# How the Caveman-Commit Command Generates Short Conventional Commit Messages > Discover how the caveman-commit command generates short Conventional Commit messages by routing diffs through a language model with strict formatting rules. Learn more. - Repository: [Julius Brussee/caveman](https://github.com/JuliusBrussee/caveman) - Tags: how-to-guide - Published: 2026-07-07 --- **The `/caveman-commit` command generates terse Conventional Commit messages by routing diffs through an LLM constrained by strict formatting rules defined in [`skills/caveman-commit/SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/skills/caveman-commit/SKILL.md).** The `caveman-commit` command in the JuliusBrussee/caveman repository transforms staged diffs into compact, conventional commit messages through a deterministic LLM-driven pipeline. Unlike generic commit generators, this skill enforces brevity and strict formatting via an explicit rule set rather than relying on model temperature settings. Understanding how the `caveman-commit` command generates short conventional commit messages reveals a pattern of using structured prompts to constrain LLM outputs for developer tooling. ## Triggering the Caveman-Commit Skill The skill activates when a user types `/caveman-commit` or includes trigger phrases like "write a commit", "commit message", or "generate commit" in their prompt. According to [`skills/caveman-commit/README.md`](https://github.com/JuliusBrussee/caveman/blob/main/skills/caveman-commit/README.md), this invocation signals the system to enter "commit" mode and prepare the diff context for processing. ## The Rule-Based LLM Prompt Architecture The core generation logic resides in [`skills/caveman-commit/SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/skills/caveman-commit/SKILL.md), which acts as a contract between the user and the LLM. This file supplies the model with explicit constraints that override default verbose tendencies. ### Subject Line Constraints As specified in lines 14-20 of [`SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/SKILL.md), the subject line must follow the format `(): `, where type is one of the standard Conventional Commits types such as `feat` or `fix`. The rules enforce: - **Length limits:** 50 characters preferred, with a hard limit of 72 characters (line 18) - **Style requirements:** No trailing periods, no filler phrases like "This commit does...", and strict imperative mood (lines 15-18) ### Body Omission and Formatting Rules The skill aggressively omits the body section unless the change requires explanation. Per lines 22-25 of [`SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/SKILL.md), the body is included only when the "why" is not obvious, there are breaking changes, migration notes, or issue references. When present, the body must: - Wrap at 72 characters - Use dashes for bullet points - End with issue trailers such as `Closes #42` (lines 26-28) ### Explicit Exclusions To maintain professionalism and neutrality, [`SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/SKILL.md) explicitly forbids specific patterns. Lines 30-31 prohibit phrases like "This commit does X", first-person pronouns, and "As requested by...". Line 32 forbids AI attribution (e.g., "Generated with Claude Code"), while line 33 excludes emojis unless project conventions specifically require them. ## The Execution Pipeline The command flows through four distinct architectural components before returning the final message. ### Command Parsing and Routing The [`src/plugins/opencode/plugin.js`](https://github.com/JuliusBrussee/caveman/blob/main/src/plugins/opencode/plugin.js) file detects the `/caveman-commit` invocation and routes the request to the "commit" mode handler. This component extracts the diff context and prepares it for the skill engine. ### Mode Tracking and Skill Lifecycle The [`src/hooks/caveman-mode-tracker.js`](https://github.com/JuliusBrussee/caveman/blob/main/src/hooks/caveman-mode-tracker.js) manages the skill's activation state, ensuring the LLM is called only when the user is explicitly in commit mode. This prevents accidental commit message generation during unrelated conversations. ### LLM Generation and Output Formatting The LLM (Claude, Gemini, etc.) receives the diff alongside the rule set from [`SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/SKILL.md). As noted in lines 9-10 of the skill documentation, the system returns only the formatted commit message as plain text within a code block, without executing `git commit` or adding conversational filler. ## Practical Usage Examples ### Basic Commit Generation ```bash /caveman-commit ``` When executed with staged changes, the command returns a compact message like: ``` feat(api): add GET /users/:id/profile Mobile client needs profile data without the full user payload to reduce LTE bandwidth on cold-launch screens. Closes #128 ``` ### Handling Breaking Changes For breaking changes, the skill automatically includes the `!` marker and `BREAKING CHANGE` footer: ``` feat(api)!: rename /v1/orders to /v1/checkout BREAKING CHANGE: clients on /v1/orders must migrate to /v1/checkout before 2026-06-01. Old route returns 410 after that date. ``` ## Summary - The `caveman-commit` command uses [`skills/caveman-commit/SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/skills/caveman-commit/SKILL.md) to enforce strict formatting rules on LLM outputs - Subject lines follow `(): ` with a 50-character soft limit and 72-character hard limit - Body text is omitted by default unless breaking changes, migration notes, or issue references are present - The pipeline routes through [`src/plugins/opencode/plugin.js`](https://github.com/JuliusBrussee/caveman/blob/main/src/plugins/opencode/plugin.js) and [`src/hooks/caveman-mode-tracker.js`](https://github.com/JuliusBrussee/caveman/blob/main/src/hooks/caveman-mode-tracker.js) before LLM processing - Output excludes AI attribution, emojis, and first-person pronouns to maintain professional standards ## Frequently Asked Questions ### What is the maximum length for commit messages generated by caveman-commit? The subject line prefers 50 characters with a hard limit of 72 characters as defined in [`skills/caveman-commit/SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/skills/caveman-commit/SKILL.md) line 18. When included, the body wraps at 72 characters per line. ### Does caveman-commit automatically execute git commit? No. According to lines 9-10 of the skill specification, the command returns only the formatted message as plain text in a code block. The user must manually paste and execute the commit. ### How does caveman-commit handle breaking changes? The skill detects breaking changes and prepends the `!` indicator to the type/scope (e.g., `feat(api)!:`). It also includes a `BREAKING CHANGE:` footer in the body when migration notes or compatibility warnings are required, following the Conventional Commits specification. ### Can I customize the excluded phrases or allowed emojis in caveman-commit? The current rule set in [`SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/SKILL.md) hardcodes exclusions for first-person pronouns (lines 30-31), AI attribution (line 32), and emojis (line 33). Customization would require modifying the skill file in [`skills/caveman-commit/SKILL.md`](https://github.com/JuliusBrussee/caveman/blob/main/skills/caveman-commit/SKILL.md) to adjust the constraint parameters for your specific project conventions.