caveman — 98,000 stars, and two people checked
"Why use many token when few token do trick." A Claude Code skill that instructs the model to answer in clipped, article-free prose, plus — since Monday — a local proxy and a Go compression engine underneath it. It plugs into Claude Code, Codex, Gemini, Cursor, Windsurf, Cline and thirty-odd other agents, exposes five MCP tools, and ships TypeScript and Python SDKs. The claim in the repo description is 65% of tokens cut. It has 97,905 stars, 5,649 forks and 243 watchers, which is not a ratio an organically-followed repo produces, and it crossed our own pool on July 2 at which point we did not cover it. Today it is trending again at 263 stars a day and launching on Product Hunt, four months after the original Show HN took 904 points.
Here is what happened when people checked. Max Taylor ran 24 prompts across six categories through five arms — 120 scored responses, judged by a separate Claude against per-prompt rubrics for required facts, required terms and dangerous wrong claims. Baseline output: 636 tokens. Prepending the words "be brief." to the prompt: 419 tokens, a 34% cut. Caveman lite: 401. Caveman full: 404. Caveman ultra: **449** — worse than the two-word prompt. Quality across every arm landed within 1.5 points (0.985 baseline, 0.985 "be brief.", 0.975 full) with zero safety violations. His conclusion: "the value isn't compression. It's structure." In July, JetBrains ran their own test and got 8–10% savings with no measured quality degradation. And the honest part is that caveman's own documentation does not really dispute any of it: the README states the skill adds ~1–1.5k input tokens per turn and that "on already-terse workloads they can go net-negative," and HONEST-NUMBERS.md goes further, disclosing that Copilot's per-request billing makes the tool useless by construction ("A shorter answer is the same request"), and that one Cursor A/B measured **4.3M tokens with caveman versus 1M without, and double the wall-clock time**. It publishes a break-even rule that tells you to turn it off. The best comment on the JetBrains thread explains the whole gap in one line: "the bulk of my token usage is not what I type in — it's that data the AI is processing for me."
Reach for it if you want consistent, structurally terse agent output and will A/B it against your provider's actual usage page, which is the only test the maintainer himself endorses. Delete the assumption that a compression tool's headline number describes your bill. Tradeoffs: the 65% figure is output tokens only on the vendor's own 10 tasks, ranging 22–87%, and output tokens are the cheap end of most agent workloads; the counterfactual 33.2% input-token figure comes from 54 runs across 18 test cases, published as a number rather than as raw runs; the license is split — MIT for the skill, CLI, SDKs and graders, BSL-1.1 for the engine, proxy, MCP binary and browser driver, converting to Apache-2.0 on 2030-06-21, with third-party hosted or embedded use requiring a commercial license; Taylor's benchmark is single-run per arm-prompt pair and he conceded in-thread that the variance findings may be noise; JetBrains tested at reasoning-low only; the v2.0.0 engine shipped Monday and the npm CLI was published two days ago, so the thing you install today is not the thing anyone benchmarked; and 476 open issues sit against those 243 watchers.
→ github.com/JuliusBrussee/caveman