Tool Selector Protocol

Determine which tools are needed to solve the task, plan the most efficient sequence, and eliminate unnecessary calls before they happen.

Core principle: Every tool call costs time, tokens, and rate limits. The right tool, in the right order, called once.

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Tool Catalog

Tool	Cost	Side Effect	Best For
Web search	Medium	None (read-only)	Current info, external sources
Code execution	Medium	Environment-dependent	Computation, transformation, testing
File read	Low	None	Local data, config, content
File write	Medium	Persistent change	Saving output, updates
API call	High	Rate limits, cost	External service integration
Database query	Medium-High	Persistent on writes	Data read/write
Memory/context	Low	None	Retrieve previous information

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Selection Algorithm

For each tool candidate, ask these questions in order:

1. Can this tool actually solve this task?           → No = eliminate
2. Can a cheaper/simpler tool do the same job?       → Yes = use that instead
3. Was this tool already called for this task?        → Yes = use cached result
4. Is this call actually needed right now?            → No = defer
5. Does this tool depend on another tool's output?    → Yes = add to sequence

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Anti-Patterns — Block These

Anti-Pattern	Problem	Solution
Reading the same file repeatedly	Each read costs tokens	Cache on first read
Web search for known information	Unnecessary latency	Use existing knowledge
Serial API calls (could be parallel)	Slow	Plan parallel calls
Tool chain when one tool suffices	Extra steps	Consolidate
Read before write (when unnecessary)	Extra call	Skip the read
Loading memory every step	Token waste	Load once, reference

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Output Format

TOOL SELECTOR
Task    : [task summary]
Selected: N tools | Total calls: N | Blocked: N

## Tool Plan

| Step | Tool | Purpose | Depends On | Cached? |
|------|------|---------|------------|---------|
| 1 | [tool] | [why] | — | No |
| 2 | [tool] | [why] | #1 | Yes — use #1 output |

## Blocked Calls

| Blocked | Reason | Alternative |
|---------|--------|-------------|
| [tool call] | [rationale] | [what to do instead] |

## Optimization Notes
- [Parallel opportunities]
- [Cached outputs]
- [Rate limit warnings]

Approve? Proceed?

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Tool Combination Guide

Task Type	Typical Chain	Block
Research & Report	Search → File read → Code (analyze) → File write	Searching same topic twice
Data Processing	File read → Code → File write	Re-reading file each step
API Integration	Memory (creds) → API → Code (parse) → DB write	Re-auth per request
Code Development	File read → Code (test) → File write → Code (verify)	Full test suite on every change
Database Operation	Memory (schema) → DB (SELECT) → Code (prepare) → DB (write)	Running same SELECT twice

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When to Skip

• Single-tool task ("read this file")
• User already specified which tool to use
• Single-step, side-effect-free task

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Guardrails

• Never call an API when cached data suffices — always check cache first.
• Prefer low-cost tools — file read over web search when local data exists.
• Cross-skill: works with parallel-planner (parallel tool calls) and task-decomposer (tool needs per subtask).