marketplace price plugin (eBay + Amazon)

Price research for protoAgent — what an item actually sold for, and what you'd keep after fees.

ebay_price_and_profit("nintendo switch oled", item_cost=120, shipping_cost=12)

  stats        median $200.75   p25–p75 $170.49–$225.99   (60 sold comps)
  breakeven    $155.32
  at median    sale $200.75 → fees $27.70 → net $41.05 (20.4%)

Why a browser and not the eBay API

The number a seller prices against is sold comps. That data lives behind eBay's Marketplace Insights API, which eBay lists as Limited Release and closed to new applicants — while the same data is plainly visible in the normal web UI to a signed-in user. So this drives a real signed-in browser (the agent-browser CLI) instead of an API.

No developer keys, no OAuth, and the plugin never handles your credentials — you sign in by hand, once, in a browser window.

What that costs, stated plainly:

Sign-in required	eBay serves the sold view only to signed-in users.
Headed only	eBay answers headless browsers with an error page.
Rate-limited	Hit either site hard and you get verification pages. min_interval_s paces requests; raise it if that happens.
Markup isn't a contract	Selectors were verified live and will eventually break. The tools distinguish "no results" from "couldn't read the page" and report the second as a bug.
Thin searches are padded	A search with few exact matches gets a "Results matching fewer words" river of loosely related items. The tools count only the exact matches and report the rest as related_rows_excluded, with eBay's own headline_count alongside.

This plugin makes no attempt to defeat bot detection — no proxy rotation, no fingerprint spoofing, no CAPTCHA solving. It drives a normal browser at a human pace. When eBay asks for verification, the tools say so and hand it to you.

Setup

npm i -g agent-browser && agent-browser install       # the browser CLI
protoagent plugin install https://github.com/protoLabsAI/ebay-plugin

# langgraph-config.yaml
plugins:
  enabled: [ebay]
ebay:
  profile: ~/.protoagent/ebay-profile   # REQUIRED — this is what keeps you signed in
  headed: true
  stealth: false                        # true if your eBay account signs in through Google (below)
  domain: www.ebay.com                  # www.ebay.co.uk, www.ebay.de, …
  amazon_domain: www.amazon.com

Then ask the agent to run ebay_session_status, and sign in once in the window that opens. The profile persists it.

Signing in through Google

Chrome sets navigator.webdriver when it is driven over CDP, and Google refuses to sign an account in from such a browser ("This browser or app may not be secure"). If your eBay account signs in through Google, set stealth: true: the browser launches with --disable-blink-features=AutomationControlled — the same flag protoAgent's core browser plugin uses for its stealth option — and nothing else changes. The browser still identifies as Chrome and runs at a human pace; this is not an attempt to defeat eBay's own checks. An eBay password or passkey login needs none of this.

profile, headed and stealth are daemon-level launch options in agent-browser. The plugin sends them with every page open and the daemon reconciles them against the running browser: unchanged → reused; changed → Chrome relaunches with the new options on the same profile (a sign-in survives); daemon gone → one is respawned with them. So a fresh agent process, a subagent with its own tool set, or a config change all converge on the right browser with nothing to close by hand. (Through 0.2.0 the launch step was a URL-less open, which the CLI turns into a second, option-less launch — every window it opened was replaced within seconds by one on a throwaway profile. Fixed in 0.3.0.) If you ever do need to reset the browser: agent-browser close --session ebay, never close --all, which also kills every other plugin's browser. Two instances that need different profiles need different session names too — one session reconciles to whichever instance opened it last.

Tools

tool	what it's for
ebay_price_and_profit	The one-call answer to "what should I list this at?" — sold comps run through fees and your costs.
ebay_price_check	Median/quartile stats for an item. Sold by default; sold=False for asking prices.
ebay_net_proceeds	Itemized fees, costs, net and margin for one sale.
ebay_breakeven	The lowest price that doesn't lose money.
ebay_search	Individual listings — competitor titles, what's bundled.
ebay_session_status	Signed in? Run this first when something reports a sign-in wall.
ebay_page_probe	Diagnostic: what the extractor sees on a page. For when markup changes.
amazon_price_check	Amazon asking prices. Sponsored rows are flagged and kept out of the statistics.
compare_prices	eBay sold + eBay active + Amazon active, side by side, each labelled with its basis.
price_history	Where today's price sits against what we've recorded before.

A bundled ebay-pricing skill teaches the agent how to narrow a query until the comps are actually comparable, and how to report a price with its basis.

Amazon is not a comp source. It publishes asking prices only — the Buy Box, one offer among several. eBay's sold view is the only real sale data here, and every result is labelled so the two can never be reported as the same kind of number.

Fees

Fee rates are config, not knowledge. Schedules change and vary by category, store subscription and country, so the shipped defaults carry their own provenance and every result says whether they've been verified:

ebay:
  fees:
    final_value_pct: 13.6      # most US categories, no store
    per_order_fee: 0.40        # 0.30 at/under $10
    international_pct: 1.65
    promoted_pct: 0.0          # only if the sale came via a Promoted Listing
    verified_on: "2026-08-05"  # set this once you've checked a real invoice

Until verified_on is set, every result carries an UNVERIFIED caveat. Two subtleties the calculator gets right and most don't:

• Sales tax inflates the fee base. eBay computes its cut on a total that includes tax you never receive.
• Free shipping isn't free. It moves the cost to you while eBay still charges on what the buyer paid.

Payment processing defaults to zero — eBay's managed payments bundles it into the final value fee, so charging it again would double-count. A PAYPAL_GOODS_SERVICES schedule is provided for sales taken outside eBay.

What this does NOT do

• No Amazon SOLD data. Amazon publishes asking prices only — nothing there says what buyers actually paid. eBay's sold comps are the only real sale data in this plugin, and the tools label which is which so the two can't be confused. (Amazon's Product Advertising API is deprecated and returns 403; its replacement needs an Associates account with qualifying referred sales, so the browser is the only route.)
• No retrospective price history. price_history reads a log this plugin writes itself, so it starts empty and accumulates from the day you enable it. Gaps mean nobody searched, not that the price held steady. Reconstructing history before that needs a paid third party (Keepa and similar).
• No listing management. Nothing here publishes a listing, changes a live price, contacts a buyer or touches an order. Seller-side automation is deliberately deferred until the Seller Hub markup can be verified against a signed-in session — guessing at it is precisely the mistake that produced three defects during this plugin's own development.
• No sell-through rate. Sold comps show what sold, never how many didn't.

Development

pip install -r requirements-dev.txt
pytest -q          # 114 tests, no protoAgent host and no browser required
ruff check . && ruff format --check .

The money-handling fixtures are real strings captured from a live eBay results page, not imagined ones. That matters: the first draft used .s-item__shipping from memory, which matches nothing on eBay's current s-card layout — it would have silently reported every listing as free-shipping and ranked a $10-plus-$15 item above a $20-shipped one.