258| `CLAUDE_CODE_SCROLL_SPEED` | Set the mouse wheel scroll multiplier in [fullscreen rendering](/en/fullscreen#mouse-wheel-scrolling). Accepts values from 1 to 20, and fractional values below 1 such as `0.5` to slow accelerated trackpad and wheel scrolling in terminals that already amplify wheel events. Set to `3` to match `vim` if your terminal sends one wheel event per notch without amplification. Ignored in the JetBrains IDE terminal, where Claude Code uses its own scroll handling |258| `CLAUDE_CODE_SCROLL_SPEED` | Set the mouse wheel scroll multiplier in [fullscreen rendering](/en/fullscreen#mouse-wheel-scrolling). Accepts values from 1 to 20, and fractional values below 1 such as `0.5` to slow accelerated trackpad and wheel scrolling in terminals that already amplify wheel events. Set to `3` to match `vim` if your terminal sends one wheel event per notch without amplification. Ignored in the JetBrains IDE terminal, where Claude Code uses its own scroll handling |
259| `CLAUDE_CODE_SESSIONEND_HOOKS_TIMEOUT_MS` | Override the time budget in milliseconds for [SessionEnd](/en/hooks#sessionend) hooks. Applies to session exit, `/clear`, and switching sessions via interactive `/resume`. By default the budget is 1.5 seconds, automatically raised to the highest per-hook `timeout` configured in settings files, up to 60 seconds. Timeouts on plugin-provided hooks do not raise the budget |259| `CLAUDE_CODE_SESSIONEND_HOOKS_TIMEOUT_MS` | Override the time budget in milliseconds for [SessionEnd](/en/hooks#sessionend) hooks. Applies to session exit, `/clear`, and switching sessions via interactive `/resume`. By default the budget is 1.5 seconds, automatically raised to the highest per-hook `timeout` configured in settings files, up to 60 seconds. Timeouts on plugin-provided hooks do not raise the budget |
260| `CLAUDE_CODE_SESSION_ID` | Set automatically to the current session ID in Bash and PowerShell tool subprocesses, [hook command](/en/hooks) subprocesses, and stdio [MCP server](/en/mcp) subprocesses. For Bash, PowerShell, and hooks this matches the `session_id` field in the hook JSON input and is updated on `/clear`. An MCP server subprocess retains the ID it was spawned with. On `--resume <session-id>` it receives the resumed ID, matching hooks and Bash. On `--continue` or `--resume` without an explicit ID it may receive the initial startup ID instead. Use to correlate scripts and external tools with the Claude Code session that launched them |260| `CLAUDE_CODE_SESSION_ID` | Set automatically to the current session ID in Bash and PowerShell tool subprocesses, [hook command](/en/hooks) subprocesses, and stdio [MCP server](/en/mcp) subprocesses. For Bash, PowerShell, and hooks this matches the `session_id` field in the hook JSON input and is updated on `/clear`. An MCP server subprocess retains the ID it was spawned with. On `--resume <session-id>` it receives the resumed ID, matching hooks and Bash. On `--continue` or `--resume` without an explicit ID it may receive the initial startup ID instead. Use to correlate scripts and external tools with the Claude Code session that launched them |
261| `CLAUDE_CODE_SHELL` | Override automatic shell detection. Useful when your login shell differs from your preferred working shell (for example, `bash` vs `zsh`) |261| `CLAUDE_CODE_SHELL` | Set the shell Claude Code uses to run Bash tool commands. Accepts a path to a `bash` or `zsh` binary, for example `/opt/homebrew/bin/bash`. Other shells such as `fish` are not supported. If the value is not a working `bash` or `zsh` path, Claude Code ignores it and falls back to auto-detection. Auto-detection uses your `$SHELL` when it points to `bash` or `zsh`, otherwise it picks the first working `zsh` then `bash` found on your `PATH` and standard install locations |
262| `CLAUDE_CODE_SHELL_PREFIX` | Command prefix that wraps shell commands Claude Code spawns: Bash tool calls, [hook](/en/hooks) commands, [status line](/en/statusline) commands, and stdio [MCP server](/en/mcp) startup commands. PowerShell hooks and exec-form hooks run without the prefix. Useful for logging or auditing. Setting a bare executable path such as `/path/to/logger.sh` runs each command as `/path/to/logger.sh '<command>'`. The wrapper receives the command line as a single shell-quoted argument in `$1`, so the wrapper must re-evaluate `$1` with a shell, for example `exec bash -c "$1"`. Treating `$1` as a bare executable path breaks stdio MCP servers that pass arguments such as `npx -y <package>`. For Bash tool calls, `$1` contains the full shell invocation Claude Code assembles, including environment setup, not only the command Claude ran |262| `CLAUDE_CODE_SHELL_PREFIX` | Command prefix that wraps shell commands Claude Code spawns: Bash tool calls, [hook](/en/hooks) commands, [status line](/en/statusline) commands, and stdio [MCP server](/en/mcp) startup commands. PowerShell hooks and exec-form hooks run without the prefix. Useful for logging or auditing. Setting a bare executable path such as `/path/to/logger.sh` runs each command as `/path/to/logger.sh '<command>'`. The wrapper receives the command line as a single shell-quoted argument in `$1`, so the wrapper must re-evaluate `$1` with a shell, for example `exec bash -c "$1"`. Treating `$1` as a bare executable path breaks stdio MCP servers that pass arguments such as `npx -y <package>`. For Bash tool calls, `$1` contains the full shell invocation Claude Code assembles, including environment setup, not only the command Claude ran |
263| `CLAUDE_CODE_SIMPLE` | Set to `1` to run with a minimal system prompt and only the Bash, file read, and file edit tools. MCP tools from `--mcp-config` are still available. Disables auto-discovery of hooks, skills, plugins, MCP servers, auto memory, and CLAUDE.md. OAuth tokens and keychain credentials are not read, so Anthropic authentication must come from `ANTHROPIC_API_KEY` or an `apiKeyHelper` in `--settings`. Equivalent to passing [`--bare`](/en/headless#start-faster-with-bare-mode) |263| `CLAUDE_CODE_SIMPLE` | Set to `1` to run with a minimal system prompt and only the Bash, file read, and file edit tools. MCP tools from `--mcp-config` are still available. Disables auto-discovery of hooks, skills, plugins, MCP servers, auto memory, and CLAUDE.md. OAuth tokens and keychain credentials are not read, so Anthropic authentication must come from `ANTHROPIC_API_KEY` or an `apiKeyHelper` in `--settings`. Equivalent to passing [`--bare`](/en/headless#start-faster-with-bare-mode) |
264| `CLAUDE_CODE_SIMPLE_SYSTEM_PROMPT` | Set to `1` to use a shorter system prompt and abbreviated tool descriptions on any model. Set to `0`, `false`, `no`, or `off` to opt out even on models where the experiment or server configuration would otherwise enable it. The full tool set, hooks, MCP servers, and CLAUDE.md discovery remain enabled |264| `CLAUDE_CODE_SIMPLE_SYSTEM_PROMPT` | Set to `1` to use a shorter system prompt and abbreviated tool descriptions on any model. Set to `0`, `false`, `no`, or `off` to opt out even on models where the experiment or server configuration would otherwise enable it. The full tool set, hooks, MCP servers, and CLAUDE.md discovery remain enabled |
