Smart Placement Probe

Demonstrate Workers Smart Placement by fetching an origin URL and reporting latency alongside the request colo. wrangler.json sets "placement": { "mode": "smart" } so Cloudflare can place the Worker closer to back-end origins based on traffic patterns.

API ReferenceCopy Anchor Link

GET /Copy Anchor Link

Explains Smart Placement and returns app metadata.

GET /probeCopy Anchor Link

Fetch a URL and report status, latency, and colo.

url string (required)

http:// or https:// target.

Example RequestCopy Anchor Link

curl "https://your-worker.workers.dev/probe?url=https://example.com"

Success ResponseCopy Anchor Link

{
  "url": "https://example.com/",
  "status": 200,
  "latencyMs": 42,
  "cf": { "colo": "SJC" },
  "workerPlacement": "Smart Placement may move this Worker closer to back-end origins based on request patterns."
}

cf.colo comes from the incoming request.cf when available (empty object in local dev).

Error CodesCopy Anchor Link

• 400 - Missing or non-http(s) url (INVALID_URL)

Use CasesCopy Anchor Link

• Learn Smart Placement configuration and behavior
• Measure origin latency from the serving colo
• Compare placement effects after repeated traffic to distant origins
• Debug whether a Worker is running near your back-end

LimitationsCopy Anchor Link

• Smart Placement effects are most visible after deploy with repeated traffic
• Single PoP / colo per request - not a multi-region map
• cf.colo may be empty in local wrangler dev
• No control plane API to force a specific colo

DeploymentCopy Anchor Link

curl "https://your-worker.workers.dev/probe?url=https://example.com"

Local DevelopmentCopy Anchor Link

cd apps/experiments/smart-placement-probe
npm install
npm run dev

curl "http://localhost:8787/probe?url=https://example.com"

Cloudflare Features UsedCopy Anchor Link

• Workers - Edge compute runtime
• Smart Placement - Place Workers closer to back-end origins