Beyond Static Endpoints: Tool Programs as an Interface for Flexible Agentic Web Services

2026-06-18

AI Summary

Existing tool interfaces based on static endpoints struggle to express long-running workflows involving complex control flows such as loops, conditional branches, and retries. This work proposes replacing static endpoints with executable tool programs, enabling explicit effect typing and sophisticated workflow control through constraint-guided program construction, effect-aware exactly-once replay mechanisms, and configuration-driven execution policies. Implemented atop MCP-style services and a WebAssembly sandbox, the system demonstrates significant performance improvements in real-world scenarios, reducing end-to-end latency by up to 53.4% and client-side traffic by as much as 96.1%, with particularly pronounced gains under high network latency or increased workflow complexity.

Abstract

In the agentic web era, LLM-based agents increasingly invoke web services as tools, yet most interfaces remain \emph{static endpoints} that poorly express long-horizon workflows with loops, conditionals, joins, and retries. We present ToolPro, which represents an agent's tool intent as an \emph{executable tool program} that compactly encodes multi-step service interactions with explicit effect types. ToolPro combines constraint-guided program construction, effect-aware replay for exactly-once state-modifying calls, and a profile-driven policy that decides when program execution outperforms stepwise calling. We instantiate ToolPro over MCP-style services with WebAssembly sandboxing and evaluate it on diverse workflows of real-world applications. ToolPro reduces end-to-end latency by up to 53.4\% and client-side traffic by up to 96.1\%, with larger gains under higher network latency and workflow complexity.

Problem

• static endpoints
• agentic web services
• long-horizon workflows
• tool interfaces
• web service composition

Innovation

• tool programs
• agentic web services
• exactly-once execution
• constraint-guided synthesis
• effect-aware replay