Go Toolbroker

go-toolbroker

[](https://pkg.go.dev/github.com/hollis-labs/go-toolbroker)

go-toolbroker is an in-process Go library for intent-aware MCP tool selection. Given a registry of MCP tool definitions and a priority-ordered set of rules, it selects the subset of tools relevant to a user's detected intent — replacing hardcoded exclude lists with a flexible rule engine. It also ships keyword-based intent detection, token-budget estimation, progressive-discovery scoring helpers, and an optional per-tool enrichment pipeline (Hints → markdown override block).

Consumers (chat clients, agent runtimes, anything that talks to many MCP servers in one process) use it to keep per-turn tool payloads small and on-topic.

Status

Pre-1.0. The public API is stable enough to be embedded in production code; expect minor additive changes between v0.x releases. A future remote/HTTP broker implementation is on the roadmap; only LocalBroker ships today.

Install

go get github.com/hollis-labs/go-toolbroker

import "github.com/hollis-labs/go-toolbroker/broker"

Quickstart

package main

import (
    "context"
    "fmt"

    "github.com/hollis-labs/go-toolbroker/broker"
)

func main() {
    // 1. Define a tiny rule set (or load from a file with broker.LoadRulesFromFile).
    rules := []broker.Rule{
        {
            Name:     "hide-noisy-build-tools",
            Intent:   "*",
            Priority: 10,
            Match:    broker.Match{Patterns: []string{"build_*"}},
            Action:   broker.Action{Type: "exclude"},
        },
        {
            Name:     "show-build-tools-on-build-intent",
            Intent:   "run_build",
            Priority: 20,
            Match:    broker.Match{Patterns: []string{"build_*"}},
            Action:   broker.Action{Type: "include"},
        },
    }

    // 2. Create a broker and register your discovered MCP tools.
    b := broker.NewLocalBroker(nil, rules)
    b.RegisterTools([]broker.ToolDefinition{
        {Name: "tasks_list", Description: "List tasks", Server: "tasks"},
        {Name: "tasks_create", Description: "Create a task", Server: "tasks"},
        {Name: "build_go_project", Description: "Build a Go project", Server: "ci"},
    })

    // 3. Detect intent from the user's message and ask for relevant tools.
    intents := broker.DetectIntent("create a new task for the backend")
    intent := "*"
    if len(intents) > 0 {
        intent = intents[0].Name
    }
    result, err := b.SelectTools(context.Background(), intent, nil)
    if err != nil {
        panic(err)
    }
    fmt.Printf("selected %d/%d tools: %s\n", result.Count, result.Total, result.Rationale)

    // 4. (Optional) Prune further to fit a token budget.
    pruned := broker.PruneToTokenBudget(result.Tools, 40000)
    _ = pruned
}

For runnable end-to-end programs, see the [examples/](examples/) directory:

• examples/basic — minimal selection with hand-written rules.
• examples/yaml-rules — load rules from a YAML file at runtime.
• examples/enrichment — wire an Enricher so SelectResult.OverrideBlock is populated with per-tool hints.

API Overview

All exports live in the single broker package.

Core broker (broker.go, local.go)

• Broker interface — SelectTools(ctx, intent, hints) and AllTools().
• LocalBroker — rule-based, in-process implementation of Broker.
• NewLocalBroker(tools, rules, opts...) *LocalBroker
• (*LocalBroker).RegisterTools, LoadRules, AllTools, SelectTools
• Data types: ToolDefinition, ToolSummary, SelectResult.

Rules and configuration (rule.go, config.go)

• Rule, Match, Action — describe priority-ordered selection rules.
• Config — top-level YAML/JSON shape ({rules: [...]}).
• LoadConfig(path) — parse a JSON config file.
• LoadRulesFromFile(path) — parse YAML or JSON rules; format auto-detected by extension.
• DefaultRules() — returns example rules embedded from broker/default-rules.yaml. The bundled defaults reference a specific MCP toolset and are intended as a worked example of the rule format, not as production defaults — most consumers will write their own rules.

