The endpoint
A remote MCP server over Streamable HTTP. It speaks JSON-RPC 2.0 and works with any MCP client that supports OAuth. The tools run in the Kaption extension or desktop app on the user's own computer, so the user must have Kaption open.
Build on Kaption with MCP
Kaption exposes WhatsApp to AI apps and agents through one MCP server. This page lists every endpoint, document and repository you need.
MCP server address
https://mcp.kaptionai.com/mcpAuthentication
OAuth 2.1 with PKCE (S256) and dynamic client registration. There is one scope, kaption:access. Users sign in with their phone number and a code sent to them on WhatsApp, then choose how long the connection lasts. Access tokens expire after one hour. Calls without a token get HTTP 401 with a WWW-Authenticate header that points to the protected resource metadata.
Endpoints and documents
MCP endpoint
Streamable HTTP. An SSE endpoint is also available at /sse for older clients.
mcp.kaptionai.com/mcpOAuth metadata
Protected resource metadata (RFC 9728), which links to the authorization server.
mcp.kaptionai.com/.well-known/oauth-protected-resource/mcpOpenAPI description
OpenAPI 3.1 description of the HTTP endpoint, its OAuth scheme and error responses.
kaptionai.com/openapi.jsonMCP server card
Name, remotes, package and auth details in the MCP Registry server.json format.
kaptionai.com/.well-known/mcp.jsonAPI catalog
RFC 9727 linkset that lists the services on this domain.
kaptionai.com/.well-known/api-catalogllms.txt
A plain-text guide to the site for AI agents: what Kaption does and when to use it.
kaptionai.com/llms.txtLocal MCP server
The npm package for clients that run local servers. Needs Node.js 18 or newer.
www.npmjs.com/package/@kaptionai/mcp-extensionRelay source code
The cloud relay's source code is public. Every deploy is signed and recorded in a public log.
github.com/Kaption-AI/mcp-extension-remote
Tools
The cloud server exposes these tools. None of them sends a message immediately: the AI can leave a draft or schedule one message to one person. Chats the user locked in WhatsApp are never visible.
querylist_contactsget_contactget_contact_groupslist_groupsget_groupexport_contactsdownload_mediaget_analyticssummarize_conversationmanage_chatmanage_remindersmanage_listsmanage_labelsmanage_notesmanage_scheduled_messagescall_recordings
Limits
- Tools only work while the user has Kaption open: WhatsApp Web with the extension, or the desktop app.
- Access is rate-limited. Bulk or unsolicited messaging is against the terms.
- A scheduled message goes to one person and is at most 800 characters.
Security
Report vulnerabilities privately to security@kaptionai.com. Please do not open a public issue.
Questions
Is there a REST API?
Kaption's public interface is the MCP server. The OpenAPI file describes that HTTP endpoint so tools that read OpenAPI can find it; the operations themselves are MCP tools called over JSON-RPC.
Can I list the tools without signing in?
No. Every call, including initialize and tools/list, needs a token. The tool names are listed on this page and in the server card.
Which clients work?
Claude, ChatGPT, Cursor and other clients that support remote MCP servers with OAuth. Clients that run local servers can use the npm package instead.