Your AI agent forgot what failed. Vexen didn't.
Vexen saves what failed in your project, with its test result, so your next agent, even in another tool, checks it before trying again.
Install in one command ↓ · ⭐ Star on GitHub · See the evidence
npx @onurbyte/vexen setup
▶ Open the full-resolution 15-second video (MP4)
You don't need to save a conversation. Your agent saves a short note: what failed, in which file, with its test result. A later session checks it before editing the same code. If the file changes, the note steps aside.
A solved task cost 77.7% less with Vexen memory in our pilot: 4.5× cheaper.
The saving comes from more runs succeeding, not from shorter runs. In the first published pilot, Claude Code with Haiku solved 55% of tasks with relevant memory, against 10% without (11 of 20 against 2 of 20).
These are small, honest numbers: one model, synthetic tasks, notes prepared in advance. They do not show general coding improvement. Method, raw data, stale-note and control checks, and limits →
Run it inside the Git project you want Vexen to remember. You need Node.js 18 or newer (only for this installer) and Git.
On Windows PowerShell use npx.cmd @onurbyte/vexen setup. setup creates your project's memory (a local .vexen/ folder), keeps a permanent copy of Vexen on your machine, connects the coding tools it finds, then starts Vexen once and checks that it answers. It prints what it did and what it could not do. Nothing runs in the background.
Then: restart your coding tool and ask:
Use Vexen to check this project's README.md for past failures or decisions.
On a new project, “no relevant evidence” is the expected answer. When a test fails during your work, ask your agent to save the failed attempt with its file and test result. If your agent can't find Vexen, run npx @onurbyte/vexen doctor --mcp.
Full setup guide, manual steps and uninstall → · Download without Node.js →
Start a task in Claude Code. Continue in Codex or Cursor. Saved lessons stay with the project.
The installer supports eight tools; more have completed real Vexen tool calls. Setup and coverage vary. See what was tested →
- Local storage. Notes live in your project's
.vexen/folder. Database files are ignored by Git. - No Vexen cloud or telemetry. Vexen doesn't record your chats. Your coding tool's own data policies still apply.
- A source for each reminder. See the file, commit and recorded result behind a note.
- Nothing relevant? It says so. Old or unrelated evidence should not become advice for new code.
Version 1.0: the command line, the four MCP tools and the data format are stable and follow semantic versioning. Vexen gives your agent context to consider; the agent still needs to inspect the current code and test its work. What 1.0 does not claim is in the roadmap.
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