Web application developer Jobs in Seattle, WA

The future of software development is agentic. AWS is building Kiro — a frontier AI-powered development environment that autonomously tackles development tasks, maintains context across interactions, and continuously learns from its work. Kiro is already transforming how developers build and maintain software, and we're just getting started.

We're looking for a Software Development Engineer to build the server-side systems that power Kiro Web — a local web application that manages multiple AI agent sessions through the Agent Client Protocol (ACP). You'll own the backend that spawns, orchestrates, and communicates with kiro-cli processes, handling JSON-RPC 2.0 messaging over stdin/stdout, WebSocket fan-out to connected browsers, and the REST APIs that enable multi-agent team coordination.

The challenges are systems-level and novel: managing a pool of AI agent child processes with independent lifecycles, building a WebSocket gateway that multiplexes real-time notifications from dozens of concurrent sessions, implementing tool approval interception and relay, and designing the inter-agent communication layer that lets orchestrator agents delegate work to specialized agents via REST. You'll also build the distribution infrastructure that delivers Kiro to millions of developers — multi-platform builds, CDN-backed metadata services, and update delivery mechanisms.

Your impact spans both the local development experience and global distribution. Every developer managing AI sessions through the Kiro Web UI depends on your server layer. Every developer downloading Kiro for the first time uses your distribution systems.

This is your chance to build the engine behind the agent that builds the future.

Key job responsibilities
- Build and maintain the Kiro Web server (Fastify/Node.js/TypeScript) — session manager, ACP client adapter, WebSocket gateway, and REST API
- Implement the process-per-session architecture: spawning kiro-cli ACP child processes, managing JSON-RPC 2.0 communication over stdin/stdout, and handling lifecycle events (crash recovery, session resume, stale PID handling)
- Build the multi-agent team orchestration layer — team session lifecycle, inter-agent prompt routing with topology validation, parallel dispatch, and skill injection
- Design and implement the WebSocket fan-out system that multiplexes notifications from multiple ACP processes onto browser clients, tagged by session/team/role
- Build and operate Kiro's multi-platform distribution system — metadata services, platform detection, CDN configuration (CloudFront), custom channel authorization, and release automation
- Implement tool approval interception: hold execution when agents request permissions, emit approval requests to the frontend, and relay user decisions back to the agent
- Write comprehensive tests, build monitoring/alerting, and participate in on-call rotations
- Contribute to API design, architecture reviews, and team technical direction

About the team
Kiro Web builds the web-based experiences and platform services for Kiro. Our server layer is the bridge between browser UIs and kiro-cli's Agent Client Protocol — we spawn and manage AI agent processes, multiplex their real-time output to the browser via WebSocket, and orchestrate multi-agent teams through REST APIs. We also own the distribution platform that delivers Kiro builds worldwide via CloudFront. Tech stack: TypeScript, Node.js 22, Fastify, WebSockets, JSON-RPC 2.0, pnpm monorepo. The team is between Seattle and Portland, shipping weekly.

BASIC QUALIFICATIONS

- 3+ years of non-internship professional software development experience
- 2+ years of non-internship design or architecture (design patterns, reliability and scaling) of new and existing systems experience
- 1+ years of software development engineer or related occupational experience
- 1+ years of designing and developing large-scale, multi-tiered, multi-threaded, embedded or distributed software applications, tools, systems, and services using: C#, C++, Java, or Perl experience
- 1+ years of Object Oriented Design experience
- Bachelor's degree or foreign equivalent in Computer Science, Engineering, Mathematics, or a related field
- Experience programming with at least one software programming language

PREFERRED QUALIFICATIONS

- 3+ years of full software development life cycle, including coding standards, code reviews, source control management, build processes, testing, and operations experience
- Bachelor's degree in computer science or equivalent

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