jmap-kit

A typed TypeScript library for building JMAP clients. It handles session discovery, request building with type-safe invocation factories, response dispatching, file operations, and a plugin system for validation and transformation — so you can focus on your application instead of the protocol.

See the complete jmap-kit Documentation.

Using jmap-kit

Features

• Session management: automatic discovery via .well-known/jmap, session state tracking, staleness detection
• Type-safe invocations: factory functions for every JMAP method, with compile-time enforcement of argument types and property names
• Result references: chain dependent method calls within a single request without extra round trips
• Request building: combine multiple method calls into one request with automatic capability URI inclusion and ID management
• Response dispatching: route responses to handlers by method name, data type, or invocation ID
• File operations: upload and download with server limit enforcement and automatic concurrency control
• Plugin system: validation and transformation hooks at each stage of request processing
• Server limit enforcement: built-in validators for maxObjectsInGet, maxObjectsInSet, maxCallsInRequest, maxSizeRequest, and read-only accounts
• Extensible: define custom capabilities with their own types, invocations, validators, and transformers

Installation

npm install jmap-kit
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yarn add jmap-kit
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pnpm add jmap-kit
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Quick Example

import { JMAPClient, EmailCapability, Mailbox } from "jmap-kit";

const transport = /* your HTTP transport (see Developer Guide) */;
const client = new JMAPClient(transport, { hostname: "api.example.com" });
client.registerCapabilities(EmailCapability);

await client.connect();

const accountId = client.primaryAccounts["urn:ietf:params:jmap:mail"];

// Query for the Inbox, then fetch it — in a single request
const query = Mailbox.request.query({
    accountId,
    filter: { role: "inbox" },
});

const get = Mailbox.request.get({
    accountId,
    ids: query.createReference("/ids"),
    properties: ["id", "name", "role", "totalEmails", "unreadEmails"],
});

const request = client.createRequestBuilder().add(query).add(get);
const response = await request.send();

await response.methodResponses.dispatch({
    "Mailbox/get": (invocation) => {
        const mailboxes = invocation.getArgument("list");
        console.log("Inbox:", mailboxes);
    },
    error: (invocation) => {
        console.error("Error:", invocation.type);
    },
});

await client.disconnect();
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Documentation

See the Developer Guide for comprehensive documentation covering session management, capabilities, invocations, request building, response handling, file operations, customisation, the plugin system, and creating custom capabilities.

Development

Setup

git clone <repository-url>
cd jmap-kit
yarn install
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Scripts

Command	Description
yarn test	Run tests in interactive watch mode (Vitest)
yarn test --run	Run all tests once (CI)
yarn format:check	Check Prettier formatting
yarn lint	Run ESLint (--fix to auto-fix)
yarn typecheck	Type-check without emitting files
yarn build	Compile TypeScript
yarn bundle	Build bundles with Rollup (for analysis, not shipped)
yarn size-check	Bundle and print file sizes
yarn docs	Generate API docs with TypeDoc

Contributing

Contributions are welcome! See the Contributing Guide for development setup, conventions, and PR guidelines.

Roadmap

jmap-kit currently implements the JMAP Core (RFC 8620), Mail (RFC 8621), and Blob Management (RFC 9404) specifications, plus the FastMail Masked Email extension. The following features are planned for future minor releases.

Core specification features

• PushSubscription (RFC 8620 Section 7.2) — PushSubscription/get and PushSubscription/set methods for managing push notification subscriptions
• EventSource (RFC 8620 Section 7.3) — built-in client for server-sent events, including connection management and automatic reconnection (URL generation via getEventSourceUrl() is already available)

Additional JMAP capabilities

Support for capabilities defined in other published and draft JMAP specifications is planned, including:

• Quotas — RFC 9425
• Contacts — RFC 9610
• Sieve Scripts — RFC 9661
• Principals and Sharing — RFC 9670
• MDN (Message Disposition Notification) — RFC 9007
• S/MIME Signature Verification — RFC 9219
• WebPush VAPID — RFC 9749
• Calendars — Draft IETF JMAP Calendars
• Tasks — Draft IETF JMAP Tasks

Any of the above capabilities can be implemented as custom capabilities using the plugin system. Contributions are welcome!

Other specifications

• JMAP over WebSocket — RFC 8887.

License

MIT License