Windmill YAML Validator

A TypeScript-based YAML validator for Windmill flow, schedule, and trigger files.

Overview

The windmill-yaml-validator provides runtime validation for Windmill YAML files. It is used by editor integrations to show validation errors while editing:

• flow.yaml / flow.yml
• *.schedule.yaml / *.schedule.yml
• *.{http|websocket|kafka|nats|postgres|mqtt|sqs|gcp}_trigger.yaml (or .yml)

Features

• Unified validation API: One validator class for flow/schedule/trigger files
• Schema-based validation: Uses OpenFlow and backend OpenAPI-derived schemas
• Detailed error reporting: Returns comprehensive error information with specific paths to invalid fields

Installation

npm install windmill-yaml-validator

Usage

Basic Validation

import { WindmillYamlValidator } from "windmill-yaml-validator";

const validator = new WindmillYamlValidator();

const flowYaml = `
summary: Test Flow
value:
  modules: []
`;

const flowResult = validator.validate(flowYaml, { type: "flow" });

const scheduleYaml = `
schedule: "0 0 12 * * *"
timezone: "UTC"
enabled: true
script_path: "f/jobs/daily_sync"
is_flow: false
`;

const scheduleResult = validator.validate(scheduleYaml, { type: "schedule" });

const triggerYaml = `
script_path: "f/triggers/http_handler"
is_flow: false
route_path: "api/webhook"
request_type: "sync"
authentication_method: "none"
http_method: "post"
is_static_website: false
workspaced_route: false
wrap_body: false
raw_string: false
`;

const triggerResult = validator.validate(triggerYaml, {
  type: "trigger",
  triggerKind: "http",
});

console.log(flowResult.errors, scheduleResult.errors, triggerResult.errors);

Target Inference by Filename

import {
  WindmillYamlValidator,
  getValidationTargetFromFilename,
} from "windmill-yaml-validator";

const validator = new WindmillYamlValidator();
const target = getValidationTargetFromFilename(
  "f/webhooks/order_created.http_trigger.yaml"
);

if (target) {
  const result = validator.validate(fileContents, target);
  console.log(result.errors);
}

Error Handling

const invalidYaml = `
summary: 123  # Should be a string
value:
  modules:
    - id: step1
      value:
        type: rawscript
        language: invalid_language  # Invalid enum value
`;

const result = validator.validate(invalidYaml, { type: "flow" });

result.errors.forEach((error) => {
  console.log(`Error at ${error.instancePath}: ${error.message}`);
  // Example output:
  // Error at /summary: must be string
  // Error at /value/modules/0/value/language: must be equal to one of the allowed values
});

API

WindmillYamlValidator

Main validator class for Windmill YAML validation.

Constructor

new WindmillYamlValidator();

Initializes AJV validators for flow, schedule, and trigger schemas.

Methods

validate(doc: string, target: ValidationTarget)

Validates a YAML document against the selected target schema.

Parameters:

• doc (string): YAML document string
• target (ValidationTarget):
  • { type: "flow" }
  • { type: "schedule" }
  • { type: "trigger", triggerKind: "http" | "websocket" | "kafka" | "nats" | "postgres" | "mqtt" | "sqs" | "gcp" }

Returns:

{
  parsed: YamlParserResult<unknown>;  // Parsed YAML with source pointers
  errors: ErrorObject[];               // Array of validation errors (empty if valid)
}

Throws:

• Error if doc is not a string

getValidationTargetFromFilename(path: string)

Infers validation target from file naming conventions. Returns null for unsupported files.

Development

Building

npm run build

The build process:

1. Runs gen_openflow_schema.sh to generate:
   • src/gen/openflow.json
   • src/gen/schedule.json
   • src/gen/triggers/*.json
2. Removes discriminator mappings (not supported by AJV)
3. Compiles TypeScript to JavaScript

Testing

npm test

Run tests in watch mode:

npm test:watch

Testing locally with the CLI

The Windmill CLI (cli/) is Deno-based and imports this package via npm:[email protected]. Since Deno's npm: specifier always resolves from the npm registry, local testing requires a compatibility script that makes the TypeScript sources directly importable by Deno.

The deno-compat.sh script handles two Deno requirements:

• Adding .ts extensions to relative imports
• Adding with { type: "json" } assertions to JSON imports

Steps:

1. Apply Deno compatibility:

./deno-compat.sh

2. Add the following entries to cli/deno.json imports:

"npm:[email protected]": "../windmill-yaml-validator/src/index.ts",
"ajv": "npm:ajv@^8.17.1",
"@stoplight/yaml": "npm:@stoplight/yaml@^4.3.0"

3. Run the CLI directly with Deno:

cd ../cli
deno run -A src/main.ts lint

4. When done, restore everything:

./deno-compat.sh -r     # restore original imports
# Remove the 3 import map lines from cli/deno.json

Schema Generation

The validator uses a JSON schema generated from the OpenAPI specification:

./gen_openflow_schema.sh

This script:

• Converts openflow.openapi.yaml and backend/windmill-api/openapi.yaml into JSON
• Removes discriminator mappings for AJV compatibility
• Removes the ToolValue discriminator entirely (see below)
• Generates standalone schedule/trigger schemas for CLI file shape

Why Remove Discriminators?

The OpenFlow schema uses OpenAPI discriminators for efficient type resolution in oneOf schemas. However, AJV's discriminator support has limitations:

1. Discriminator Mappings: Not fully supported by AJV, so they are removed from all schemas
2. ToolValue Discriminator: Completely removed because FlowModuleTool uses allOf composition, which prevents AJV from finding the discriminator property (tool_type) at the expected location

Impact: Without discriminators, AJV falls back to standard oneOf validation, which:

• Tests each alternative until one matches
• Is slightly slower but still performant for our use case
• Provides the same validation correctness
• Works correctly with complex schema compositions like allOf

Breaking Change

FlowValidator and validateFlow() were replaced by WindmillYamlValidator and validate(doc, target).