Controlled Czech is an open specification for clear, unambiguous and information-dense technical Czech, packaged as a skill. Use it when writing, editing or reviewing Czech documentation, specifications, ADRs, issues, pull request descriptions, runbooks and AI agent instructions. Every rule has a stable identifier (CCxxx), so the agent can load a single rule instead of the whole specification and every suggestion can be traced back to it. Only the skill description enters the context up front; the full rules load when Czech text is actually being written. The repository also ships a deterministic linter written in Go (controlled-czech check). It runs offline, uses no LLM and never rewrites text, so the same rules can gate documentation in CI with --fail-on-warning. Not intended for marketing copy, fiction, personal communication or brand voice.