Read a file verbatim, whole or by line range — the replacement for cat and sed -n. Omit both line numbers to read the whole file, which is how to read go.mod, a Makefile, or any JSON/YAML/TOML config that has no symbols to address. An end line past the end of the file reads to the end. A dependency's source reads as dep:/, read-only. Several ranges, in one file or many, go in one call: {"ranges": [{"path": "a.go", "lines": "280-400"}, {"path": "b.go", "lines": "700-760"}]}.

Locate declarations by name AND return their source in one call — the fused search-and-read that replaces grep -n 'func X' -A 30. Exact name matches win over substring ones. Use this instead of outline and read_range when you have not located the symbol yet. Pass queries to find several names in one call.

Add text to a file without replacing anything — a new function, a new section, an extra case. Use this for additive work instead of rewriting a surrounding symbol. With no anchor it appends to the end of the file; with one it places the text before or after that anchor, refusing if the anchor is absent or matches more than once. Several additions or edits at once belong in apply.

Replace an exact, unique string in a file. An anchor string does not move when the lines around it do, which is why follow-up edits address text rather than line numbers. Refuses when the anchor is absent or matches more than once — extend it with surrounding context to disambiguate. For several sites, use apply: atomic, one validation, no diagnostics from half-done intermediate states.

Create a brand-new file, and any missing parent directories. Refuses to overwrite an existing one — use replace_text or apply to modify existing content.

Apply several edits as one atomic unit: all land or none do. Ops: replace_text, replace_range, replace_symbol, delete_symbol, insert. Anchors are validated before anything is written, touched files are formatted, and one validation runs at the end instead of one per edit. Prefer this over several single edits when changing more than one site.

Delete a file, not a directory; fails if it does not exist. Reverting to an earlier checkpoint recreates it. To edit content use replace_text or apply.

Run a validation command on demand and wait for the verdict: kind build (default), typecheck or tests. Uses the repository's own Makefile target, npm script or cargo command when present. Waits by default and returns pass/fail directly. Every result names the command that ran; dryRun names it without running anything. In a repository with several projects, pass target to check one; with no command at the root, the answer lists the projects.

Literal or regex text search across the workspace, returning path:line matches with optional trailing context — the replacement for grep -rn. Use this for anything that is not a declaration name: struct fields, string literals, error messages, config keys, or any search needing a path filter. Use find instead when you want a declaration and its body. Pass queries to search several patterns in one call.

Run a command the repository declares, by name, and wait for the verdict: pass/fail with the decisive output. Use it instead of a shell for anything check does not cover. No name lists the declared commands. Nothing fits? declare_command it once.

Declare a named command in .arno/commands.json — a reproduction, a benchmark — to run with run_command in this and later sessions; the file is reviewed like any change. Declaring an existing name replaces it; do not redeclare one just to run it.

Rerun a failing test, a test file, or changed files' tests; waits for pass/fail and the first failure. Full suite: check kind tests.