Formal Skill: Programmable Runtime Skills for Efficient and Accurate LLM Agents

Fuente: arXiv
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Hauptverfasser: Zhang, Xi, Gao, Meijun, Zhao, Yuntian, Tan, Xinyu, Yao, Yilun, Wang, Feiyu, Wang, Yanshu, Dingsiyi, Yang, Tong
Format: Preprint
Veröffentlicht: 2026
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author Zhang, Xi
Gao, Meijun
Zhao, Yuntian
Tan, Xinyu
Yao, Yilun
Wang, Feiyu
Wang, Yanshu
Dingsiyi
Yang, Tong
author_facet Zhang, Xi
Gao, Meijun
Zhao, Yuntian
Tan, Xinyu
Yao, Yilun
Wang, Feiyu
Wang, Yanshu
Dingsiyi
Yang, Tong
contents Large Language Model (LLM) agents increasingly act inside real workspaces, where tools and skills determine whether model reasoning becomes reliable action. Existing skills remain largely informal: Markdown skills and instruction packs encode procedures as long natural-language documents, while function calling, Model Context Protocol (MCP) servers, and framework tools structure individual actions but usually leave workflow state, policy enforcement, and completion discipline outside the skill itself. We introduce Formal Skill, a runtime-native abstraction that represents reusable capability with JSON metadata and action schemas, reliable Python executors, hook-governed control logic, Formal Skill routing, and skill-local runtime state. By moving reusable procedure from repeated prompt text into executable state machines and hook policies, Formal Skill gives agents a token-efficient and enforceable control surface. We implement the abstraction in FairyClaw, an open-source event-driven runtime for executable, observable, and composable Formal Skills. On Harness-Bench, FairyClaw obtains highly competitive average scores while using substantially fewer tokens, with especially strong results on tasks that expose the role of Formal Skill.
format Preprint
id arxiv_https___arxiv_org_abs_2605_19604
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Formal Skill: Programmable Runtime Skills for Efficient and Accurate LLM Agents
Zhang, Xi
Gao, Meijun
Zhao, Yuntian
Tan, Xinyu
Yao, Yilun
Wang, Feiyu
Wang, Yanshu
Dingsiyi
Yang, Tong
Artificial Intelligence
Large Language Model (LLM) agents increasingly act inside real workspaces, where tools and skills determine whether model reasoning becomes reliable action. Existing skills remain largely informal: Markdown skills and instruction packs encode procedures as long natural-language documents, while function calling, Model Context Protocol (MCP) servers, and framework tools structure individual actions but usually leave workflow state, policy enforcement, and completion discipline outside the skill itself. We introduce Formal Skill, a runtime-native abstraction that represents reusable capability with JSON metadata and action schemas, reliable Python executors, hook-governed control logic, Formal Skill routing, and skill-local runtime state. By moving reusable procedure from repeated prompt text into executable state machines and hook policies, Formal Skill gives agents a token-efficient and enforceable control surface. We implement the abstraction in FairyClaw, an open-source event-driven runtime for executable, observable, and composable Formal Skills. On Harness-Bench, FairyClaw obtains highly competitive average scores while using substantially fewer tokens, with especially strong results on tasks that expose the role of Formal Skill.
title Formal Skill: Programmable Runtime Skills for Efficient and Accurate LLM Agents
topic Artificial Intelligence
url https://arxiv.org/abs/2605.19604