Choosing an Agent Harness Is Now an Architecture Decision

UHP and HarnessRouter make agent runtimes easier to compare and integrate. The engineering challenge is proving which configuration deserves production traffic.

Consider a document agent that finishes its task, returns valid JSON and produces the expected report.

On the dashboard, the run is green. During review, someone notices that two findings refer to sections that do not exist in the source document.

Now try the same task through another agent runtime. It uses the same model but reads the files differently, makes fewer tool calls and produces a different result.

Which system should the product use? The cheaper one, the faster one or the one that survives the review?

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This is the architectural question behind the recent interest in harness engineering.

Model selection remains important, but a production agent also depends on the machinery around the model: its execution loop, tools, context management, permissions, workspace and recovery behaviour.

The Unified Harness Protocol or UHP, gives applications a common way to drive that machinery.