System tools reference¶

This page lists every system tool implemented in MAS-Lab. A system tool is a tool the runtime provides to the model, as opposed to a tool you declare in a tool server. 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-library-standard`	declared only	—
`inform_user`	`mas-library-standard`	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.

Example: declare a system tool on an agent.

spec:
  tools:
    - kind: system
      name: request_human_input
      params:
        timeout: 300

Skill tools¶

`activate_skill`¶

Loads the full SKILL.md body of a catalog skill. The returned body has no frontmatter. 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 HITL (human in the loop) side channel resolves it. The channel is an HITLContract. If none is provided, the HITL resolver registry is used.

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.library.standard.plugins.system_tools.request_human_input.RequestHumanInputTool.

`inform_user`¶

Sends a non-blocking progress update. The call returns at once 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

A UserIOContract delivers the update. If none is provided, the HITL resolver registry does.

Implementation: mas.library.standard.plugins.system_tools.inform_user.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. mas-ctl tears the instance down after the turn. See Spawned subagents and Tutorial 12.

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

System tools reference¶

Skill tools¶

activate_skill¶

list_skill_files¶

read_skill_file¶

run_skill_script¶

User-communication tools¶

request_human_input¶

inform_user¶