COSPEC: A Specification Elicitation Framework for Context Co-Construction with LLMs

Vibe coding uses repeated natural-language prompts and minimal code review in large language model (LLM)-based development. Development may end before sufficient client–LLM context co-construction occurs. We propose CO-constructed SPECification (COSPEC), combining Joint Application Development facilitation with Specification by Example. Within a four-stage cycle, the LLM presents prototype scenarios for client review and records approved scenarios as Given–When–Then (GWT) specifications. An automated exploratory evaluation used an LLM client given a reference specification and engagement policies. We conducted 150 runs across five conditions involving COSPEC, GitHub Spec Kit-based Spec-Driven Development (SDD), and vibe coding, varying Claude/Codex role assignments and Maker reasoning levels. Dialogues and artifacts showed client-role revision requests and acceptance reflected in scenarios and GWT specifications. Mean requirements coverage through co-construction favored SDD under diligent engagement and COSPEC under satisficing engagement; significant method differences were limited to particular requirement categories and Judges. Both methods covered more requirements through co-construction under diligent engagement. These observations support the feasibility of delegating specification writing to the LLM while involving clients through repeated responses. However, presentation medium and procedure varied together, preventing isolation of their effects. Whether this supports sustained human participation requires human evaluation.