jira.js is a comprehensive TypeScript SDK for Atlassian Jira REST APIs, covering Cloud, Data Center, Agile, Service Management, Assets, Administration, Teams, User Management, and User Provisioning surfaces. It is designed as a modular library with separate client factories (e.g., createCloudClient, createServerClient, createAgileClient) that provide typed access to hundreds of API endpoints. The architecture is built on a core transport layer that handles authentication (basic, bearer, OAuth 2.0), request/response validation using Zod schemas, error classification, retry logic, and multipart form data. Every API response is validated at runtime, with configurable behavior on schema mismatch (warn, throw, silent) and an optional audit mode to detect API drift. The library is primarily generated from Atlassian's OpenAPI specifications, resulting in a large, consistent codebase with models, parameters, and API functions organized by product domain. Key entry points include the client factories and subpath imports like 'jira.js/cloud' or 'jira.js/agile'. Data flows are straightforward: consumers construct typed request options and call client.sendRequest(), which returns validated response objects. External dependencies are minimal: zod for runtime validation, and the platform's fetch API for HTTP. The library also includes webhook signature verification, OAuth 2.0 (3LO) helpers for both Cloud and Data Center, and a browser-compatible bundle. Notable patterns include the use of apiObject and openEnum helpers to create Zod schemas that are permissive by default but strict under audit, enabling graceful handling of API evolution. The error hierarchy uses branded symbols for reliable type guards across package copies. The test suite includes extensive live integration tests against real Atlassian instances, with resource tracking and entitlement-aware gating. Overall, jira.js is a well-engineered, actively maintained SDK that prioritizes type safety and runtime validation, though its large generated surface introduces some duplication and maintenance overhead.