Price Monitoring

Given a list of products (ASINs, Walmart URLs, or free-text Google Shopping queries) and an optional baseline file, fetch current prices via ScraperAPI's structured endpoints, compare against the baseline, and produce a structured change report.

You — Claude — execute the API calls using the Bash tool. Do not generate a script for the user to run; fetch the data yourself in this turn and report findings as you go. If the user explicitly asks for a CLI/cron-able script instead, point them at scraperapi-cli and stop.

Auth: All transports authenticate against ScraperAPI. The MCP server reads the key from its own configured environment when the user set it up. The curl fallback reads $SCRAPERAPI_API_KEY from the shell. Do not run a standalone check for the key — just make the first real request. ScraperAPI returns 401 if the key is missing or invalid, and Phase 3's failure-handling table already covers that case. Adding a pre-flight echo only costs the user an extra permission prompt without learning anything you wouldn't learn from the first call.

Phase 1 — Parse the watchlist

Before fetching anything, classify each target. Different inputs route to different ScraperAPI endpoints, and routing wrong wastes credits.

Announce the parsed plan before running: "Watchlist parsed: 3 Amazon products, 1 Walmart product, 1 Google Shopping query. Baseline: prices.json (last updated 2026-05-25). Fetching now."

For Amazon URLs, extract the ASIN with a regex like /(?:dp|gp/product)/([A-Z0-9]{10})/ — the structured endpoint is faster and cheaper when given the ASIN directly than when given the full URL.

Phase 2 — Load the baseline (if any)

The baseline is a JSON file the user maintains across runs. Its shape is documented in assets/price-baseline-template.json. If the user references a baseline file, read it before fetching so you can compare in a single pass.

If no baseline exists, treat this run as the first capture — every product becomes a baseline entry, and the change report only lists currently-observed prices (no deltas). Offer to write the file at the end so the next run can compare against it.

Never silently overwrite a baseline without confirming. If the user wants the file updated, do it explicitly at the end of the run after they see the report.

Phase 3 — Fetch current prices

Use the ScraperAPI MCP server for this skill. Tools like amazon_product, walmart_product, and google_shopping give typed arguments and structured responses with no shell-quoting or stdout-parsing concerns, which is what you want for a pricing workflow where field accuracy matters.

If the ScraperAPI MCP server is listed as still connecting, wait briefly and re-check with ToolSearch before doing anything else. If MCP is genuinely unavailable, fall back to curl (documented below) — do not reach for the sapi CLI here, even if it is on $PATH. CLI output requires shell parsing that's error-prone for price data, and this skill stays simpler by routing all price calls through one transport.

At the end of the report, if you had to use the curl fallback, mention that installing the MCP server (scraperapi-mcp skill covers setup) will simplify future runs. Never block the current run on installing tooling.

Run all targets in parallel — multiple tool calls in a single message — so a 10-product watchlist finishes in roughly one round-trip rather than ten.

MCP tools

See the scraperapi-mcp skill for full schemas. Walmart's MCP tool takes a product ID, not a URL — strip the /ip/<id> segment.

curl fallback

curl -sG "https://api.scraperapi.com/structured/amazon/product" \
  --data-urlencode "api_key=$SCRAPERAPI_API_KEY" \
  --data-urlencode "asin=B08N5WRWNW" --data-urlencode "country=us"

curl -sG "https://api.scraperapi.com/structured/walmart/product" \
  --data-urlencode "api_key=$SCRAPERAPI_API_KEY" \
  --data-urlencode "url=https://www.walmart.com/ip/123456789"

curl -sG "https://api.scraperapi.com/structured/google/shopping" \
  --data-urlencode "api_key=$SCRAPERAPI_API_KEY" \
  --data-urlencode "query=airpods pro 2" --data-urlencode "country=us"

Expected response fields (same for MCP and curl)

• Amazon: pricing (formatted string like "$129.99"), list_price, availability_status, product_information.title, offers. Parse the number out of pricing and carry the currency separately.
• Walmart: price, availability, seller_name, product_name.
• Google Shopping: shopping_results[] with title, price, extracted_price (numeric when ScraperAPI can parse it), source (retailer), link.

The exact field names occasionally drift — inspect the first real response of a run and adapt parsing if needed.

Handling failures

MCP tools surface errors as tool-call errors; curl returns an HTTP status code.

Do not retry forever. Failed targets after retries get a status: "failed" row in the report so the user knows what's missing.

Credit budget

Each structured call typically costs ~5 credits. A 50-product watchlist is ~250 credits per run. Before kicking off batches larger than ~100 targets, tell the user the estimate and confirm. If they want recurring monitoring at large scale, recommend they move to a scheduled CLI (scraperapi-cli) or DataPipeline rather than burning credits through this skill on every check.

Phase 4 — Compare and classify

For each target, compute the delta against the baseline. Classify into one of these states — the report becomes much easier to read when changes have consistent labels:

If the user gave an explicit alert threshold (e.g., "tell me if AirPods drop below $200"), check it against the current price and surface threshold_hit items prominently at the top of the report — that is the user's primary question.

Phase 5 — Produce the report

Render results using assets/price-report-template.md as the structure. Group by state with the most interesting changes first: threshold hits → decreases → restocks → out-of-stock → increases → new → unchanged → failures.

For each row, include:

• product identifier (ASIN, URL, or query)
• title (from the response — helps the user recognize the item)
• baseline price → current price (with currency and date)
• delta as both absolute and percent
• direct link to the listing

End with a one-line summary: "6 of 12 products changed price. Biggest drop: AirPods Pro 2 −15% ($249 → $211). 1 went out of stock. 1 failed."

Phase 6 — Offer to update the baseline

After presenting the report, ask whether to update the baseline file with the new prices. If yes, write the new JSON; preserve fields the user added (e.g., notes, alert_below) by merging rather than overwriting. If no, leave the file untouched.

If this was a first-run capture, do write the baseline (after confirming) — otherwise the next invocation will have nothing to compare against and the loop is pointless.

Stop conditions

This skill is single-shot — it runs once, reports, and stops. It does not loop or schedule itself. If the user wants recurring monitoring:

• For ad-hoc re-checks every few hours: have them re-run the prompt.
• For nightly cron: refer them to scraperapi-cli to generate a script.
• For fully managed scheduling and storage: point them at DataPipeline in the ScraperAPI dashboard (https://dashboard.scraperapi.com/).

Never start a background watcher or write code that polls — that is out of scope for this skill and burns the user's credits without their direct consent each run.

Anti-patterns

• Scraping raw HTML when a structured endpoint exists. The Amazon/Walmart/Google structured endpoints exist precisely so you don't have to parse pricing markup. Use them.
• Silent currency assumptions. Always carry the currency code from the response into the report. A "$1,299" reading is wrong if the listing was in CAD.
• Comparing across countries. If baseline country=us and current country=gb, you are comparing different listings — refuse and ask the user which country to use.
• Overwriting the baseline by default. The baseline is the user's record of truth; touch it only on explicit confirmation.

Reference files

• references/structured-endpoints.md — Exact parameter names, country codes, and known response fields for amazon/product, walmart/product, and google/shopping. Read this before constructing the first request of a run.
• assets/price-baseline-template.json — Shape of the baseline file.
• assets/price-report-template.md — Markdown skeleton for the change report.

For deeper questions about endpoint behavior, link the user to the public docs: https://docs.scraperapi.com/.