cobol-safe-translator

Translate COBOL to Python. Zero dependencies. Works offline.

Produces valid Python from real enterprise COBOL — tested on 5,288 files across 32 projects with 100% syntax and validation pass rate. Handles the structural heavy lifting of mainframe migration so developers and AI agents can focus on business logic and middleware integration.

Ships with an MCP server for AI coding assistants and a CLI for direct use.

This tool generates skeleton code that requires review. COBOL data semantics (fixed-point arithmetic, string padding, FILE STATUS) are preserved through runtime adapters, but middleware (DB2, CICS, MQ, VSAM) must be wired up separately. Every untranslated construct is marked with TODO(high).

Why this exists

COBOL runs an estimated $3 trillion in daily financial transactions. The engineers who maintain it are retiring, and the systems they built are locked behind proprietary middleware and decades-old documentation.

This tool exists to make those systems readable, translatable, and migratable — without needing an IBM contract or a mainframe consultant. Open source, offline, no vendor dependency.

Run it against any .cob/.cbl/.cobol file and get:

• A runnable Python skeleton with COBOL semantics preserved
• EXEC SQL code generation (DB-API 2.0 with parameterized queries)
• A sensitivity report flagging SSNs, balances, and PII
• A token-efficient LLM brief for AI agents to finish the migration
• An interactive test that validates and executes the translation

Install

pip install cobol-safe-translator   # zero runtime dependencies

# Or from source
git clone https://github.com/IronAdamant/PythonBol-Translator.git
cd PythonBol-Translator && pip install -e ".[dev]"

Requires Python 3.11+. No pip dependencies at runtime. Cross-platform (Linux, macOS, Windows). Works fully offline.

Quick start

# Translate a single file
cobol2py translate PAYROLL.cob

# Translate a directory recursively with copybook paths
cobol2py translate ./src/ --recursive --copybook-path ./cpy --output ./out

# Validate generated Python (syntax + import + instantiation)
cobol2py translate PAYROLL.cob --validate

# Full pipeline test (translate + validate + execute)
cobol2py test PAYROLL.cob

# Batch test an entire directory
cobol2py test ./src/ --recursive --timeout 30

# Generate analysis reports (Markdown + JSON)
cobol2py map PAYROLL.cob

# Generate LLM translation brief
cobol2py prompt PAYROLL.cob > brief.md

# Triage a project — categorize TODOs for team assignment
cobol2py triage ./src/ --recursive --output ./triage --json

# Translate with middleware interface stubs (DB2/CICS/DLI/MQ)
cobol2py translate ./src/ --recursive --package --stubs

Use with AI agents

MCP Server (Claude Code, Cursor, Windsurf, etc.)

{
  "mcpServers": {
    "cobol-translator": {
      "command": "python",
      "args": ["-m", "cobol_safe_translator", "--mcp"]
    }
  }
}

The MCP server exposes 7 tools: translate_cobol, analyze_cobol, generate_brief, list_sensitivities, discover_cobol_files, translate_directory, triage_project.

LLM Prompt Brief

cobol2py prompt PAYROLL.cob > brief.md
# Feed brief.md to any LLM and ask it to fill the TODOs

The prompt brief is 3-4x more token-efficient than raw COBOL source, containing only what the LLM needs: data structure, control flow, sensitivities, and the Python skeleton.

