checksum(claim: ClaimOutput, _: PayerConfig) -> Iterable[ValidationIssue]:
    """SP20: validate the billing-provider NPI's Luhn check digit."""
    npi = claim.billing_provider.npi
    if not npi or not NPI_RE.match(npi):
        return  # R020 already flagged the format — skip silently.
    try:
        from cyclone.npi import is_valid_npi
    except ImportError:
        return
    if not is_valid_npi(npi):
        yield ValidationIssue(
            rule="R021_npi_checksum",
            severity="warning",
            message=f"Billing provider NPI {npi!r} fails Luhn checksum (likely typo)",
        )


_RULES: list[Rule] = [
    _r010_clm01_present,
    _r011_total_charge_positive,
    _r020_npi_format,
    _r021_npi_checksum,
    # ... R030, R031, R032-R035, R050, R060, R070, R100, R200-R210
]
```

For 835 rules, prefix the rule string with `R835_` (e.g. `R835_BPR01_handling_code_allowed`) and target the `ParseResult835` model instead of `ClaimOutput` — see `backend/src/cyclone/parsers/validator_835.py:38-79`.

### A test that uses a prodfiles fixture

Taken from `backend/tests/test_api_999.py:53-72`. The autouse `conftest.py` already provides a per-test SQLite DB; most tests just add a `client` fixture and reference the fixture path as a module-level constant.

```python
"""Tests for the FastAPI surface in cyclone.api for the 999 endpoint."""
from __future__ import annotations

from pathlib import Path

import pytest
from fastapi.testclient import TestClient

from cyclone.api import app

# Fixture reference — flat, module-level Path constant. NEVER reach into
# docs/prodfiles/ from a test; the fixtures/ dir is the test-consumed surface.
ACCEPTED = Path(__file__).parent / "fixtures" / "minimal_999.txt"
REJECTED = Path(__file__).parent / "fixtures" / "minimal_999_rejected.txt"


@pytest.fixture
def client() -> TestClient:
    return TestClient(app)


def test_parse_999_endpoint_happy_path(client: TestClient):
    text = ACCEPTED.read_text()
    resp = client.post(
        "/api/parse-999",
        files={"file": ("minimal_999.txt", text, "text/plain")},
        headers={"Accept": "application/json"},
    )
    assert resp.status_code == 200, resp.text
    body = resp.json()
    assert body["ack"]["ack_code"] == "A"
```

For pure-unit parser tests (no API), the same path is reused — see `backend/tests/test_parse_837.py:8` (`FIXTURE = Path(__file__).parent / "fixtures" / "minimal_837p.txt"`).

## Anti-patterns

- **Don't re-parse raw X12 strings inside validators.** Always parse first into the typed `ParseResult<EDI>` / `ClaimOutput`, then validate against that. Validators index into the model fields (or `claim.raw_segments` for spot-checks of specific segment presence) — they never call `tokenize` again. R034's `REF*G1` presence check (`validator.py:104-107`) is the only place that legitimately touches `raw_segments`, and it does so to confirm a single segment exists.
- **Don't bake payer-specific logic into the generic parser.** Payer variations live in `backend/src/cyclone/parsers/payer.py` (`PayerConfig`, `PayerConfig835`) and `backend/src/cyclone/payers.py` (the YAML loader from `config/payers.yaml`). Parsers accept the config as an argument; rules read it from the `cfg` parameter. A new payer never requires a new parser file — extend the config and add / adjust an R-code rule.
- **Don't add a validator rule without an R-code.** The `rule="R<n>_<name>"` string is the stable identifier the UI greys out, the API returns in `errors[].rule`, and tests assert against. Inventing a rule without an R-code (or reusing an R-code with new semantics) breaks the operator workflow. New SP-N increments reserve their R-code range up front (SP9 reserved R200–R210, SP20 added R021) and document it in the spec.

## Related skills

- **`cyclone-store`** — load when the increment changes how a parsed `ClaimOutput` / `ParseResult<EDI>` is persisted (`store.py` write path, `<entity>_written` events).
- **`cyclone-api-router`** — load when the increment adds or changes an HTTP endpoint that surfaces a parsed result (e.g. `/api/parse-999`, `/api/parse-837`, `/api/parse-835`).
- **`cyclone-tests`** — every parser addition ships a fixture in `backend/tests/fixtures/` and a pytest case; load this skill for the fixture-drop-in and autouse-conftest rules.
- **`cyclone-cli`** — load when the increment adds a CLI subcommand. The `cyclone parse-837 <file>` and `cyclone parse-835 <file>` smoke commands at `backend/src/cyclone/cli.py:77,151` are the parser-level smoke tests; the `validate-npi` and `validate-tax-id` commands exercise the format helpers.
- **`cyclone-spec`** — load when the SP-N spec for the increment introduces a new R-code range or a new transaction type; the spec's `## Decisions` section is where the R-code reservation gets locked in.
