Direct Tools

session.tool(name, args) (and the typed helpers like glob, grep, readFile) run a host tool directly, with no model call in the loop. Use them for tests, migrations, and host-driven workflows where you want deterministic results instead of an agent turn.

Direct calls are host control-plane calls. Apply your own product authorization before invoking them; permissionPolicy gates model-selected tool calls inside an agent turn, not whether your application code is allowed to call an SDK helper.

Rust

Node.js

Python

Rust

use a3s_code_core::Agent;
use serde_json::{json, Value};
use std::collections::HashSet;

#[tokio::main]
async fn main() -> a3s_code_core::Result<()> {
    let agent = Agent::new("agent.acl").await?;
    let session = agent.session_builder(".").build().await?;

    let allowed = HashSet::from(["glob", "grep", "read", "generate_object"]);
    let check = |name: &str| -> a3s_code_core::Result<()> {
        allowed
            .contains(name)
            .then_some(())
            .ok_or_else(|| {
                a3s_code_core::CodeError::Security(format!(
                    "direct tool not allowed here: {name}"
                ))
            })
    };

    check("glob")?;
    let files = session.glob("**/*.rs").await?;
    println!("glob found {} Rust files", files.len());

    check("grep")?;
    let matches = session.grep("Agent::new").await?;
    println!("grep found {} matching lines", matches.lines().count());

    check("read")?;
    let readme = session.read_file("README.md").await?;
    println!("README is {} bytes", readme.len());

    let raw = session
        .tool("read", json!({ "file_path": "Cargo.toml" }))
        .await?;
    println!("Cargo.toml via tool(): {} bytes", raw.output.len());
    println!("session exposes {} tools", session.tool_definitions().len());

    check("generate_object")?;
    let structured = session
        .tool(
            "generate_object",
            json!({
                "schema": {
                    "type": "object",
                    "required": ["count", "language"],
                    "properties": {
                        "count": { "type": "integer" },
                        "language": { "type": "string" }
                    }
                },
                "prompt": "How many Rust files are in this project?",
                "schema_name": "file_stats"
            }),
        )
        .await?;
    if structured.exit_code != 0 {
        return Err(a3s_code_core::CodeError::Tool {
            tool: "generate_object".into(),
            message: structured.output,
        });
    }
    let generated: Value = serde_json::from_str(&structured.output)?;
    println!("structured output: {}", generated["object"]);

    session.close().await;
    agent.close().await;
    Ok(())
}

TypeScript

import { Agent } from '@a3s-lab/code';

const agent = await Agent.create('agent.acl');
const session = agent.session('.');

const allowedDirectTools = new Set(['glob', 'grep', 'read', 'generate_object']);
function assertDirectToolAllowed(name: string) {
  if (!allowedDirectTools.has(name)) {
    throw new Error(`direct tool not allowed here: ${name}`);
  }
}

// Glob: list files by pattern
assertDirectToolAllowed('glob');
const files = await session.glob('**/*.ts');
console.log(`glob found ${files.length} TypeScript files`);

// Grep: search file contents
assertDirectToolAllowed('grep');
const matches = await session.grep('Agent.create');
const matchCount = matches.split('\n').filter(Boolean).length;
console.log(`grep found ${matchCount} matching lines`);

// Read a file
assertDirectToolAllowed('read');
const readme = await session.readFile('README.md');
console.log(`README is ${readme.length} bytes`);

// Direct tool call by name
assertDirectToolAllowed('read');
const raw = await session.tool('read', { file_path: 'package.json' });
console.log(`package.json via tool(): ${raw.output.length} bytes`);

// Inspect available tool schemas
const schemas = session.toolDefinitions();
console.log(`session exposes ${schemas.length} tools`);

// Structured output: generate a schema-validated JSON object
assertDirectToolAllowed('generate_object');
const structured = await session.tool('generate_object', {
  schema: {
    type: 'object',
    required: ['count', 'language'],
    properties: {
      count: { type: 'integer' },
      language: { type: 'string' },
    },
  },
  prompt: 'How many TypeScript files are in this project?',
  schema_name: 'file_stats',
});
if (structured.exitCode !== 0) {
  throw new Error(structured.output);
}
console.log('structured output:', JSON.parse(structured.output).object);

session.close();

Python

import json

from a3s_code import Agent

agent = Agent.create("agent.acl")
session = agent.session('.')

