Marketplace price comparison

What to build

Item search → seller offers and buy-order tables → a daily chart for a selected marketplace. Your server stores the key and caches public market data. The browser receives only the required fields.

Request sequence

1. Debounced GET /v1/items?q=…&limit=20, not one request for every keystroke.
2. GET /v1/items/{item_id}/markets for the selected item.
3. GET /v1/items/{item_id}/history for one marketplace and a bounded date range.

Sort asks by ascending amount and bids by descending amount. Keep them separate. Format money using minor_units. Do not equate Steam wallet balances with withdrawable cash balances.

Acceptance checks

• Search displays API results, not hard-coded demonstration prices.
• Selecting another phase uses that phase’s item_id.
• Empty history has a clear empty state.
• Charts do not contain points absent from the response.
• 429 respects Retry-After; 401 stops further requests.
• Keys do not appear in HTML, browser bundles, URLs or logs.
• Repeated views use a shared cache; 100 viewers do not cause 100 upstream requests.

This compares observed offers. It is not a trading bot or a promise of profit.

Runnable starter

Get Market comparison starter and the SDK from Downloads. Their exact filenames and SHA-256 values are in the manifest (examples and artifacts). Verify checksums, extract the starter into a new directory, install the local SDK archive with npm install --ignore-scripts /path/to/archive.tgz, set CSFOLDER_API_KEY in the server environment, then run npm start. Open http://127.0.0.1:4319. Node.js 22+ is required; follow the bundled README.

This English reference UI uses real API responses, not bundled demo prices. It shows the last 30 UTC days of daily asks as individual dots with a data table. Search pagination, bid-only items, unknown timestamps and empty history are explicit. Quotes/history cache for 30 minutes; search caches for 30 seconds. 401/403 and exhausted monthly quota require an operator fix and server restart; 429 pauses requests until Retry-After, with explicit retry. No background polling.

The app is local-only, not a publicly deployable unauthenticated proxy. Before hosting it for users, add app authentication, per-user abuse controls and shared caching/limits across replicas. Do not expose it through a tunnel as-is. The starter does not provision API access; check release availability first.