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Schema and TaggedError are re-exported from Sideffect for convenience so users do not need to install or import from the effect package directly. Every schema you need to describe workflow payloads, step inputs, and step outputs is available through this single import. 
import { Schema, TaggedError } from "sideffect";

​
Schema

Schema is the full Schema namespace re-exported from the effect library. You use it to describe the shape of workflow payloads and step inputs and outputs. Sideffect passes every payload and result through Schema.decodeUnknownSync at runtime, so schemas must be decodable from unknown values (as all built-in schemas are).

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Primitive schemas

SchemaTypeScript typeNotes
Schema.Stringstring
Schema.Numbernumber
Schema.Booleanboolean
Schema.VoidvoidUseful for steps that return nothing
Schema.Uint8ArrayUint8ArrayFor binary payloads such as image data

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Composite schemas

Schema.Struct({ ... }) — Describes a plain object with named fields: 
const ImagePayload = Schema.Struct({
  imageKey: Schema.String,
  width: Schema.Number,
  lossless: Schema.Boolean,
});
// TypeScript type: { readonly imageKey: string; readonly width: number; readonly lossless: boolean }
Schema.Array(innerSchema) — Describes an array of values that all conform to innerSchema: 
const Tags = Schema.Array(Schema.String);
// TypeScript type: readonly string[]

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Transformation schemas

Schema.NumberFromString — Decodes a string and parses it into a number. This is particularly useful when your workflow’s event payload arrives from an HTTP request or a queue message where numeric values are serialized as strings: 
import { Schema, Workflow } from "sideffect";

const payloadDecodingWorkflow = Workflow.make({
  name: "payload-decoding",
  payload: Schema.Struct({ value: Schema.NumberFromString }),
});

// The raw Cloudflare event carries { value: "42" } (a string).
// After decoding, workflow.payload.value is the number 42.
export const payloadDecodingLayer = payloadDecodingWorkflow.toLayer(
  async (workflow, step) => {
    console.log(typeof workflow.payload.value); // "number"
    console.log(workflow.event.payload.value);  // "42" (original string, pre-decode)
  },
);

​
TaggedError

TaggedError is re-exported from effect/Data. It is a base class for creating typed, discriminated error classes. Using tagged errors makes it straightforward to handle specific failure cases in Effect-based step implementations.

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Defining a custom tagged error

import { TaggedError } from "sideffect";

class UserNotFoundError extends TaggedError("UserNotFoundError")<{
  readonly userId: string;
}> {}

class QuotaExceededError extends TaggedError("QuotaExceededError")<{
  readonly limit: number;
  readonly current: number;
}> {}

​
Using tagged errors in a step

import { Effect } from "effect";
import { Schema, Step, TaggedError } from "sideffect";

class UserNotFoundError extends TaggedError("UserNotFoundError")<{
  readonly userId: string;
}> {}

const fetchUser = Step.make("fetch user", {
  payload: Schema.Struct({ userId: Schema.String }),
  result: Schema.Struct({ name: Schema.String, email: Schema.String }),
  run: ({ userId }, ctx) =>
    Effect.gen(function* () {
      const user = yield* Effect.tryPromise(() => ctx.env.DB.get(userId));

      if (!user) {
        yield* Effect.fail(new UserNotFoundError({ userId }));
      }

      return user;
    }),
});
Schema is the complete namespace from the effect library — only the most commonly used schemas in Sideffect patterns are listed above. For the full API including transformations, filters, branded types, and more, see the Effect Schema documentation.

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