diff --git a/README.md b/README.md
index 6171146..b030f01 100644
--- a/README.md
+++ b/README.md
@@ -91,6 +91,7 @@ See the [ubuntu-server README](ubuntu-server/README.md) for details on the Nix c
   - Shared configuration modules to eliminate duplication
   - POSIX-compliant environment setup across all shells
   - macOS login shell compatibility
+  - [inshellisense](https://github.com/microsoft/inshellisense) IDE-style inline autocomplete across all three shells (skipped in editor terminals; see [shell README](shared/.config/shell/README.md#inshellisense-ide-style-autocomplete))
 - **✏️ Editors**:
   - **Neovim (Kickstart)** - Default, mapped to `nvim`/`vim` commands
   - **Neovim (AstroVim)** - Available via `astrovim` alias
diff --git a/shared/.bashrc b/shared/.bashrc
index 49b2417..8076aa5 100644
--- a/shared/.bashrc
+++ b/shared/.bashrc
@@ -66,3 +66,9 @@ for config_file in "$HOME/.bashrc.d/"*.sh; do
 done
 
 eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv bash)"
+
+# inshellisense autocomplete — MUST be the last command (it wraps the shell in a
+# child session; keep new startup logic above this). Setup: .config/shell/README.md
+if [ -f "$HOME/.inshellisense/init/bash/init.sh" ] && ! is_integrated_terminal; then
+  . "$HOME/.inshellisense/init/bash/init.sh"
+fi
diff --git a/shared/.config/fish/README.md b/shared/.config/fish/README.md
index 8bc4bf8..cb00b4a 100644
--- a/shared/.config/fish/README.md
+++ b/shared/.config/fish/README.md
@@ -77,6 +77,7 @@ fisher update
 - **fzf** - Fuzzy finder
 - **zoxide** - Smart directory navigation
 - **fisher** - Plugin manager
+- **inshellisense** (`is`) - IDE-style inline autocomplete (optional; run `is init fish` to enable)
 
 ## Usage
 
diff --git a/shared/.config/fish/config.fish b/shared/.config/fish/config.fish
index 19a98cf..c97d897 100644
--- a/shared/.config/fish/config.fish
+++ b/shared/.config/fish/config.fish
@@ -42,3 +42,9 @@ for config_file in ~/.config/fish/config.*.fish
         source $config_file
     end
 end
+
+# inshellisense autocomplete — MUST be the last command (it wraps the shell in a
+# child session; keep new startup logic above this). Setup: .config/shell/README.md
+if status is-interactive; and test -f ~/.inshellisense/init/fish/init.fish; and not is_integrated_terminal
+    source ~/.inshellisense/init/fish/init.fish
+end
diff --git a/shared/.config/nix-darwin/README.md b/shared/.config/nix-darwin/README.md
index 77aecc6..141fd09 100644
--- a/shared/.config/nix-darwin/README.md
+++ b/shared/.config/nix-darwin/README.md
@@ -41,7 +41,7 @@ This configuration manages macOS systems declaratively using Nix, providing:
 
 ### Nix Packages (System-wide)
 - **Development**: `neovim`, `gh`, `lazygit`, `ripgrep`, `fd`
-- **Shell**: `fish`, `zellij`, `tmux`, `fzf`, `zoxide`, `atuin`
+- **Shell**: `fish`, `zellij`, `tmux`, `fzf`, `zoxide`, `atuin`, `inshellisense`
 - **Tools**: `stow`, `oh-my-posh`, `volta`, `asdf-vm`
 - **AI**: `claude-code`, `codex`
 
diff --git a/shared/.config/nix-darwin/darwin.nix b/shared/.config/nix-darwin/darwin.nix
index 81efd84..0e8ea53 100644
--- a/shared/.config/nix-darwin/darwin.nix
+++ b/shared/.config/nix-darwin/darwin.nix
@@ -42,6 +42,7 @@
     git
     gofumpt
     gum
+    inshellisense
     lazygit
     neovim
     nil
diff --git a/shared/.config/shell/README.md b/shared/.config/shell/README.md
index f619125..bfc1309 100644
--- a/shared/.config/shell/README.md
+++ b/shared/.config/shell/README.md
@@ -101,6 +101,47 @@ The `shared/` profile establishes each `.d/` directory (with a `.gitkeep`). The
 
 This complements the existing `.config/shell/` pattern (`aliases.*.sh`, `exports.*.sh`, `functions.*.sh`) for cases where profile-specific logic needs to live in the root init files rather than the shared shell config directory.
 
+## inshellisense (IDE-style autocomplete)
+
+[inshellisense](https://github.com/microsoft/inshellisense) provides fig-like,
+IDE-style inline command autocompletion for all three shells. It works by
+auto-starting a session that *wraps* the interactive shell, so the integration
+has a few non-obvious requirements that are baked into this repo:
+
+- **Must be the last command.** The source line is appended to the very end of
+  `.bashrc`, `.zshrc`, and `fish/config.fish` (after the profile `.d/` and
+  `config.*.fish` loops). inshellisense recurses into a child shell guarded by
+  the `ISTERM` env var, so anything after it in the rc file would not run in the
+  outer shell. If you add new startup logic, keep it *above* this block.
+- **Skipped in IDE/editor terminals.** The block is gated behind
+  `is_integrated_terminal`, mirroring `auto_start_tmux`, so it stays out of
+  VS Code / Neovim / Emacs / Zed terminals where a nested PTY is unwanted.
+- **No-op until provisioned.** Each shell sources
+  `~/.inshellisense/init/<shell>/init.<ext>` only if that file exists. The file
+  is created by `is init` (see below), so shells on un-provisioned machines and
+  the non-interactive CI startup-time harness are unaffected.
+
+### Installing / enabling
+
+The `is` binary is declared for macOS in
+`shared/.config/nix-darwin/darwin.nix` (`environment.systemPackages`). On
+Ubuntu / remote sandboxes install it via npm:
+
+```sh
+npm install -g @microsoft/inshellisense
+```
+
+Then generate the per-shell init files once (regenerate after upgrades):
+
+```sh
+is init                 # detects the current shell, or pass bash|zsh|fish
+```
+
+`is init` writes `~/.inshellisense/init/<shell>/init.<ext>`, which the rc files
+already source. No changes to the rc files themselves are needed — do **not**
+run `is init <shell> >> ~/.<shell>rc` (the upstream instructions), as that would
+duplicate the source line this repo already manages. Run `is doctor` to verify.
+
 ## Benefits
 
 1. **No duplication**: Shared configuration is centralized
diff --git a/shared/.zshrc b/shared/.zshrc
index 3098534..245b1a6 100644
--- a/shared/.zshrc
+++ b/shared/.zshrc
@@ -204,3 +204,9 @@ for config_file in "$HOME/.zshrc.d/"*.sh; do
     . "$config_file"
   fi
 done
+
+# inshellisense autocomplete — MUST be the last command (it wraps the shell in a
+# child session; keep new startup logic above this). Setup: .config/shell/README.md
+if [[ -f "$HOME/.inshellisense/init/zsh/init.zsh" ]] && ! is_integrated_terminal; then
+  . "$HOME/.inshellisense/init/zsh/init.zsh"
+fi