Editors

fcs prints path:line:col:text when its output is not a terminal, which is the format editors’ quickfix and “go to file:line” features read.

Vim and Neovim

" one-off: results as a quickfix list
:cexpr system('fcs --format vimgrep ' . shellescape('fn main'))

" make :grep use it
set grepprg=fcs\ --format\ vimgrep\ --absolute
set grepformat=%f:%l:%c:%m

Then :grep 'fn main', :copen. --absolute maps the workspace-relative paths back to absolute ones through your configuration, so the list works from any working directory.

VS Code

Run fcs in the integrated terminal: path:line:col output is clickable. With --absolute the links resolve regardless of the folder you opened. The repository also contains a VS Code extension that talks to the server directly.

Emacs

M-x grep with fcs --format vimgrep --absolute QUERY produces a compilation buffer whose entries jump to the file and line.

Coding agents (MCP)

The server speaks the Model Context Protocol at /mcp, so Claude Code or any other MCP client can search the index, read files with line numbers and walk the import graph instead of grepping:

claude mcp add --transport http fast_code_search http://127.0.0.1:8080/mcp

Clients that only launch local commands can use fcs mcp, which relays MCP over stdio to the same endpoint:

{ "mcpServers": { "fast_code_search": { "command": "fcs", "args": ["mcp"] } } }

The tools and their arguments are listed under MCP in the API reference.

Shell

fcs -l TODO | xargs $EDITOR           # open every file containing TODO
fcs -l 'fn main' | fzf | xargs $EDITOR
fcs --json 'parse_query' | jq '.results[] | [.file_path, .line_number]'

Exit status follows grep: 0 when there were matches, 1 when none, 2 on error, so fcs -q pattern && … works in scripts.