System tools reference

This page lists every system tool implemented in MAS-Lab. For the rules that enable each tool, see System tools.

Tool	Package	Enablement	Declaration aliases
activate_skill	mas-library-skills	implicit (spec.skills) or declared	skill-access, skill_access
list_skill_files	mas-library-skills	with activate_skill	—
read_skill_file	mas-library-skills	with activate_skill	—
run_skill_script	mas-library-skills	implicit (skill scripts/, auto_inject) or declared	run-skill-script
request_human_input	mas-runtime	declared only	—
inform_user	mas-runtime	declared only	—
create_subagent	mas-library-standard	declared only	spawn_subagent

The skill tools require mas-library-skills. Without it, declaring one fails with an unknown system tool error.

Skill tools

activate_skill

Loads the full SKILL.md body of a catalog skill. Frontmatter is removed from the returned body, and bundled resources are listed.

Argument	Type	Required	Notes
name	string	yes	Constrained to registered skill names. Names already activated are dropped from the enum.

Implementation: mas.library.skills.plugins.sk_tools.SkillToolsPlugin.

list_skill_files

Lists the files in a skill directory, such as references, scripts, and assets.

Argument	Type	Required
skill	string	yes

read_skill_file

Reads one file from a skill directory.

Argument	Type	Required	Notes
skill	string	yes
path	string	yes	Relative to the skill directory, such as references/rules.md

run_skill_script

Runs a script from the skill's scripts/ directory with resource limits. Returns stdout, stderr, and the exit code.

Argument	Type	Required	Notes
skill	string	yes
script	string	yes	Plain filename, no path
args	string[]	no	Positional arguments
timeout	integer	no	Seconds; default 30, maximum 120
env	object	no	Extra variables. Loader-control variables such as PATH and LD_PRELOAD are rejected.
stdin	string	no	Text sent to the script's standard input

Implementation: mas.library.skills.plugins.sk_shell.RunSkillScriptPlugin.

User-communication tools

request_human_input

Asks the user a question and blocks the agent's turn until the question is resolved through the HITL side channel. The channel is an HITLContract, or the HITL resolver registry if no contract is provided.

Argument	Type	Required	Notes
question	string	yes	Up to max_question_length characters
question_type	string	no	CONFIRM (default), FREE_FORM, MULTIPLE_CHOICE, MULTI_SELECT, FORM
choices	string[]	no	Options for MULTIPLE_CHOICE and MULTI_SELECT questions
context_data	object	no	Data displayed with the question
timeout	number	no	Overrides the manifest default for one call

Manifest params	Default	Notes
timeout	none (wait indefinitely)	Default timeout for each call, in seconds
auto_resolve_decision	approve	Answer used when the host runs unattended (mas-ctl run-mas with auto-HITL, benchmarks).
max_question_length	20000	Also sets the schema advertised to the model

Implementation: mas.runtime.system_tools.RequestHumanInputTool.

inform_user

Sends a non-blocking progress update. The call returns immediately and the agent continues.

Argument	Type	Required	Notes
message	string	yes	Up to max_message_length characters
user_name	string	no
involved_agents	string[]	no
metadata	object	no

Manifest params	Default	Notes
max_message_length	20000	Also sets the schema advertised to the model

The update is delivered through a UserIOContract or, if none is provided, the HITL resolver registry.

Implementation: mas.runtime.system_tools.InformUserTool.

Orchestration tools

create_subagent

Creates a bounded subagent from a declared template, runs it for one turn, and returns the child's text. Alias advertised to the model: spawn_subagent. Declare either name on the parent manifest.

Argument	Type	Required	Notes
template	string	yes	Enum of params.templates[].id
task	string	yes	Task for the child; not a new manifest

Manifest params	Default	Notes
templates	(required)	{id, ref, description} rows; ref is a local Agent manifest
max_spawns	8	Session-wide ledger
max_depth	3	Nested create/spawn depth

The child cannot invent tools or templates. Ctl tears the instance down after the turn. See Spawned subagents and Tutorial 7.

Implementation: mas.library.standard.plugins.system_tools.spawn_subagent.SpawnSubagentTool (advertise) plus mas.library.standard.plugins.engine_tools.subagent_spawner.SubagentSpawner (run).