DIAL OpenAPI to MCP

DIAL OpenAPI to MCP is a bridge that turns a REST API into MCP tools, one tool per operation in the API's OpenAPI 3.x document. It runs as an application type: each application of the type holds one API's document and address, and DIAL Core sends them to the bridge with every MCP request. This reference is for platform engineers who deploy the bridge next to DIAL Core. For the screens where the type and its applications are created, see Application runners.

info

• Repository
• Releases
• Docker Hub image tags

How it works

The client is usually a Quick App. The bridge asks DIAL Core for a credential only when the application names an external service.

1. Core loads the schema. The type's registration points dial:applicationTypeSchemaEndpoint at the bridge's /v1/configuration-support/application-schema. The schema declares the four application properties.
2. A client calls an application over MCP. Core serves POST /v1/deployments/<application>/mcp and forwards the message to the bridge's /mcp. It adds the application's properties to params._meta.ai_dial_config, the application ID in X-DIAL-APPLICATION-ID, and a per-request key in API-KEY.
3. The bridge builds the tools. It reads the document and the base URL, creates the tools with FastMCP, and caches them per document and base URL.
4. A tool call becomes an HTTP request. The bridge calls the operation with the tool's arguments and returns the response as the tool result. When the application sets external_service, the bridge first gets the caller's credential from Core and adds it as a header.

Core reports features.mcp for applications of the type, so a Quick App's dial-app Toolset calls them over MCP. To set up an application, see Expose a REST API as MCP tools.

Tools

• One tool per operation. A tool is named after its operation's operationId. In the upstream example, the operation listTodos becomes the tool listTodos.
• OpenAPI 3.x only. The bridge rejects a Swagger 2.0 document, and any openapi version other than 3.x.
• x-mcp overrides. On an operation, x-mcp.name renames the tool, which needs an operationId. x-mcp.description replaces the tool's description, and x-mcp.parameters.<name>.description replaces a parameter's description. Release 0.2.1 reads no other x-mcp keys, so the inputSchema, outputSchema, and tags in the upstream *-extended.json samples have no effect.
• Utility tools. When a request carries no document, or a null or empty one, the bridge offers two tools of its own:
  • openapi_verify(spec) checks that a document parses, is OpenAPI 3.x, has info.title, info.version, and paths, and that FastMCP can build tools from it. When FastMCP fails, it checks each path of a document with up to 50 paths and reports which ones fail.
  • openapi_convert(spec) converts a Swagger 2.0 document to OpenAPI 3.0, and returns an OpenAPI 3.x document unchanged.

Dependencies

Dependency	Purpose
DIAL Core	Registers the application type, sends MCP requests to the bridge, and stores external-service credentials. DIAL 1.47, the first platform release with the bridge, pairs it with DIAL Core 0.47.0.
REST APIs	The destinations of tool calls. The bridge needs network access to each API's base URL.
OpenTelemetry collector or Prometheus, optional	Receives traces, metrics, and logs when an exporter is set. See Observability.

Deployment

Item	Value
Image	ghcr.io/epam/ai-dial-openapi-to-mcp:0.2.1, Python 3.13 on Alpine, running as the non-root user appuser (UID 1001)
MCP endpoint	Streamable HTTP at /mcp, port 8080 (MCP_PORT)
Schema endpoint	GET /v1/configuration-support/application-schema
Liveness	GET /health returns 200 and {"status": "ok"}
Readiness	GET /ready returns 200 and {"status": "ready"} after startup, and 503 before
Metrics	Port 9464, when OTEL_METRICS_EXPORTER includes prometheus
Helm	Not part of the dial chart. Deploy it with the dial-extension chart; see the example.

The DIAL 1.47 and 1.48 platform releases pin 0.2.1.

Warning

The bridge doesn't authenticate its clients and calls any destination a request names. In 0.2.1, it also passes the per-request key that DIAL Core sends on to the API. Read Secure the bridge before you expose it.