BuiltinTools.Select

C# · package Toolnexus · SPEC §4A · BuiltinTools.cs

public static List<ITool> Select(object? cfg)

Resolves the active built-in tools for a config value. cfg is the same shape MCP servers use for isEnabled-style precedence:

• null — default on: all ten built-ins.
• bool — the whole source on (true) or off (false).
• IDictionary<string, object?> with disabled/enabled/tools keys — disabled: true wins over everything; else enabled: false turns the whole source off; otherwise a tools name→bool map drops individual tools from the all-on baseline (false-mapped names are dropped, true/absent stay on, unknown names are ignored).

Whole-source-off returns an empty list. Otherwise Select calls BuiltinTools.Create and filters it.

When to use it

Wiring Toolkit.Options.Builtins — this is what the toolkit calls internally to decide which built-ins to expose. Call it directly when you want the filtered ITool list itself, outside a toolkit: for inspection, for a custom aggregation, or to report which built-ins a given config would turn on before you actually build anything.

Why this and not the alternative

Create() for everything, Select(cfg) for the config-shaped subset

BuiltinTools.Create always returns all ten, unconditionally — no config, no filtering. Reach for Select the moment you need to honor a user- or agent-supplied builtins config value, including turning the whole source off.

Examples

1. null means all ten are on

using Toolnexus;

var tools = BuiltinTools.Select(null);

var names = tools.Select(t => t.Name).ToList();
var expected = new[] { "bash", "read", "write", "edit", "grep", "glob", "webfetch", "question", "apply_patch", "todowrite" };
if (!names.SequenceEqual(expected)) throw new Exception(string.Join(",", names));

Console.WriteLine($"ok: {tools.Count} built-ins, order: {string.Join(", ", names)}");

2. false turns the whole source off

using Toolnexus;

var off = BuiltinTools.Select(false);
if (off.Count != 0) throw new Exception($"expected 0 tools, got {off.Count}");

// A dict with disabled:true wins even if enabled:true is also present.
var alsoOff = BuiltinTools.Select(new Dictionary<string, object?> { ["enabled"] = true, ["disabled"] = true });
if (alsoOff.Count != 0) throw new Exception($"expected 0 tools, got {alsoOff.Count}");

Console.WriteLine("ok: false and disabled:true both turn every built-in off");

3. A tools map drops individual built-ins from the all-on baseline

using Toolnexus;

var cfg = new Dictionary<string, object?>
{
    ["tools"] = new Dictionary<string, object?>
    {
        ["bash"] = false,       // dropped
        ["apply_patch"] = false, // dropped
        ["read"] = true,        // stays on (redundant with the baseline)
        // everything else is unmapped -> stays on (all-on baseline)
    },
};

var tools = BuiltinTools.Select(cfg);
var names = tools.Select(t => t.Name).ToList();

if (names.Contains("bash") || names.Contains("apply_patch")) throw new Exception(string.Join(",", names));
if (!names.Contains("read") || !names.Contains("grep")) throw new Exception(string.Join(",", names));
if (names.Count != 8) throw new Exception($"expected 8, got {names.Count}: {string.Join(",", names)}");

Console.WriteLine($"ok: {names.Count} of 10 built-ins survive: {string.Join(", ", names)}");

cfg shapes

cfg	Result
null	All ten built-ins.
false	Empty list.
true	All ten built-ins.
{ "disabled": true, ... }	Empty list — wins over everything else.
{ "enabled": false, ... }	Empty list, unless disabled is also set (same outcome).
{ "tools": { name: bool } }	All-on baseline, minus any name mapped to false. Unknown names ignored.

See also

• BuiltinTools.Create — Construct every built-in tool directly, outside a toolkit.