legacy2mcp

Turn a legacy SOAP/WSDL system into a safe, typed MCP server in minutes — so an AI agent can call it without a hand-written adapter.

Point legacy2mcp at a WSDL URL. It introspects every operation, generates a real JSON Schema for each one from the WSDL's own XSD types, and exposes them as MCP tools that any MCP client (Claude Desktop, an agent framework, your own code) can call — with every call schema-validated before it reaches your SOAP endpoint, write-like operations excluded by default, and every call audit-logged.

No hand-written adapter code. No hand-maintained tool schemas that drift from the WSDL. No arbitrary calls the WSDL itself doesn't define.

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Why this exists

Organizations run 10–20 year old SOAP services that aren't going away — systems of record, middleware, back-office and line-of-business platforms. More and more teams now want to point an AI agent at these systems.

Today that means, per WSDL:

• hand-writing a bespoke adapter,
• guessing at input validation,
• hand-copying tool schemas that immediately start drifting from the service,
• and hoping nobody points an LLM at DeleteRecord.

legacy2mcp generates the adapter from the WSDL itself, so the tool schema can never drift from what the service actually accepts, and ships a safe-by-default posture (no writes without an explicit opt-in, no unvalidated arguments, every call logged) instead of leaving that to whoever wrote the last adapter.

Features

• Zero adapter code — one MCP tool per WSDL operation, named <adapter_id>_<Operation>.
• Real schemas from the WSDL's XSD — simple types, nested complex types, enums, and repeated elements (arrays) are all handled recursively, depth-limited for pathological WSDLs.
• Safety net #1: validation — every call runs through jsonschema.validate (with additionalProperties: false) before any network call.
• Safety net #2: read-only by default — operations whose names look like writes (Create*, Update*, Delete*, Cancel*, Submit*, Pay*, …) are not exposed unless you set allow_write_operations: true.
• Explicit allow/deny lists — include_operations / exclude_operations on top of the heuristic.
• Audit log — one JSON line per call: tool, arguments, timestamp, outcome.
• Secrets stay out of config — passwords are read from named environment variables, never written into the YAML.
• CI-friendly dry run — legacy2mcp inspect lists the generated tools and exits, so a broken WSDL fails your pipeline instead of your production agent.

See docs/security.md for the full, honest security model — what's covered today and what isn't yet.

Install

pip install legacy2mcp          # or: uv tool install legacy2mcp / pipx install legacy2mcp

Also on the MCP Registry as io.github.bvenkata/legacy2mcp, so MCP-aware clients that read the registry can discover it directly.

Quick start

git clone https://github.com/bvenkata/legacy2mcp.git
cd legacy2mcp
pip install -e ".[dev]"

# 1. Start the bundled demo SOAP service (no external network needed)
python examples/soap/run_mock_calculator.py &

# 2. See the MCP tools generated from its WSDL
legacy2mcp inspect --config examples/soap/config.calculator.yaml

Or with Docker:

docker compose up demo-soap-service -d
docker compose run --rm legacy2mcp legacy2mcp inspect \
  --config examples/soap/config.calculator.docker.yaml

Point it at your own WSDL

# config.yaml
server:
  name: my-legacy-mcp

adapters:
  - id: legacy
    type: soap
    config:
      wsdl_url: "https://service.example.com/LegacyService?wsdl"
      auth:
        type: basic
        username: "svc-account"
        password_env: "SERVICE_PASSWORD"
      # Safe by default: Create*/Update*/Delete*/Cancel*/Submit*/... are
      # excluded unless you opt in explicitly.
      allow_write_operations: false
      # Recommended for production: enumerate exactly what the agent may call.
      include_operations: ["GetRecord", "GetRecordDetails", "SearchRecords"]

security:
  audit:
    enabled: true
    path: "./legacy-mcp-audit.log"

export SERVICE_PASSWORD=...
legacy2mcp inspect --config config.yaml   # review the generated tools
legacy2mcp run     --config config.yaml   # start the MCP server (stdio)

A full production-shaped template lives at examples/soap/config.template.yaml.

Use it from Claude Desktop (or any MCP client)

{
  "mcpServers": {
    "legacy": {
      "command": "legacy2mcp",
      "args": ["run", "--config", "/absolute/path/to/config.yaml"]
    }
  }
}

Use cases

• Systems of record — let an agent read status and detail records from a legacy back-office platform, read-only, with every lookup audit-logged.
• Financial services — expose account and transaction reads to an agent without exposing transfers or adjustments.
• Supply chain / ERP — surface order status, inventory, and shipment tracking from an old SOAP middleware layer.
• Internal support tooling — give a support copilot safe, typed access to the system of record instead of a scraped UI.
• Migration & modernization — put an MCP layer in front of a legacy service now, and swap the backend later without touching the agent.

Real-world usage

In CI/CD — catch WSDL drift before it reaches production

legacy2mcp inspect loads the config, contacts the WSDL, builds every tool schema, and exits non-zero if anything fails. Run it as a pipeline gate:

# .github/workflows/contract-check.yml
- name: Check the WSDL still generates valid MCP tools
  env:
    SERVICE_PASSWORD: ${{ secrets.SERVICE_PASSWORD }}
  run: |
    pip install legacy2mcp
    legacy2mcp inspect --config config/legacy.yaml > tools.json
    # optionally: diff tools.json against a committed snapshot to catch
    # a backend team changing an operation's contract out from under you
    git diff --exit-code --no-index tools/legacy.snapshot.json tools.json

As a sidecar / long-running MCP server

legacy2mcp run speaks MCP over stdio — the transport Claude Desktop and most agent frameworks spawn servers over. Package it with your config in the provided Dockerfile and let your MCP client launch it.

In a data pipeline

Use the same generated, validated tools from your own Python (via any MCP client library) to pull records from the legacy system on a schedule, with the audit log giving you a record of exactly what was fetched.

What it actually does, precisely

1. Loads the WSDL with zeep, a mature, widely used Python SOAP client.
2. For every operation on every port/binding, converts the WSDL's XSD input type into a JSON Schema (src/legacy2mcp/schema/xsd_to_jsonschema.py) — simple types, nested complex types, enums, and arrays, recursively.
3. Registers one MCP tool per operation, named <adapter_id>_<OperationName>.
4. On a tool call: validates arguments against that operation's JSON Schema, calls the SOAP operation via zeep, serializes the response back to plain JSON, and writes an audit log entry.
5. Operations whose names look like writes are excluded unless allow_write_operations: true — see docs/security.md for exactly what this heuristic does and doesn't catch.

Status

v0.1 — the SOAP/WSDL adapter is implemented and tested (pytest tests/ runs against an in-process mock SOAP service, no network needed). A database adapter (safe, parameterized-query-only, table/operation allowlists) and a queue adapter (Kafka/RabbitMQ/SQS) are on the roadmap but not implemented yet — the BaseAdapter interface (src/legacy2mcp/adapters/base.py) is the extension point if you want to build one.

Development

pip install -e ".[dev]"
pytest tests/ -v

CI runs the suite on Python 3.10–3.12 (.github/workflows/ci.yml). Releases to PyPI and the MCP Registry are tag-triggered — see docs/releasing.md.

Contributing

Adapters for new legacy systems are the highest-value contribution — implement BaseAdapter (discover_tools() + invoke()) and the MCP server core handles validation, dispatch, and audit logging for you automatically. Issues and PRs welcome.

License

Apache 2.0 — see LICENSE.