Web Agents Don't Need a Browser

Web agents that operate websites through graphical interfaces are widely used but suffer from security risks, unconstrained and unpredictable side effects, and high latency and cost. This makes them inherently unsuitable for workloads that modify data, handle sensitive information, or issue large numbers of queries. We present Indices, a system that uses coding agents to learn the message format between a web application and its backend. Once learned, the resulting connectors issue only the necessary network requests directly to the server, avoiding the browser UI entirely. Connectors are expressed in Indescript, a limited DSL and runtime that enforces least privilege by construction and mediates all network effects. Indices supports both read and write actions on authenticated endpoints, and in production has generated over 400 connectors processing over a million requests per month. Across 10 real-world workflows, connectors run 43$\times$ and 20$\times$ faster on average than Claude (Opus 5) and Codex (GPT 5.6 Sol) browser agents. We describe the architecture and runtime, and argue that for state-changing and record-retrieval workloads, web agents do not need a browser.