> ## Documentation Index > Fetch the complete documentation index at: https://docs.jylhis.com/llms.txt > Use this file to discover all available pages before exploring further. # devenv integration > Run tasks, manage processes, and introspect devenv.sh environments from Emacs # devenv integration Jotain ships a native integration with [devenv](https://devenv.sh), the Nix-based developer environment tool. The library lives in `lisp/devenv.el` (standalone and reusable — no Jotain dependencies) and is wired in by `init-devenv.el`. Everything is driven through the `devenv` CLI and degrades to a clean error when the binary is not on `PATH`. devenv 2.1+ is recommended; every invocation sets `AI_AGENT=1` so devenv's TUI stays out of the machine-readable output. ## Entry point: `C-c v` `C-c v` (or `M-x devenv`) opens a transient covering the whole surface: | Key | Command | What it does | | --------------- | ----------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------- | | `t` | `devenv-task-run` | Pick a task (annotated from `devenv tasks list --json`) and run it; prefix arg selects the dependency mode (`before`/`single`/`after`/`all`) | | `s` | `devenv-script-run` | Pick a script defined in `devenv.nix` (annotated with its description) and run it | | `T` | `devenv-test` | `devenv test` (enterTest, with processes started/stopped around it) | | `b` | `devenv-build` | `devenv build`, optionally for specific attributes | | `u` / `d` | `devenv-up` / `devenv-down` | Start/stop the project's processes; `up` streams into a live buffer (or detaches, see `devenv-up-detached`); prefix arg picks a subset | | `p` | `devenv-processes` | Process dashboard (below) | | `l` | `devenv-processes-logs` | Tail one process's logs | | `i` / `/` / `:` | `devenv-info` / `devenv-search` / `devenv-eval` | Introspection: environment summary, package/option search, evaluate any config attribute to pretty-printed JSON | | `r` | `devenv-reload` | Refresh the environment (below) | | `e` | `devenv-env-global-mode` | Toggle the native environment loader (below) | | `m` | `devenv-modeline-mode` | Toggle the mode-line status segment (below) | | `a` / `x` | `devenv-allow` / `devenv-revoke` | Trust / untrust the project for auto-activation (below) | | `M` | `devenv-mcp-setup` | Register the project's MCP server with mcp.el | | `U` / `G` | `devenv-update` / `devenv-gc` | Update `devenv.lock` inputs / garbage-collect old generations | | `$` | `devenv-show-log` | Every CLI invocation is recorded in `*devenv log*` | The `-c` (`--clean`) and `-r` (`--refresh-eval-cache`) infixes apply to `devenv-test` and `devenv-build`. Long-running commands (test, build, tasks, update, gc) run in compilation buffers with Nix trace matching, so `M-g M-n` jumps to the `file.nix:LINE:COL` locations in evaluation errors. ## Process dashboard `devenv-processes` opens a tabulated view of the devenv process manager. Keys: `s` start, `k` stop, `r` restart, `l`/`RET` logs, `u` up, `d` down, `g` refresh. Data comes from `devenv processes list` (JSON when available, plain table on older devenv), fetched asynchronously so the UI never blocks. ## Environment loading and reload Environment loading stays with **envrc + direnv** (see `init-prog`): `.envrc` says `use devenv`, so every project buffer already carries the devenv shell environment buffer-locally — eglot servers, apheleia formatters, `M-x compile`, and the ghostel terminal all see devenv-provided tools with no extra configuration. After changing `devenv.nix`, run `devenv-reload` (`C-c v r`). It invalidates the library's caches, refreshes the environment through `envrc-reload-all`, and — because eglot snapshots the environment when a server starts — offers to `eglot-reconnect` every server serving the project so language servers pick up new `PATH` entries. For devenv projects **without** direnv, `devenv-env-global-mode` is an optional native loader: it fetches `devenv print-dev-env --json` asynchronously and applies it buffer-locally, envrc-style. Its predicate skips any project with a `.envrc`, so it can never double-manage a buffer envrc owns. While a fetch is in flight, `eglot-ensure` is deferred and replayed once the environment lands, so language servers never start with the wrong `PATH`. ## Auto-activation trust (`devenv allow` / `revoke`) devenv 2.1+ gates shell auto-activation behind a per-project trust database (`~/.local/share/devenv/allowed`), managed with `devenv allow` and `devenv revoke`. The integration honours the same contract: the native loader (`devenv-env-global-mode`) consults the internal `devenv hook-should-activate` check and **never evaluates an untrusted devenv.nix automatically** — exactly like the zsh/fish/nu shell hooks. `devenv-allow` (`C-c v a`) trusts the project and immediately activates the loader in its buffers; `devenv-revoke` (`C-c v x`) untrusts it and drops the native environment. On devenv versions without the trust model (\< 2.1) the loader behaves as before. Note that the direnv/envrc path has its own consent gate (`envrc-allow` → `direnv allow`), independent of devenv's database. ## Mode-line status `devenv-modeline-mode` (global, enabled by `init-devenv` at startup) adds a status segment to the mode line for buffers inside a devenv project: * **`devenv[on]`** — the buffer's environment carries the devenv shell (loaded by envrc/direnv or the native loader; detected via `DEVENV_PROFILE`). * **`devenv[off]`** — devenv project, environment not loaded. * **`devenv[!]`** — auto-activation trust denied; run `devenv-allow`. Outside devenv projects the segment is empty. `mouse-1` on the segment opens the `devenv` transient. The redisplay path is subprocess-free: trust is probed once per project in the background from `find-file-hook` and cached. ## LSP for devenv.nix devenv 2.0+ ships `devenv lsp`, a bundled nixd preconfigured with the project's devenv module options (completion, hover docs for `devenv.nix` options). `init-devenv` routes `devenv.nix` and `devenv.local.nix` buffers to it while `nil` keeps serving every other Nix file — the routing entry delegates non-devenv buffers to whatever contact was registered before it. ## MCP server for the AI stack devenv 2.0+ ships `devenv mcp`, a stdio MCP server exposing nixpkgs package search, devenv option search, and process control (list/status/logs/start/stop/restart). `devenv-mcp-setup` (`C-c v M`) registers it with [mcp.el](https://github.com/lizqwerscott/mcp.el) under a per-project name (`devenv-`); start it from `M-x mcp-hub` and run `M-x gptel-mcp-connect` to hand its tools to gptel. `devenv-mcp-remove` unregisters it. ## Customization The `devenv` customization group covers the executable name (`devenv-executable`), the quiet-mode environment (`devenv-extra-env`), global CLI flags (`devenv-global-arguments`), cache TTL and command timeout, detached `up` (`devenv-up-detached`), variables the native loader never applies (`devenv-env-ignored-variables`), and the dashboard's log line count (`devenv-processes-log-lines`).