Supported COBOL features

Fully translated to Python

| Category | Features | |----------|----------| | Data Division | PIC clauses (9/X/A/S/V/P/edited), levels 01-49/77/88, OCCURS (multi-dimensional), REDEFINES, WORKING-STORAGE, FILE SECTION, LINKAGE SECTION, LOCAL-STORAGE, REPORT SECTION, SCREEN SECTION | | Data types | USAGE COMP/COMP-3/BINARY (CobolDecimal), COMP-1/COMP-2 (float), COMP-5 (int), INDEX (int), DISPLAY (default) | | Data attributes | EXTERNAL, GLOBAL, JUSTIFIED RIGHT, BLANK WHEN ZERO, OCCURS DEPENDING ON (guard), SYNCHRONIZED | | Arithmetic | ADD, SUBTRACT, MULTIPLY, DIVIDE (INTO/BY/GIVING/REMAINDER), COMPUTE (complex expressions), ON SIZE ERROR, ROUNDED (ROUND_HALF_UP) | | Control flow | IF/ELSE (multi-line + inline), EVALUATE TRUE/variable/ALSO with WHEN THRU (range comparison), PERFORM (simple/UNTIL/TIMES/VARYING/THRU), nested loops, GO TO (method call + return, ALTER dynamic dispatch), GO TO DEPENDING ON, EXIT PERFORM | | String ops | STRING (DELIMITED BY, WITH POINTER), UNSTRING (multi-delimiter, WITH POINTER, TALLYING), INSPECT (TALLYING/REPLACING/CONVERTING with BEFORE/AFTER INITIAL), MOVE (simple/ALL/CORRESPONDING/FUNCTION/group-level) | | Table ops | SEARCH/SEARCH ALL, SORT/MERGE (USING/GIVING, INPUT/OUTPUT PROCEDURE), RELEASE, RETURN | | File I/O | OPEN (INPUT/OUTPUT/EXTEND/I-O), CLOSE, READ (INTO + AT END/NOT AT END body), WRITE (FROM + AFTER/BEFORE ADVANCING), REWRITE, DELETE, START (KEY IS) | | FILE STATUS | Tracked on FileAdapter ("00"/"10"/"35"/"30"), auto-updated after every I/O operation | | Report Writer | RD, TYPE IS, LINE/COLUMN, SOURCE, SUM, GROUP INDICATE, INITIATE, GENERATE, TERMINATE | | Screen Section | LINE, COL, PIC, VALUE, USING, FROM, TO, BLANK SCREEN, display attributes, ACCEPT/DISPLAY with screen names | | Intrinsics | 41 FUNCTION intrinsics: LENGTH, NUMVAL, UPPER-CASE, LOWER-CASE, REVERSE, TRIM, MAX, MIN, MOD, ABS, SQRT, LOG, SIN, COS, CURRENT-DATE, RANDOM, MEAN, MEDIAN, FACTORIAL, SIGN, INTEGER-OF-DATE, DATE-OF-INTEGER, CONCATENATE, TEST-NUMVAL, PI, E, and more | | Preprocessing | COPY resolution with recursive expansion, REPLACING (pseudo-text + LEADING/TRAILING + non-pseudo-text), cycle detection, case-insensitive copybook lookup | | EXEC SQL | DB-API 2.0 code generation: DECLARE/OPEN/FETCH/CLOSE cursors, SELECT INTO, INSERT/UPDATE/DELETE, COMMIT/ROLLBACK, SQLCA/SQLCODE, host variable parameterization | | EXEC CICS | Enhanced hints: MAP, TRANSID, COMMAREA, RESP/RESP2 extraction | | Declaratives | USE AFTER ERROR/EXCEPTION, USE BEFORE REPORTING, USE FOR DEBUGGING — parsed and translated as handler methods | | Nested programs | Multiple PROGRAM-ID per source, separate Python classes, GLOBAL data hints | | Other | SET (88-level, UP/DOWN BY), CANCEL, INITIALIZE (with REPLACING), ADD/SUBTRACT CORRESPONDING, JSON/XML GENERATE stubs, communication verbs, ENTRY, MicroFocus directives | | Literals | Hex (X"FF"), binary (B"01"), figurative constants (ZERO/SPACE/HIGH-VALUE/LOW-VALUE), EBCDIC collation |

Runtime adapters (included, zero deps)

| Adapter | Purpose | |---------|---------| | CobolDecimal | Fixed-point arithmetic with truncation, ROUNDED mode, signed/unsigned, overflow handling | | CobolString | Fixed-length strings with right-padding, truncation, EBCDIC collation | | FileAdapter | File I/O with OPEN modes, FILE STATUS codes, EOF tracking | | GroupView | Concatenated view of group item fields for group-level MOVE semantics |

Validation

# Interactive test — translate, validate, and execute
cobol2py test program.cob

# Output:
# Testing: program.cob
#   Parse:      OK  (PROG-ID, 15 paragraphs, 0.12s)
#   Analyze:    OK  (3 sensitivities, 2 dependencies)
#   Generate:   OK  (245 lines)
#   Syntax:     OK  (ast.parse passed)
#   Validate:   OK  (import + instantiate passed)
#   Execute:    OK  (exit 0, 0.03s)
#   Output:     "HELLO WORLD"
#   Result: 6/6 checks passed

