A microkernel for AI coding agents. Models, tools, memory, project-context conventions, and even the UI are versioned, independently-installable plugins — wired together with a real, typed configuration language, not a bespoke config format.

A small, stable core that does almost nothing on its own, plugins that do everything, a plan/apply gate before anything mutates, and a registry so anyone can ship a plugin without touching the core.

• Providers, not a monolith. LLM vendors, tools, long-term memory, repo-convention readers, and the frontend/UI are all separate, versioned plugins running as isolated subprocesses — crash-isolated, independently releasable, and not limited to any one implementation language.
• A real configuration language. Typed, schema-validated config that every plugin's settings go through — not a YAML subset with extra steps.
• Plan/apply for tool calls. Mutating operations get gated behind a diff and approval before they run; read-only operations execute freely. Policy is a first-party rule engine, not bolted on.
• A source-addressed registry, not a package index. Plugins are addressed directly by source repository and version-constrained, so publishing is just tagging a release.
• Replay is a first-class citizen. Every session is a durable, queryable record; old sessions render using the exact plugin versions that produced them, not whatever's currently installed.

Early. The core harness (working repo: agent) is in the specification and design phase — protocol contracts for each provider category, grounded in cross-harness research, are being settled before implementation starts. If you're looking for something to run, there isn't one yet; if you're interested in the design, that's the best place to dig in and the best time to raise an issue if something looks wrong or underspecified.

Copyright 2026 PluggableHarness.ai

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.