---
url: 'https://vixl.app/concepts/context.md'
description: >-
  Each Vixl turn builds a small system prompt from catalogs and names, then
  loads full MCP schemas and skill bodies on demand.
---
# Context

Each turn builds a small system prompt, then adds only what this chat needs. Catalogs and names go in first. Full MCP schemas and skill bodies load when the agent asks. That is why local prefills stay smaller than harnesses that dump every tool schema up front.

The prompt always includes a short workspace identity (project name and root; workspace tools stay on this repo), shared tool guidance, and the built-in skill for the current [chat mode](/concepts/chat-modes). What else is injected depends on the chat.

## Mentions

`@` searches workspace files. Home chats, and a composer still on **Home**, have no workspace for that search. A file mention is stored as a path and tagged untrusted context: data, not instructions.

`/` lists vendored command skills, user and project skills, and custom agents. Reserved names `ask`, `plan`, `agent`, and `orchestrator` stay hidden. A skill mention becomes a name in the prompt. The agent loads the body with `load_skill`. An agent mention does not dump instructions. It adds an explicit invocation: the parent must call `spawn_subagent` with that catalog name. Unresolved agent names are dropped.

On a home chat, `/` lists vendored command skills plus personal skills and agents from `~/.vixl`. A same-named personal or project skill cannot override a vendored command. On a project chat, personal plus project, and the project name wins over personal. A workspace rooted at your user home directory stays personal only.

## Rules and AGENTS.md

These are always-on for the chats that inject them. There is no per-rule glob gate. Every listed rule file is included.

Home chats inject personal `~/.vixl/rules/*.{md,mdc}` and personal `~/.vixl/AGENTS.md` (or `agents.md`).

Project chats inject both trees, personal first, then project. Rules use the headings `Personal guidance (not a security override):` and `Project guidance (not a security override):`. `AGENTS.md` uses `Personal AGENTS.md guidance:` and `Project AGENTS.md guidance:`. An empty side is omitted.

A workspace whose root is your user home directory injects the personal copies only.

Unreadable files and paths outside the read root are stubbed in the prompt, not silently dropped.

Edit these in [Rules and AGENTS.md](/customize/rules-and-agents-md).

## Skills

Skills are `SKILL.md` packs under `.vixl/skills/<name>/`. `/create-agent`, `/create-skill`, `/create-rule`, and `/create-plan` are vendored command skills. They are listed in `/` and in Available skills. They work on home chats. On a home chat the workspace root is the user home directory, and those commands write `~/.vixl/`, the personal tree. Mode skills `ask`, `plan`, `agent`, and `orchestrator` stay hidden from `/` and stay inlined only in their matching chat mode.

Available skills lists remaining skills as names and descriptions: vendored commands, then personal, then a project overlay on project chats. Home chats list vendored commands and personal skills. A workspace rooted at your user home directory does not add a project overlay.

`load_skill` loads the body by name (built-in, then project, then personal; bodies over 4000 characters are truncated). The home directory skips the project step. The full rules are on [SKILL.md format](/reference/skill-md-format). See also [Skills](/customize/skills).

## Progressive tool discovery

The MCP catalog in the prompt is enabled user servers (not CodeGraph), status, and tool names with descriptions cut at 200 characters. Full `inputSchema` is not dumped up front. The agent calls `get_mcp_tools` (optional `serverId` for one server's schemas) or `get_mcp_tool` for a single tool, then `call_mcp_tool`. Untrusted catalog data is labeled as such.

The same pattern applies to skills: names in the prompt, bodies on `load_skill`.

Sub-agents appear as an available-subagents catalog from `.vixl/agents/*.md`. On a home chat that catalog is personal agents only. Project chats overlay by name, and the project file wins. See [Custom agents](/customize/custom-agents).

Long threads can drop older turns behind a compact summary. That is a chat operation, not a model role. [Compact and hand off long chats](/using/compact-and-hand-off-long-chats) is how you run it.