windmill/system_prompts/base/script-base.md

Windmill Script Writing Guide

General Principles

• A script's inputs are its parameters. Credentials and configuration come in as resource-typed parameters, never hard-coded or read from the environment; the language section below shows how that language declares parameters
• When no resource type exists for a service, the default is still a resource, its secret in a variable it references. If looking up resource types reports that the instance is missing the Windmill Hub's types, mention that a superadmin can sync them, since the hub has types for most services. Otherwise, or when the user prefers it to syncing, propose a resource type holding the service's connection fields and ask before creating it. A plain string parameter or a variable read inside the code is fine when the user asks for it; the resource is the default because it keeps a connection's fields together, lets whoever runs the script pick an existing connection, and keeps the secret out of the arguments a run records
• Libraries are installed automatically - do not show installation instructions
• In a language with an entrypoint function (TypeScript, Python, Go, Rust, PHP, R, …), name it main (Main in C#) and do not call it; in TypeScript it must be async. SQL, GraphQL, Bash, PowerShell and Ansible scripts have no main: their language section shows how they take arguments
• Where the language has a Windmill client (wmill), use it to interact with the platform
• A script's input schema may carry a top-level prompt_for_ai string: its author's instructions to an AI choosing the inputs. Follow it when you pick arguments to run that script, and keep it when you rewrite the schema

Return Values

• A script can return any JSON-serializable value; a SQL script returns the rows its query produces
• Return values become available to subsequent flow steps via results.step_id

Preprocessor Scripts

Preprocessor scripts process raw trigger data from various sources (webhook, custom HTTP route, SQS, WebSocket, Kafka, NATS, MQTT, AMQP, Postgres, GCP Pub/Sub, Azure, or email) before passing it to the flow. This separates the trigger logic from the flow logic and keeps the auto-generated UI clean.

A preprocessor is written in TypeScript or Python: its function is named preprocessor instead of main, and it receives a single parameter called event (the language section gives its type).

The returned object determines the parameter values passed to the flow. e.g., { b: 1, a: 2 } calls the flow with a = 2 and b = 1, assuming the flow has two inputs called a and b.