fast-agent vs harness-sdk
Python and TypeScript frameworks for building AI agents
fast-agent and harness-sdk help developers build and run LLM agents, connect tools, and compose multi-agent workflows. fast-agent focuses on Python configuration, MCP connections, and terminal workflows, while harness-sdk offers Python and TypeScript harnesses alongside lower-level SDKs for controlling agent execution.
fast-agent: Build and Run LLM Agents and Workflows
A Python framework and CLI for building, testing, and running LLM agents that use MCP tools and compose into workflows. It suits developers who want both interactive agent development and a programmable framework.
harness-sdk: Build and Run AI Agents in Python and TypeScript
Strands Agents provides Python and TypeScript tools for building AI agents, from a ready-made harness to a customizable agent SDK. It suits teams that want model flexibility and control over agent execution without a hosted control plane.
| fast-agent | harness-sdk | |
|---|---|---|
| Language | Python | Python |
| License | Apache-2.0 | Apache-2.0 |
| Stars | 3.9k | 8.6k |
| Forks | 446 | 1.3k |
| Last analyzed | Oct 7, 2026 | Oct 3, 2026 |
Key differences
- fast-agent is Python-only; harness-sdk supports Python and TypeScript.
- fast-agent emphasizes Python-defined agents, configurable workflows, MCP server connections, and an interactive terminal CLI. harness-sdk pairs ready-made harnesses with lower-level SDKs for configuring the agent loop.
- harness-sdk describes lifecycle controls such as turn limits, token budgets, cancellation, and stop reasons, as well as hooks and tracing. fast-agent highlights workflow composition and model and prompt evaluation.
- fast-agent can run agent applications as MCP servers or through ACP clients. harness-sdk describes agents running in your process without a hosted control plane.
- Both projects use the Apache-2.0 license. The provided repository figures are 3.9k stars and 447 forks for fast-agent, and 8.6k stars and 1.3k forks for harness-sdk.
Choose fast-agent if you…
- need a Python framework with an interactive terminal CLI and configurable agent workflows.
- want to connect agents to MCP servers or run agent applications as MCP servers or through ACP clients.
- plan to define agents and workflows in Python, including chains, routers, and parallel fan-out.
Choose harness-sdk if you…
- want a ready-made harness or a lower-level SDK in Python or TypeScript.
- need control over agent execution with lifecycle limits, hooks, tracing, or guardrails.
- want configurable defaults for models, tools, memory, sessions, and context management.
Compare the numbers side by side, or add more projects
This comparison is generated with AI from the OSRepos analyses of both projects. Always check each project's repository and documentation before choosing.