Harness as a constructor: Claude Code Mods, dsh Creator Mode
Claude Code mods
https://claude.com/blog/claude-code-mods
Works in the CLI, the Code tab of the desktop app, and (partially) VS Code. Anthropic released mods on October 1, 2026. A mod is a plugin containing JS/TS event handlers; it is no longer “agent configuration” (because who would be surprised by that now), but programming its harness. You can ask Claude Code to write a mod with hot reload in the current session — the agent edits its own interface.
Claude Code calls them on a tool call, before sending a prompt, during UI refresh, on a command, at session start. A mod lives inside the Claude Code process (from a security standpoint it gets all permissions!), not as a separate shell script, because old hooks worked from outside and therefore could not draw UI. Part of the code is open in https://github.com/anthropics/claude-code/tree/main/mods.
https://www.youtube.com/watch?v=uizaxuzgEAk
What this gives practically:
- rewrite the prompt to the model;
- block, modify, or repeat a tool call;
- approve or reject a permission request;
- cut secrets from tool output before the model sees them;
- draw a panel, a bar above the prompt, buttons, fields, select, SVG, even a game field;
- replace part of Claude Code’s own UI — the tool call line, spinner, question dialog.
Some stock Claude Code features are now mods too. For example, /diff is a mod; it can be disabled or replaced with your own. Support for AGENTS.md, sec-default, telemetry — too.
What official examples exist: Token Weather forecast of context window filling; Blast Radius will hold a dangerous command like rm -rf or force push; Replay Theater /replay shows step-by-step diffs of edits from the last turn.
Catalogs from other people — https://mods4claude.com/ and https://mods.aidojo.si/ — but one must remember about security.
DeepSeek Harness Creator Mode
https://www.deepseek.com/en/harness/
On November 2, DeepSeek publicly showed Creator Mode in DeepSeek Harness (dsh) as a public launch: “Your Harness. You Define It.” As I already wrote, Creator Mode existed in preview earlier, but without emphasizing its capabilities. In September, plugins moved to a permanent Plugin Manager, and then the item “Let Agent create a plugin” appeared.
https://www.youtube.com/watch?v=VKmUC5ukfqU
In the ad, various ways to modify functional aspects of the UI are shown: a landmarks gallery, an interactive 3D visualization of Transformer, a pixel theme for the whole app, a workspace for posters, a video editor, a floating menu for selected text, and a conversation statistics plugin. The prompts were placed here https://cdn.deepseek.com/harness/dsh-creator-mode-prompt-collection-en.html.
I wrote about Herdr yesterday. This already looks like a bridge to “software that extends itself.” Competition among harnesses is shifting from “which model is under the hood” to “how deeply I can rewrite the shell itself.”
#claudecode #deepseek #harness