A zero-dependency Python static analyzer called promptctl has been built to catch broken prompt signatures before deployment, addressing a common failure mode where renaming a variable in a prompt template—such as `{ticket}` becoming `{ticket_id}`—passes Git, unit tests, and code review but crashes every production call because call sites still pass the old variable. The tool performs three functions: PromptDiff detects variable changes in prompt files, Contract Validation verifies schema boundaries, and Impact Analysis traces where those variables are referenced across the codebase. It requires no LLM calls, no API keys, no model evaluations, and zero training, running strictly using Python’s built-in `ast`, `string.Formatter`, and set arithmetic directly against source code. Every terminal output and timing benchmark shown in the article comes from live runs of the tool. The article explicitly covers its limitations upfront. The tool is intended for those who ship prompt templates as code and have multiple callers formatting the same template. All source code, mock setup, and baseline snapshots are available on GitHub at https://github.com/Emmimal/promptctl.