# NACHA Navigator

> Free, private tools and references for US payment files: NACHA (ACH) files, X9.37 image cash letters and BAI2 balance reports. Viewers and builders that run in the browser, file format references, a REST API that generates and validates NACHA files from JSON, and an MCP server for AI agents.

- Files opened in the NACHA, X9.37 and BAI2 viewers are parsed in the browser and never uploaded. The pages' Content-Security-Policy (`connect-src 'self'`) stops a page from sending a file to any other origin.
- The REST API and the MCP server process what a caller sends in memory and never store or log it. Neither one parses a whole payment file; existing files are read in the browser tools.
- No API key or account is needed for the REST API or the MCP server.
- REST API limits: 30 requests per minute per IP address, and request bodies up to 128 KB.
- NACHA Navigator is independent and not affiliated with or endorsed by Nacha. Its references are informational; the Nacha Operating Rules are authoritative.

## Tools

- [NACHA Viewer](https://nacha-navigator.com/index.md): Free NACHA file viewer and ACH file validation tool. Upload, parse, and analyze ACH files field-by-field, generate reversal files, and troubleshoot NACHA format errors. 100% in-browser — your file never leaves your device.
- [ACH Reversal](https://nacha-navigator.com/ach-reversal.md): Reverse an ACH file or selected entries in your browser: transaction codes flipped, REVERSAL description set, the five-banking-day deadline checked. Free.
- [X9 Viewer](https://nacha-navigator.com/x9-viewer.md): Open X9.37 (X9.100-187) image cash letter files in your browser: front and back check images, every record decoded, totals checked. Free; never uploaded.
- [BAI2 Viewer](https://nacha-navigator.com/bai2-viewer.md): Open a BAI2 file in your browser: each account’s balances and transactions, every type code explained, every control total checked. Free, nothing uploaded.
- [NACHA File Generator](https://nacha-navigator.com/nacha-generator.md): Build a valid NACHA ACH file in your browser, from a template or from scratch. Control totals, entry hash and padding are calculated and checked as you type.

## Reference

- [Reference](https://nacha-navigator.com/reference.md): Record layouts, code lists and validation rules for NACHA (ACH) files, BAI2 balance reports and X9.37 image cash letters, plus sample files.
- [NACHA file format](https://nacha-navigator.com/nacha-file-format.md): NACHA file format reference: field positions, lengths and rules for File Header, Batch Header, Entry Detail, Addenda, Batch Control and File Control records.
- [NACHA file errors](https://nacha-navigator.com/nacha-file-errors.md): Why banks reject NACHA files: all 94 checks the NACHA Viewer runs, what each one means and how to fix it, with worked examples.
- [ACH transaction codes](https://nacha-navigator.com/ach-transaction-codes.md): Every ACH transaction code in one table: what the two digits mean, live entries, prenotes, zero-dollar entries, returns and the codes a reversal swaps.
- [BAI2 type codes](https://nacha-navigator.com/bai2-type-codes.md): All 469 BAI2 type codes in one searchable list, with the level and direction of each, plus 10 codes found outside the BAI2 list.
- [BAI2 file format](https://nacha-navigator.com/bai2-file-format.md): How a BAI2 file is built: record order, delimiters and 88 continuations, amounts and funds types, control totals, every record layout and validation check.
- [X9.37 file format](https://nacha-navigator.com/x9-file-format.md): The X9.37 image cash letter format (DSTU X9.37-2003 and X9.100-187): file structure, every record type and field layout, code tables and validation checks.
- [Sample files](https://nacha-navigator.com/sample-files.md): Free sample NACHA (ACH), BAI2 and X9.37 files to download or open in the in-browser viewers, with what each file shows and a line-by-line walkthrough.

## Developers and agents

- [MCP server endpoint](https://nacha-navigator.com/mcp): remote MCP server (Streamable HTTP, no sign-in): NACHA, BAI2 and X9 record layouts, codes and validation rules; validates and generates NACHA files from JSON
- [MCP server](https://nacha-navigator.com/mcp-server.md): Connect an AI agent to the NACHA Navigator MCP server to look up NACHA, BAI2 and X9.37 record layouts and codes, and to check or build NACHA files.
- [NACHA File Generator API documentation](https://nacha-navigator.com/nacha-generator/api.md): Generate or validate NACHA ACH files over HTTP: POST JSON to /api/v1/nacha/generate or /validate. Free, no API key. Request format, field rules and examples.
- [OpenAPI description](https://nacha-navigator.com/openapi.json): OpenAPI 3.1 description of the REST API (generate and validate)
- [API catalog](https://nacha-navigator.com/.well-known/api-catalog): RFC 9727 linkset pointing to the API description and documentation
- [Sample NACHA file: sample-ppd.ach](https://nacha-navigator.com/samples/nacha/sample-ppd.ach): PPD payroll (classic sample)
- [Sample NACHA file: sample-ccd-addenda.ach](https://nacha-navigator.com/samples/nacha/sample-ccd-addenda.ach): CCD vendor payments with remittance addenda
- [Sample NACHA file: sample-ctx.ach](https://nacha-navigator.com/samples/nacha/sample-ctx.ach): CTX payments with EDI 820 remittance
- [Sample NACHA file: sample-returns-noc.ach](https://nacha-navigator.com/samples/nacha/sample-returns-noc.ach): Returns and Notifications of Change
- [Sample NACHA file: sample-with-errors.ach](https://nacha-navigator.com/samples/nacha/sample-with-errors.ach): Validation demo (deliberate errors)
- [Sample BAI2 file: sample-multi-account.bai](https://nacha-navigator.com/samples/bai2/sample-multi-account.bai): Prior-day and same-day report, 5 accounts
- [Sample BAI2 file: sample-simple.bai](https://nacha-navigator.com/samples/bai2/sample-simple.bai): One account, two transactions
- [Sample BAI2 file: sample-with-errors.bai](https://nacha-navigator.com/samples/bai2/sample-with-errors.bai): Report with deliberate errors
- [Sample X9 file: sample-cash-letter.x9](https://nacha-navigator.com/samples/x9/sample-cash-letter.x9): Synthetic X9.37 image cash letter in EBCDIC, with front and back check images

## Optional

- [Use cases](https://nacha-navigator.com/use-cases.md): How payroll teams, banks, treasury, developers, and auditors use NACHA Navigator: validate ACH files, troubleshoot rejected NACHA files, audit batch totals, and generate ACH reversal files — all 100% in your browser.
- [About](https://nacha-navigator.com/about.md): What NACHA Navigator is, how your files stay in your browser, where its rules and codes come from, how the tools are tested and how the site is funded.
- [Terms and conditions](https://nacha-navigator.com/terms.md): Terms and conditions for using NACHA Navigator, the free in-browser NACHA file viewer and ACH file validation tool.
- [Privacy policy](https://nacha-navigator.com/privacy.md): How NACHA Navigator handles your data: ACH, X9 and BAI2 files are processed in your browser and never uploaded. Only anonymous counts and error logs are kept.
- [Full text](https://nacha-navigator.com/llms-full.txt): the Markdown version of every page in one file