infochanged

Workers - Workers tracing — write custom spans with new startActiveSpan() and span.end() runtime APIs

Announced: 2026-07-28
Tags: Workers
Severity: info, set by reef/rss-rule-v1
Source: https://developers.cloudflare.com/changelog/post/2026-07-28-start-active-span/

The Workers runtime now provides built-in <code>tracing.startActiveSpan()</code> and <code>span.end()</code> APIs, allowing you to write custom spans for operations that last beyond a single callback — for example, instrumenting a stream pipeline where the span should stay open until the stream is fully consumed. This augments the <a href="https://developers.cloudflare.com/changelog/post/2026-06-16-custom-spans/">existing API for writing custom spans</a>, <code>tracing.enterSpan()</code>, which automatically ends a span when its callback is returned. With <code>startActiveSpan()</code>, the span remains open after the callback returns, and you call <code>span.end()</code> when the work is complete: <div><div data-nb-tabs data-nb-sync-key="workersExamples" class><div class="relative flex border-b border-border" role="tablist" data-nb-tabs-list></div><div class="mt-3"><div role="tabpanel" data-nb-tabs-content data-nb-tab-label="JavaScript" class><figure class="nb-code-figure nb-code-figure-titled" data-nb-lang="js"><figcaption class="nb-code-title">src/index.jsjs</figcaption><pre class="astro-code astro-code-themes github-light github-dark nb-shiki-c6xiwz" tabindex="0" data-language="js" data-nb-lang="js"><code>import { tracing } from "cloudflare:workers"; const encoder = new TextEncoder(); export default { fetch() { return tracing.startActiveSpan("stream-response", (span) => { let timer; const body = new ReadableStream({ start(controller) { controller.enqueue(encoder.encode("Starting...\n")); timer = setTimeout(() => { controller.enqueue(encoder.encode("Complete.\n")); controller.close(); span.setAttribute("stream.status", "complete"); span.end(); }, 1000); }, cancel() { if (timer !== undefined) clearTimeout(timer); span.setAttribute("stream.status", "cancelled"); span.end(); }, }); return new Response(body, { headers: { "content-type": "text/plain" }, }); }); }, };</code></pre></figure></div><div role="tabpanel" data-nb-tabs-content data-nb-tab-label="TypeScript" class><figure class="nb-code-figure nb-code-figure-titled" data-nb-lang="ts"><figcaption class="nb-code-title">src/index.tsts</figcaption><pre class="astro-code astro-code-themes github-light github-dark nb-shiki-c6xiwz" tabindex="0" data-language="ts" data-nb-lang="ts"><code>import { tracing } from "cloudflare:workers"; const encoder = new TextEncoder(); export default { fetch(): Response { return tracing.startActiveSpan("stream-response", (span) => { let timer: ReturnType<typeof setTimeout> | undefined; const body = new ReadableStream<Uint8Array>({ start(controller) { controller.enqueue(encoder.encode("Starting...\n")); timer = setTimeout(() => { controller.enqueue(encoder.encode("Complete.\n")); controller.close(); span.setAttribute("stream.status", "complete"); span.end(); }, 1000); }, cancel() { if (timer !== undefined) clearTimeout(timer); span.setAttribute("stream.status", "cancelled"); span.end(); }, }); return new Response(body, { headers: { "content-type": "text/plain" }, }); }); }, };</code></pre></figure></div></div></div><script type="module" src="https://developers.cloudflare.com/home/runner/work/cloudflare-docs/cloudflare-docs/src/components/ui/tabs/Tabs.astro?astro&type=script&index=0&lang.ts"></script></div> For more details, refer to the <a href="https://developers.cloudflare.com/workers/observability/traces/custom-spans/">custom spans documentation</a>.

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