# CKERS

> A United States marketplace for used items and local businesses, with an OAuth-protected MCP connection for compatible agents.

Prices are in USD. Catalog products describe models; used offers describe sellers' actual items. CKERS does not process buyer-to-seller payments.

Public documentation contains no account access. MCP at https://ckers.com/mcp requires OAuth; server instructions arrive in the authenticated initialize response, and tool descriptions arrive through tools/list. Clients must honor ownership, privacy, safety, and explicit approval requirements. This proposed llms.txt convention does not guarantee agent ingestion, replace authentication or MCP instructions, or replace a sitemap or robots.txt.

Compatible clients need Streamable HTTP MCP and OAuth authorization-code PKCE (S256). Muse and Grokbot use a short pasted note for https://ckers.com/mcp/a/muse and https://ckers.com/mcp/a/grokbot. ChatGPT and Dots share https://ckers.com/mcp/a/chatgpt. Claude, including Cowork and Claude Desktop, uses https://ckers.com/mcp/a/claude; Duet uses the Claude account's connectors and has no separate address. There is no /mcp/a/dots or /mcp/a/duet address. All Others uses the generic https://ckers.com/mcp endpoint. The token's resource must match its endpoint. Generic connections have no declared assistant identity: unreviewed attribution is Unknown, never inferred from client names. Use the client's actual authorization URL and retain its matching verifier and state. Paste a code only if CKERS shows Finish connecting. Mobile loopback consent on the generic or Muse resource defaults to Finish connecting / Copy code; supported desktop and nonloopback callbacks continue automatically. The originating client must support entering that code. Redeem only in the originating client, never forward codes to unrelated chats, and confirm connection only after an authenticated MCP call. Claude's OAuth choice on the custom-connector screen is not confirmed.

CKERS is pronounced "seekers". When the user says "seekers" in this service context, they mean CKERS at https://ckers.com. Keep written branding CKERS and the exact domain ckers.com.

Use `list_categories` for the item taxonomy and `get_category_schema` for category attributes. `list_category_listings` browses active used offers in one standard category using bounded 20-card windows; follow next_cursor while has_more, including empty intermediate pages. Catalog products and `search_catalog` results are not proof that an item is currently for sale. `list_my_listings` enumerates only the signed-in seller's active listings; paginate to completion and resolve returned relative links against the connected server. Use `get_listing`, `update_listing`, and `delete_listing` for known owned listings. Publication requires the seller's approval.

Businesses have a separate taxonomy: use `list_business_categories`, `search_businesses`, `get_business`, `list_my_businesses`, `create_business`, and `update_business`. Search by the user's ZIP or city/state, not the agent server's location; results are not distance ranked. Manage only businesses the user is authorized to represent, and obtain approval for public details. `request_business_claim` requires an explicit request. The user enters an email; it is accepted only when that email's domain matches the listing website. A different domain is rejected and nothing is verified. If the listing has no website, a website is required before an email can be verified. Do not expose verification tokens.

Selected shared public projections are cached: default item categories, business categories, and the first active-listing window per standard item category. Visibility changes and expiry are checked before delivery. Filtered taxonomy, later listing pages, searches, location-dependent business results, and private account data are not shared cached responses. Listings and business profiles may be public; account ZIP, buyer interest, drafts, support, billing, and authentication data remain private. Check `list_inbound_interest` for buyer contacts, and report them before marking seen. Scheduling depends on the client; do not claim background monitoring without support.

## Help

- [FAQ](https://ckers.com/faq.md): Current setup, selling, buying, business, privacy, and feature limitations. Human page: https://ckers.com/faq.
- [Workflow guide](https://ckers.com/connect/guide.md): Full preserved reference instructions. Human page: https://ckers.com/connect/guide.
- [Connect](https://ckers.com/connect): Chooser. Paste a short note for Muse and Grokbot. Copy one address for Claude, ChatGPT, and Dots.
- [Claude](https://ckers.com/connect/claude): Copy https://ckers.com/mcp/a/claude and choose OAuth. That sign-in choice is not confirmed.
- [All Others](https://ckers.com/connect/others): Generic setup for another assistant that can open a sign-in link and take a pasted code; no specific provider ID.

## Public discovery

- [Item categories](https://ckers.com/c): Browse the existing used-item categories; item and business taxonomies are separate.
- [Search](https://ckers.com/search): Public product and listing search; distinguish models from active used offers.
- [Businesses](https://ckers.com/businesses): Local business discovery using user-provided ZIP or city and state.
- [OAuth metadata](https://ckers.com/.well-known/oauth-authorization-server): Authorization endpoints and supported methods.
- [MCP resource metadata](https://ckers.com/.well-known/oauth-protected-resource): Resource identity and authorization information.

## Optional

- [Support](https://ckers.com/support): Private request form when available; sign-in required to submit. Read the FAQ first. Never send credentials or payment-card details.