Built-in agent tools

These are the tools the built-in agent runtime registers directly, as opposed to the MCP tools it bridges in. They are not on the MCP registry: an external MCP client will not see them, because each one is bound to a live server-side resource — a language server process, a debug adapter, an interpreter — that belongs to one run.

Every tool here is registered conditionally. A tool whose resource cannot exist on this host is not advertised at all, rather than advertised and failing on call.

Approval tiers

Each tool declares a tier, and the tier decides which surfaces see it — not merely whether it prompts. Plan mode and read-only subagents are capped at read, so a write- or exec-tier tool is absent from their schema entirely.

Tier	Meaning	Tools here
read	No side effects	lsp, ast_grep, ask_user, the five vibe_*
write	Changes files	lsp_rename, ast_edit, resolve
exec	Starts or controls a process	debug, eval

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lsp — language-server queries

Registered when a language server is detected for the checkout. Detection is an intersection: a root marker must exist and the server binary must resolve. Either one alone means the tool is not offered.

Positions are addressed by line plus a symbol substring, never by column. A model asked for a column guesses, and a wrong guess resolves to a different symbol on the same line — an answer that looks right and is about something else. Omitting symbol on a navigation action is an error, not a first-column guess.

Action	Arguments	Returns
diagnostics	file (or "*")	Errors and warnings; "*" runs the project checker instead
definition	file, line, symbol	Where the symbol is declared
type_definition	file, line, symbol	Where its type is declared
implementation	file, line, symbol	Concrete implementations
references	file, line, symbol	Every use, capped at 50
hover	file, line, symbol	Signature and doc comment
symbols	query	Workspace symbol search, capped at 200
code_actions	file, line	Quick fixes the server offers
status	—	Which servers are running, and for which roots
reload	—	Restarts the server for this root

Diagnostics on write

The payoff is not the tool. write, edit and apply_patch are wrapped: after the write the file is synced and saved through the language server, and only newly introduced diagnostics are folded into the tool result. An agent finds out it broke the build at the moment it broke it, without having to remember to ask.

Already-reported diagnostics are suppressed by a per-run ledger keyed on severity, code and message — position deliberately excluded, so a diagnostic that merely moved down four lines is not re-reported as new.

lsp_rename — project-wide rename

A separate, write-tier tool for exactly one reason: the tier decides visibility. Folding rename into lsp would either hand a read-only explorer the ability to rewrite the repo, or put every hover behind an approval prompt.

Argument	Meaning
file	Where the symbol is
line	1-indexed line
symbol	Substring identifying it on that line
new_name	What to call it

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ast_grep — structural search

Finds code by shape rather than by text. $NAME matches any node, $$$NAME matches a run of siblings, and $_ is a wildcard that binds nothing.

The property that makes it a matcher rather than a regex with extra steps: a metavariable repeated in one pattern must capture the same text.

ast_grep(pattern: "if ($X != null) $X.dispose()", language: "dart")

matches a guard that disposes what it tested, and does not match one that disposes something else.

Argument	Meaning
pattern	A code fragment with metavariables
path	File or directory to search; defaults to the whole workspace
language	dart, javascript, typescript, tsx, php. Inferred when path names a file
max_results	Default 50

The pattern is parsed by the same grammar as the file

So dispose(x) matches the call however it is spaced, wrapped or commented — and never matches the same characters inside a string literal or a comment.

A fragment is parsed in a scaffold, not bare

dispose(x) parsed at Dart’s top level is a valid function signature. The pattern compiler tries a ladder of contexts (statement, expression, class member, declaration) and uses the first that accepts the fragment. A pattern no context accepts is reported as unparseable rather than searched for and silently not found.

ast_edit — structural rewrite, staged

Same matching, plus a rewrite template with the metavariables substituted back in. Nothing is written. The change is staged and the result names an edit_id.

ast_edit(pattern: "dispose($X)", rewrite: "$X.dispose()", language: "dart")
→ (proposed) 12 replacements in 4 files … call resolve with edit_id "edit_1"

Argument	Meaning
pattern	What to match
rewrite	What to put there, with $NAME substituted
path	Scope; defaults to the whole workspace
language	Language id

resolve — commit or discard a staged change

Argument	Meaning
edit_id	From the (proposed) result
action	accept or discard

Every file is compared against the content captured at staging time, and any mismatch refuses the whole change. A partly-applied structural rewrite leaves a tree that compiles under neither the old shape nor the new one.

