Building an agent often starts with one model call and turns into a stack for runtime, tools, memory, retrieval, UI, observability, sandboxing and evaluation. AgentsKit brings those pieces together as 25 focused JavaScript packages on a 5 KB, zero-dependency core. Use only what you need, keep the contracts visible, and replace providers or infrastructure without rewriting the application. The open-source ecosystem also includes Chat, Registry, Doc Bridge, Playbook and Code Review. MIT licensed.
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Maker
š
š Emerson here, solo maintainer.
Short story. Earlier this year I tried to build a simple AI chat in JavaScript ā streaming, 2 tools, memory across sessions. Not curing cancer, just a chat.
I ended up gluing 5 libs together:
⢠Vercel AI SDK for chat (no runtime)
⢠LangChain.js for runtime (200MB, leaky abstractions)
⢠assistant-ui for components (53 of them)
⢠MCP for tool interop (no UI)
⢠Pinecone bolted on
3 days in, couldn't debug it. 5 days in, deleted everything.
6 months later ā AgentsKit.
What's different:
ā 10KB zero-dep core, bundle gates in CI
ā 6 formal contracts (Adapter, Tool, Memory, Retriever, Skill, Runtime) ā published as ADRs, not magical abstractions
ā Same `useChat()` works in React AND terminal (Ink)
ā Swap providers in 1 line ā 8+ adapters, one contract
ā Built-in: tools, memory, RAG, sandbox, observability, eval
ā `npx agentskit init` scaffolds a working agent in 30 seconds
Shipping now (v1.0):
⢠14 packages on npm, 538 tests
⢠Full docs at agentskit.io
⢠4 starter templates (react, ink, runtime, multi-agent)
Shipping Phase 2 this month:
⢠Deterministic replay for LLM calls (record seed + responses, reproduce bit-for-bit)
⢠Prompt diff tool (git blame for prompts)
⢠Time-travel debugger (rewind traces, alter tool outputs, re-run)
⢠Token budget compiler
Honest comparison:
⢠vs Vercel AI SDK ā their chat UI rules, their runtime is missing
⢠vs LangChain.js ā 200x smaller, no leaky abstractions
⢠vs Mastra ā solid runtime, we cover more surface (browser + terminal + CLI)
⢠vs MCP ā we consume MCP servers; MCP is a protocol, AgentsKit is the kit
Free, MIT, built in the open. No cloud signup. No telemetry you can't turn off.
Links:
š https://www.agentskit.io
š» https://github.com/EmersonBraun/...
š¬ https://discord.gg/zx6z2p4jVb (Office Hours every Friday)
Brutal feedback welcome ā especially where the pitch overclaims or where position vs the ecosystem is unclear. Will be here all day š