Nex-ListingAgent-Native Multi-Marketplace Resale Studio
Turn one item intake into fee-adjusted, rule-checked listings across seven resale marketplaces, with a 4-tier pricing engine, Etsy vintage/handmade eligibility guards, and human-mandate autonomy for offers and delisting.
Built with Next.js 15, React 19, TypeScript, Prisma, PostgreSQL, BullMQ, Playwright, Model Context Protocol (MCP), A2A Agent Card, Tailwind CSS, Vitest, Cloudflare Workers.
7 Channels
Channel-tailored titles, tags, and fee-adjusted net payouts across eBay, Etsy, Poshmark, Mercari, Depop, Shopify, and Facebook Marketplace
4 Price Tiers
High Anchor, Target List, Quick Sale, and a signed Mandate Floor that governs automated offer evaluation
14 MCP Tools
Agent-native MCP and A2A discovery endpoints with scope-checked OAuth and immutable mandate audit trails
What it is
Nex-Listing is an agent-native multi-marketplace resale platform built as a 13-package TypeScript monorepo (Next.js 15 web studio, BullMQ worker, Playwright browser runtime, and an MCP + A2A agent runner). Instead of copying the same title and price across every site, a seller drops one item into the Multi-Marketplace Variant & Mandate Studio and gets channel-tailored copy, category taxonomy, shipping profiles, and fee-adjusted net payouts across eBay, Etsy, Poshmark, Mercari, Depop, Shopify, and Facebook Marketplace (plus local pickup packs for OfferUp and Craigslist). Every automated action—from countering an offer within the seller's floor to cross-marketplace sold-item delisting—is governed by a revocable human Mandate with an immutable audit log.
The problem
Cross-listing tools usually act as dumb form-fillers: they paste identical copy everywhere, ignore platform-specific fee structures that eat margin, and risk account bans by violating marketplace terms (such as listing a modern mass-produced item on Etsy or running unpaced browser scrapes).
What I built
I built a channel-aware variant compiler and 4-tier pricing engine (High Anchor, Target List, Quick Sale, and Mandate Floor) that calculates exact marketplace fees and net payouts per channel before publishing. Channel eligibility guards block non-compliant listings up front—for example, enforcing Etsy's 20-year vintage or handmade rule—while official OAuth API adapters handle eBay, Etsy, and Shopify and human-in-the-loop assisted browser sessions handle Poshmark, Mercari, Depop, and Facebook Marketplace. An agent-native surface exposes 14 MCP tools and a discovery card at /.well-known/agent-card.json so external AI agents can evaluate buyer offers against the seller's signed Mandate floor.
What happened
Live at nex-listing.nexai-rushes.workers.dev with the interactive Multi-Marketplace Variant & Mandate Studio (/studio), Marketplace API Compliance documentation (/compliance), and discovery endpoints, backed by 65 unit, contract, integration, security, and runtime test suites plus 14 Playwright end-to-end tests.
What it changed
- Replaces manual tab-by-tab cross-listing with one intake that respects each marketplace's buyer culture and fee math
- Protects seller accounts by using official OAuth APIs where available and explicit human-confirmed browser sessions everywhere else
- Lets sellers delegate routine offer negotiation to an AI agent without ever dropping below their signed net-payout floor
Who it fits
- Vintage, apparel, and electronics resellers cross-listing inventory across eBay, Etsy, Poshmark, Mercari, and Depop
- Boutique shops synchronizing single-SKU items between a Shopify storefront and peer-to-peer marketplaces
- Operators testing MCP and A2A commerce agents against real marketplace fee and mandate constraints
- Per-channel variant and fee engine computing exact platform commission, payment processing, and net payout across 7 marketplaces plus 2 local channels
- Pre-publish compliance guards enforcing Etsy's 20-year vintage/handmade rule and per-channel rate budgets
- Human Mandate state machine governing autonomous offer auto-accept, counter-offer, decline, and cross-channel sold-item delisting
- Agent-native MCP server (14 tools) and /.well-known/agent-card.json + /.well-known/oauth-protected-resource discovery endpoints
- Full verification harness (scripts/verify.sh) gating build, typecheck, lint, unit, contract, integration, security, operations, and Playwright E2E suites
Want something like this built?
Bring the job that eats your week. Step 1 is a free 15-minute fit call. Step 2 is the AI Staff Assessment, $500, a written assessment you keep. Step 3 is your first hire at a published price, or you take the assessment and stop.