Corpus validation across 32 test projects including NIST CCVS85 conformance suite (459 files), IBM CICS banking, enterprise DB2, French government tax code, GnuCOBOL test suite, AS/400 ILE, COBOL-in-24-Hours (118 files), and a Minecraft server written in COBOL:

| Check | Result | What it means | |-------|--------|---------------| | Syntax validity | 5,288/5,288 (100%) | Every file produces Python that ast.parse accepts | | Full validation | 5,288/5,288 (100%) | Import + instantiate the generated class |

Performance

Translation is CPU-bound and runs entirely offline — no network, no API calls, no external services. Actual throughput depends on your hardware and the size/complexity of the COBOL source:

| Corpus size | Typical time | Notes | |------------|-------------|-------| | Single file | < 1 second | Instant for most programs | | 100 files | 10–30 seconds | Small project | | 1,000 files | 1–5 minutes | Medium enterprise project | | 5,288 files (full corpus) | 5–10 minutes | Depends on disk I/O and CPU |

Large enterprise migrations with thousands of programs and deeply nested copybook chains will take proportionally longer. The translator processes files sequentially — for maximum throughput on large projects, consider splitting into batches or running on faster hardware.

Test suite

pytest tests/ -v
# 1,031 tests covering parser, analyzer, mapper, conditions, blocks, SEARCH,
# SORT/MERGE, FUNCTION intrinsics, REPORT WRITER, SCREEN SECTION, COPY expansion,
# nested programs, group MOVE, SQL translation, adapters, CLI, batch, validation,
# and 60+ behavioral end-to-end tests

Project structure

src/cobol_safe_translator/
  models.py                — Shared dataclasses (AST, SqlBlock, UseDeclaration, ScreenField)
  parser.py                — COBOL parser (free/fixed format, nested programs, screen section)
  pic_parser.py            — PIC clause parsing and classification
  procedure_parser.py      — PROCEDURE DIVISION + DECLARATIVES splitting
  preprocessor.py          — COPY resolution (recursive), EXEC block extraction
  line_preprocessor.py     — Fixed/free format line continuation handling
  analyzer.py              — Sensitivity detection, dependency extraction, statistics
  mapper.py                — Python code generator (core orchestration)
  mapper_codegen.py        — Code generation mixin (data class, program class, header)
  mapper_verbs.py          — Verb translation mixin (MOVE, GO TO, PERFORM, arithmetic)
  condition_translator.py  — Recursive descent COBOL condition → Python expression
  block_translator.py      — IF/EVALUATE/SEARCH block reconstruction
  evaluate_translator.py   — EVALUATE TRUE/variable/ALSO with WHEN THRU ranges
  statement_translators.py — PERFORM, MOVE, miscellaneous verb dispatch
  arithmetic_translators.py — ADD, SUBTRACT, MULTIPLY, DIVIDE, COMPUTE
  function_translators.py  — 41 FUNCTION intrinsic mappings
  string_translators.py    — STRING, UNSTRING, INSPECT, SET
  file_translators.py      — OPEN, CLOSE, READ, WRITE, REWRITE, DELETE, START, CALL
  io_translators.py        — ACCEPT, DISPLAY, REWRITE
  sort_translators.py      — SORT, MERGE, RELEASE, RETURN
  report_parser.py         — REPORT SECTION parser
  report_translators.py    — INITIATE, GENERATE, TERMINATE
  screen_parser.py         — SCREEN SECTION parser
  screen_codegen.py        — Screen code generation (ANSI cursor positioning)
  sql_translator.py        — EXEC SQL → DB-API 2.0 Python code generator
  cics_translator.py       — EXEC CICS → Flask/hint translation
  dli_translator.py        — EXEC DLI (IMS database) translation
  exec_block_handler.py    — EXEC block extraction (SQL/CICS/DLI)
  cfg.py                   — Control flow graph (unreachable detection, ALTER)
  adapters.py              — CobolDecimal, CobolString, FileAdapter, GroupView, RedefinesAlias
  indexed_file_adapter.py  — Indexed (VSAM-style) file I/O runtime
  incremental.py           — AST-based + regex-fallback incremental translation
  validation.py            — Runtime import validation (syntax, import, instantiate)
  ebcdic.py                — EBCDIC collation (cp037)
  utils.py                 — Shared utilities (_to_python_name, numeric parsing, shared constants)
  exporters.py             — Markdown and JSON report exporters
  prompt_generator.py      — LLM translation brief generator
  project_analyzer.py      — Multi-file project analysis an