Tools

Tool	Approval	Notes
read_file	automatic	Numbered lines, offset/limit for paging; a PNG, JPEG, GIF or WebP comes back as a picture the model can look at
glob	automatic	Newest first; *.go matches at any depth
grep	automatic	ripgrep when present, pure Go otherwise, identical output either way
edit_file	prompts	Requires a prior read; refuses ambiguous matches; returns a diff and any diagnostics
write_file	prompts	Whole files only; separate from edit_file so the metrics stay honest
bash	prompts	Own process group, killed whole on timeout; output capped head and tail. background: true returns a handle instead of waiting
process_output	never	New output from a background process since you last asked, and whether it is still running
process_kill	never	Stops a background process and its children; everything is killed when the session ends anyway
todo_write	never	The working plan for a multi-step task; the whole list is sent each time
context_status	never	How full the window is, how many turns and what they cost
ask_user	never	Puts a multiple-choice question to you and waits — see questions
web_search	prompts	Only with web_search: custom; runs ddgs on this machine
web_fetch	prompts	With either web search mode; refuses private and loopback addresses
mcp__<server>__<tool>	prompts	One per tool of each MCP server in the config

Diagnostics

The agent writes a file and finds out it broke the build three tool calls later, if at all. The cheapest fix is to put the compiler's own opinion in the result the model is already reading:

⏺ EditFile(path=internal/agent/loop.go)
  ⎿ 4 additions, 1 removal
    …

    diagnostics (gopls): 2 problems
      loop.go:14:2: undefined: fmt.Printl
      loop.go:19:6: declared and not used: n

After a successful edit_file or write_file, the changed file goes to whatever this machine already has for its language — gopls, pyright-langserver, typescript-language-server or rust-analyzer if one is on PATH, and otherwise the compiler or linter: go build and go vet, ruff or pyflakes, eslint or tsc, shellcheck. Nothing is installed and nothing leaves the machine.

A clean file adds nothing at all. Silence is the good news, and a "0 problems" line on every edit would be a paragraph of tokens per edit saying that nothing happened. Ten problems are reported and the rest counted, and a diagnostic about a neighbouring file — the helper you have just renamed out from under — is kept and labelled, because that is the one the agent has no other way to learn about.

Language servers are started once and kept warm between edits, keyed by the workspace around the file rather than by the working root, so /worktree does not strand a warm gopls behind it. A check that has not finished in two seconds is abandoned rather than waited for: a tool call that hangs because a language server is confused is far worse than one that reports nothing. Every other way this can go wrong lands in the same place — a server that will not start, that dies mid-session, that answers with garbage, or one on PATH that turns out to be a broken shim — and the answer is always no diagnostics and a fall through to the linter, never a hung tool call. A server that fails to start is put on a five-minute cooldown rather than retried on every edit.

It is on by default, which is the one setting here that leans that way: it runs a tool you already have, against a file you already told the agent to write, and nothing it reads goes anywhere. "diagnostics": "off" in the config, the /settings row, or -no-diagnostics for a single run turns it off.