HarnessRouter

HarnessRouter is a Y Combinator-backed API platform that lets developers embed production-grade AI agents—Codex, Claude Code, Hermes, and more—directly into their products without building or maintaining the underlying agent infrastructure. Instead of spending months wiring up sandboxes, runtimes, tool orchestration, and streaming, developers get a single API key and a drop-in AGENTS.md guide that a coding agent can use to wire the integration automatically.

What It Is

HarnessRouter sits between your product and the world's leading AI agents. It provides what the company calls a "harness"—the full execution layer around a model, including instructions, model policy, tools and MCP, skills, runtime and sandbox, permissions and guardrails, and an output contract. The result is that your users receive finished artifacts (videos, codebases, documents, images, game files) rather than raw model text, all without leaving your product.

How the Three-Step Workflow Works

The integration path is designed to be completed by a coding agent, not manually:

• Step 1 – Drop in AGENTS.md: Copy the official HarnessRouter instructions and paste them into Codex, Claude Code, or another coding agent.
• Step 2 – Describe your feature: Tell the coding agent what you want to build (e.g., "Build a contract-review app that lets users upload an agreement, streams progress, and renders the result").
• Step 3 – Add your API key securely: When the coding agent opens a secure secret modal, create a Workspace API key and paste it in. The agent stores it as HR_API_KEY and completes the build.

The demos on the site were built exactly this way, according to the product page.

Harness Architecture and Agent Roster

Each harness is a named, swappable configuration. Your integration code and output schema stay constant; switching from claude-code to codex requires only a one-line config change. Current harnesses include:

• Codex – Code, apps, and images
• Claude Code – Code, files, and documents
• Hermes – Autonomous tasks across any frontier model
• Pi – Coding agent (listed as "Soon")

The platform handles sandboxing per run, agent runtime, tool orchestration, files and artifacts, sessions and streaming, retries and timeouts, permissions, and cost controls—the full list of infrastructure concerns the product page describes as taking months to build in-house.

Control and Observability

HarnessRouter provides a trace view that shows every task broken down step by step, including event timelines with timestamps, tool calls, file changes, and final result artifacts. Operators can configure each harness individually and set budgets, alerts, and hard caps so production usage stops at a defined limit.

Why It Got Attention

HarnessRouter was ranked #5 Product of the Day on Product Hunt at launch. The product is backed by Y Combinator and lists a launch partner (TokenRouter). The homepage lists several organizations as users, including Epsilla, Hibo, Readily, Spira AI, and Stanford Medicine—these are vendor-published claims on the product page.

Update: Active Launch Phase

The product is in active launch mode with a 7-day card-gated trial available. The pricing page notes that checkout shows $0 today with the renewal date and selected plan visible before commitment. The platform roadmap includes at least one additional harness (Pi) listed as "Soon," signaling ongoing agent roster expansion.