Intent detection (intent.go)

• Intent{Name, Confidence, Keywords}
• DetectIntent(message) []Intent — keyword-based (no ML), ranked by confidence.

Progressive discovery / scoring (discovery.go)

• ScoreByKeywords(tools, keywords, maxResults)
• ScoreByIntent(tools, intent, maxResults)
• FindByNames(tools, names)
• TokenizeIntent(intent)
• MinKeywordScore constant.

Token budget (budget.go)

• EstimateToolTokens(tools) int
• PruneToTokenBudget(tools, budgetTokens) []ToolDefinition
• DefaultTokenBudgetPct, DefaultContextWindowTokens constants.

Enrichment (hints.go, enricher.go, override.go)

• Hints{Preconditions, AntiPatterns, ChainsWith, OutputShape} — per-tool metadata that shapes the agent's use of a tool without changing the tool's schema.
• MarshalHints / UnmarshalHints — JSON codec for storage in a consumer-owned table.
• Enricher interface — LookupByToolName(ctx, name) (Hints, bool, error). Consumers back this with their own storage (SQLite, in-memory, remote service, ...). A NopEnricher is provided as a safe default.
• ComposeOverrideBlock(ctx, toolNames, enr) (string, error) — produces a compact markdown ## Tool Overrides section summarizing hints for the named tools. Tools without hints are skipped.
• WithEnricher(Enricher) Option — functional option on NewLocalBroker. When set, SelectTools populates SelectResult.OverrideBlock (markdown ready to append to the per-turn system prompt) from the selected tools' hints.

Storage for enrichment records is consumer-owned — this package ships only the interface, composition, and the no-op default. A consumer that already persists per-tool metadata can satisfy Enricher with a single method.

Logging

go-toolbroker uses the standard library log/slog package on the default handler. Only the enrichment compose-error path logs today (a slog.WarnContext at "toolbroker: compose override block failed"); selection never logs on the happy path. Enrichment failures are logged and then swallowed so selection remains successful — logging is observation, not control flow.

Callers who want structured logging should configure their own handler via slog.SetDefault(slog.New(...)) at process start; the broker will honor it automatically.

Selection algorithm

LocalBroker.SelectTools (see broker/local.go):

1. Sort rules by Priority descending.
2. Filter to rules whose Intent glob (via path.Match, with ""/"*" = all) matches the incoming intent.
3. Start with the full tool set. For each applicable rule, apply exclude (blacklist), include (whitelist, cumulative), or summarize (currently behaves like include — reserved for future progressive disclosure).
4. If any include rule fired, only explicitly included tools are kept. Exclusions always win over includes.
5. Tool-name patterns support both path.Match glob semantics and a HasPrefix fallback for patterns ending in * (so build_* matches build_go_project).

LocalBroker uses an internal sync.RWMutex, so registration, rule loading, and tool selection can be called concurrently from multiple goroutines.

For deeper integration patterns — including intent detection feeding tool routing, token budgeting, and a request_tools progressive-discovery meta-tool — see [docs/integration-guide.md](docs/integration-guide.md).

Dependencies

Only one external dependency:

• gopkg.in/yaml.v3 — YAML parsing for rule files and the embedded default-rules.

Everything else is the Go standard library (context, encoding/json, embed, os, path, sort, strings, log/slog, sync).

Testing

go test ./...
go test -race ./...

No external services, fixtures, or environment variables are required. Tests use t.TempDir() for any file I/O and cover broker selection, rule loading (JSON/YAML/YML), default rules, intent detection, scoring, token budgeting, and enrichment composition.

License

MIT — see [LICENSE](LICENSE).

Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: hollis-labs
• Source: hollis-labs/go-toolbroker
• License: MIT
• Homepage: https://pkg.go.dev/github.com/hollis-labs/go-toolbroker

Install and usage instructions live in the source repository linked above.