observability

Effect Logging

import { Effect } from "effect";

const program = Effect.gen(function* () {
  yield* Effect.log("Starting process");
  yield* Effect.logDebug("Debug info", { userId: "123" });

  const result = yield* doWork();

  yield* Effect.logInfo("Process complete", { result });
  return result;
}).pipe(
  Effect.withSpan("processOrder", { attributes: { orderId } })
);

Structured Spans

import { Effect } from "effect";

const processOrder = (orderId: string) =>
  Effect.gen(function* () {
    yield* validateOrder(orderId).pipe(Effect.withSpan("validate"));
    yield* chargePayment(orderId).pipe(Effect.withSpan("charge"));
    yield* sendConfirmation(orderId).pipe(Effect.withSpan("notify"));
  }).pipe(Effect.withSpan("processOrder"));

Spans are automatically nested and exported to OTEL collectors.

OTEL Integration

import { NodeSdk } from "@effect/opentelemetry";
import { OTLPTraceExporter } from "@opentelemetry/exporter-trace-otlp-proto";

const OtelLive = NodeSdk.layer(() => ({
  resource: { serviceName: "my-service" },
  spanProcessor: new BatchSpanProcessor(new OTLPTraceExporter()),
}));

// Provide to your program
const main = program.pipe(Effect.provide(OtelLive));

Anti-Patterns

• console.log → Use Effect.log (structured, traced)
• console.error → Use Effect.logError (with stack traces)
• Custom logger → Use Effect's built-in (integrates with OTEL)