Kestrel

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KestrelEverything is a plugin.

A kernel, an agent runtime and a plugin host behind one small protocol. Run agents on any desktop OS or orchestration platform; drive them from a browser, desktop shell or phone.

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Read the architecture
Kestrel

Plugin-first, all the way down

Models, tools, memory, MCP servers and user interfaces attach through the same lifecycle. A plugin can inject another plugin's service without importing its code.

Headless by design

The agent runtime is a library. The HTTP/SSE server, CLI and web console are clients, so the same brain can run on a laptop, a Docker container or a Kubernetes pod.

Streaming, resumable sessions

Every run emits typed events. Clients resume from the last event id, render tool calls live and approve risky actions out of band.

Delegation you can bound

A parent hands one task—or a batch of independent ones—to subagents with fresh contexts, roles and step budgets. Concurrency, depth and wall clock are capped, and every child is a session you can inspect.

Boring where it matters

No hidden globals, no implicit ordering. Services are explicit, disposers are tracked, and one broken plugin cannot take down the host.

One runtime, many shapes ​

bash
# Anywhere Node 22 runs
pnpm install && pnpm build
KESTREL_PLUGINS=plugins,examples/plugins node apps/server/dist/bin.js

# Or a container
docker build -t kestrel . && docker run --rm -p 7331:7331 -v "$PWD:/workspace" kestrel

The server exposes a small REST surface plus an event stream. The bundled console is a static application: it can be served by the agent host, by a CDN, or wrapped by a desktop or mobile shell without changing a line of agent code.

What "plugin" means here ​

ConcernPluginContract
Model access@kestrel/plugin-openai, @kestrel/plugin-anthropicprovide models
Filesystem and shell tools@kestrel/plugin-tools-coreprovides tools
Durable notes@kestrel/plugin-memoryinjects tools, provides memory
Model Context Protocol@kestrel/plugin-mcpinjects tools, provides mcp
Skills@kestrel/plugin-skillsinjects prompts, tools, provides skills
Delegation@kestrel/plugin-subagentsinjects sessions, tools, prompts, provides subagents
Your productanything in plugins/whatever you declare

There is no privileged core plugin. tools-core is simply the plugin that happens to ship with the repository. Removing it yields an agent that can still talk, but cannot touch the workspace.

Where to go next ​

  • Quickstart — run the server and console in five minutes.
  • Architecture — how the kernel, runtime and transport fit together.
  • Writing a plugin — add a tool, a provider or a whole subsystem.
  • Protocol — build a client in any language.

Released under the MIT License.

Kestrel contributors