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debug — drive a debugger

Registered when a debug adapter is detected for the checkout, by the same intersection rule as the language server. exec tier; not parallel-safe (a session is state across calls, so continue overtaking stack would read a frame that has already moved).

One session per conversation, with a hard TTL. A second launch is refused rather than silently replacing the first.

Op	Arguments	Notes
adapters	—	Which adapters are usable here, and why not
status	—	Whether a session is running, and where it stopped
breakpoints	file, lines[]	Empty lines clears the file. May be set before launching
launch	program, args[]	Starts the program stopped at your breakpoints
attach	port	Connects to an already-running debuggee
continue	thread_id?	Runs until the next stop
pause	thread_id?	Stops it where it is
step_over / step_in / step_out	thread_id?	Moves one step
threads	—	Thread ids and names
stack	thread_id?	Frames, capped at 30
scopes	frame_id	Scopes on a frame, each with a reference
variables	reference	Children, capped at 50, values capped at 400 chars
evaluate	expression, frame_id?	Evaluated in the frame’s own scope
output	—	The debuggee’s stdout/stderr, bounded
terminate	—	Ends the session and kills the adapter

Adapters

Id	Command	Root markers
dart	dart debug_adapter	pubspec.yaml
debugpy	python3 -m debugpy.adapter	pyproject.toml, setup.py, requirements.txt
lldb	lldb-dap	Cargo.toml, CMakeLists.txt
delve	dlv dap	go.mod

debugpy prefers a project-local .venv/bin over $PATH: a $PATH python is a different environment, and attaching from the wrong one fails in a way that reads as broken code.

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eval — persistent interpreters

A Python or JavaScript cell whose variables, imports and loaded data survive between calls. exec tier; not parallel-safe.

Argument	Meaning
code	The cell
language	python (default) or javascript
reset	Discard the interpreter and start clean first

• The last expression is echoed the way a notebook does.
• display() works, a pandas frame renders as a table, and a matplotlib figure comes back as an image the transcript shows.
• The IPython idioms people reflexively type — %pip, %cd, !cmd, %%bash, %%timeit — are rewritten into plain code. %pip also evicts sys.modules, so the next import sees what was just installed.

Calling your own tools from inside a cell

contents = tool("read", {"path": "lib/auth.dart"})

The bridge re-enters the harness tool registry, so guardrails, approval and every wrapper apply exactly as they do to a model-issued call. It rides the kernel’s own pipe rather than a loopback socket: no port, no secret, no egress rule.

The cell’s timeout is an inactivity budget and it is suspended while a bridged call is outstanding, so a cell that fans out to subagents is not killed mid-fanout.

Where the kernel runs

In the conversation’s enclosure when it has one, on the host otherwise. It does not boot an enclosure to get there — the same rule that stops a rig tab auto-starting.

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ask_user — ask the human a question

read tier. Renders a structured question in the conversation and blocks the run until someone answers.

Argument	Meaning
question	What to ask
options[]	Choices, each {label, description?}
allow_free_text	Whether a typed answer is accepted
multi_select	Whether several options may be chosen

Registered only when both a question port and a target space exist. Without a human attached the call fails rather than blocking forever — the same fail-closed posture a guardrail prompt takes with no approver connected.

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vibe_* — directing background workers

Registered only while vibe mode is on. All five are read tier: the gate belongs on the worker’s tools, where the edit actually happens.

Tool	Arguments	Notes
vibe_spawn	brief, label, tier?	Returns immediately; the worker runs on
vibe_send	worker_id, message	Appends to the brief and re-runs
vibe_wait	worker_id, timeout_seconds?	Blocks until it settles
vibe_kill	worker_id	Stops it
vibe_list	—	Tier, status, elapsed and last result

tier is fast (mechanical work with a clear specification) or good (design, judgment, or reviewing a fast worker’s output).