Architecture#

camt053 is one facade, camt053.services, with four surfaces in front of it and five packages of logic behind it. Every interface (the Python API, the Click CLI, the FastAPI REST API, and the companion MCP and LSP servers) calls the facade, so they behave the same.

 Click CLI    FastAPI REST API    camt053-mcp    camt053-lsp
     \               |                 |              /
      +--------------+-------+---------+-------------+
                             |
                     camt053.services
                             |
     +------------+----------+-----------+----------------+
     |            |                      |                |
  parse/      reversal/                xml/          validation/
  statement   reversal builder    template + the     IBAN, BIC, LEI,
  parser,                         official ISO XSD   JSON Schema
  reason codes

Module	Responsibility
`camt053.parse`	Namespace-agnostic statement parser, return-reason helpers, de-duplication keys, lenient parse reports
`camt053.reversal`	Builds flat reversing-entry records from parsed entries, with deterministic references
`camt053.xml`	Renders the camt.053 and pacs.004 templates, re-serialises statements, validates against the ISO XSDs
`camt053.validation`	IBAN, BIC, LEI, ISO 4217 currency and JSON-Schema validators
`camt053.profiles`	Per-revision rules (`.001.02`, `.001.08`, `.001.13`, `.001.14`) on top of the namespace-agnostic parser
`camt053.compliance`	CBPR+ November 2026 readiness checks and SWIFT X charset cleansing
`camt053.security`	XXE-safe parsing guard and path-traversal-checked output
`camt053.services`	The shared facade backing every interface
`camt053.suite`	The suite’s membership and versioning policy

The flow of one reversal#

services.generate_reversal(xml, reason_code="AC04") parses the statement with defusedxml into a ParsedDocument. The REST API first passes every payload through services.guard_xml (security.xml_guard: byte cap, no inline DOCTYPE or ENTITY); library callers handling untrusted input call it themselves.
The entries carrying the reason code are selected, and reversal.build_reversal_record turns each into a flat record: the credit/debit indicator flipped, RvslInd set, the reason carried in RtrInf, and a reference derived from the original by stable_reversal_reference, so a retry produces the same reference.
xml.generate_xml renders the camt.053.001.14 Jinja template and validates the result against the bundled XSD before returning it. A document that does not validate is never returned.

Where the complexity is#

complexity-baseline.json lists the functions and files over the per-function ceilings. It may only shrink: scripts/check_complexity.py fails when an entry gets worse and when one improves without the baseline being updated.