ALLOWED_DIRECT_TOOLS = {'glob', 'grep', 'read', 'generate_object'}


def assert_direct_tool_allowed(name: str) -> None:
    if name not in ALLOWED_DIRECT_TOOLS:
        raise RuntimeError(f'direct tool not allowed here: {name}')

# Glob: list files by pattern
assert_direct_tool_allowed('glob')
files = session.glob('**/*.py')
print(f'glob found {len(files)} Python files')

# Grep: search file contents
assert_direct_tool_allowed('grep')
matches = session.grep('Agent.create')
match_count = len([line for line in matches.splitlines() if line])
print(f'grep found {match_count} matching lines')

# Read a file
assert_direct_tool_allowed('read')
readme = session.read_file('README.md')
print(f'README is {len(readme)} bytes')

# Direct tool call by name
assert_direct_tool_allowed('read')
raw = session.tool('read', {'file_path': 'pyproject.toml'})
print(f'pyproject.toml via tool(): {len(raw.output)} bytes')

# Inspect available tool schemas
schemas = session.tool_definitions()
print(f'session exposes {len(schemas)} tools')

# Structured output: generate a schema-validated JSON object
assert_direct_tool_allowed('generate_object')
structured = session.tool('generate_object', {
    'schema': {
        'type': 'object',
        'required': ['count', 'language'],
        'properties': {
            'count': {'type': 'integer'},
            'language': {'type': 'string'},
        },
    },
    'prompt': 'How many Python files are in this project?',
    'schema_name': 'file_stats',
})
if structured.exit_code != 0:
    raise RuntimeError(structured.output)
print('structured output:', json.loads(structured.output)['object'])

session.close()

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"strings"

	code "github.com/A3S-Lab/Code/sdk/go/v6"
)

func must[T any](value T, err error) T {
	if err != nil {
		log.Fatal(err)
	}
	return value
}

func main() {
	ctx := context.Background()
	agent := must(code.Create(ctx, "agent.acl"))
	defer agent.Close(context.Background())
	session := must(agent.Session(ctx, ".", nil))
	defer session.Close(context.Background())

	files := must(session.Glob(ctx, "**/*.go"))
	fmt.Printf("glob found %d Go files\n", len(files))

	matches := must(session.Grep(ctx, "code.Create"))
	fmt.Printf("grep found %d matching lines\n", len(strings.Split(matches, "\n")))

	readme := must(session.ReadFile(ctx, "README.md", nil))
	fmt.Printf("README is %d bytes\n", len(readme))

	raw := must(session.Tool(ctx, "read", map[string]any{
		"file_path": "go.mod",
	}))
	fmt.Printf("go.mod via Tool(): %d bytes\n", len(raw.Output))

	schemas := must(session.ToolDefinitions(ctx))
	fmt.Printf("session exposes %d tools\n", len(schemas))

	structured := must(session.Tool(ctx, "generate_object", map[string]any{
		"schema": map[string]any{
			"type":     "object",
			"required": []string{"count", "language"},
			"properties": map[string]any{
				"count":    map[string]any{"type": "integer"},
				"language": map[string]any{"type": "string"},
			},
		},
		"prompt":      "How many Go files are in this project?",
		"schema_name": "file_stats",
	}))
	if structured.ExitCode != 0 {
		log.Fatal(structured.Output)
	}
	var generated struct {
		Object map[string]any `json:"object"`
	}
	if err := json.Unmarshal([]byte(structured.Output), &generated); err != nil {
		log.Fatal(err)
	}
	fmt.Println("structured output:", generated.Object)
}

Direct tools execute under the session workspace and should be treated as privileged host operations. Most calls (read, glob, grep) are purely deterministic; generate_object is the exception — it still calls the model to fill a schema-validated JSON object, but you drive it explicitly rather than through a free-form agent turn.

A runnable version ships at sdk/node/examples/basic/test_generate_object.ts (Python: sdk/python/examples/test_generate_object.py). The Go direct-tool contract is covered by sdk/go/session_test.go.

#Direct Tools

Direct Tools