Progressive Discovery

Progressive Discovery

Purpose

Implement the info/discovery tool pattern that helps users explore MCP server capabilities progressively. Prevent overwhelming users with too many tools by providing layered access to information: overview → category → specific tool → detailed documentation.

When to Use

Apply this pattern when:

• MCP server has 5+ tools
• Tool count will grow over time
• Tools group into logical categories
• Users need guidance on what's available
• Tool discovery is a problem

The Info Tool Pattern

Core Concept

Single entry point (info) that enumerates:

1. What exists - Tool categories and counts
2. How to learn more - Next discovery steps
3. Common workflows - Typical usage patterns

Example sparse table output:

Available Tools
===============

Query Tools (2)
  search      - Find code patterns
  find_files  - Search file names

Lookup Tools (2)
  get_definition  - Get symbol details
  find_references - Find usages

Use: get_help(tool_name) for detailed documentation

Implementation Patterns

Pattern 1: Single Info Tool

When: 5-15 tools, simple organization

// Pseudocode
function info() {
  return {
    categories: [
      {
        name: "Query Tools",
        count: 2,
        tools: [
          {name: "search", description: "Find code patterns"},
          {name: "find_files", description: "Search file names"}
        ]
      }
    ],
    next_steps: "Use get_help(tool_name) for details"
  }
}

Pattern 2: Layered Discovery

When: 15+ tools, complex organization

Layer 1 - Categories:

info()
  → Categories: query, lookup, analysis, management

Layer 2 - Category details:

info(category="query")
  → Tools in query category with descriptions

Layer 3 - Tool details:

get_help(tool="search")
  → Full documentation for search tool

Pattern 3: Mode-Based Discovery

When: Different user needs (quick ref vs comprehensive)

// Pseudocode
function info(mode = "overview") {
  if (mode === "overview") {
    // Sparse: just counts and categories
    return summaryCounts()
  } else if (mode === "tools") {
    // Medium: all tool names and one-line descriptions
    return toolList()
  } else if (mode === "comprehensive") {
    // Full: everything including examples
    return fullDocumentation()
  }
}

Output Format Examples

Sparse Table (Recommended for Overview)

Tool Groups
===========

Group        | Count | Avg Tokens | Performance
------------ | ----- | ---------- | -----------
query        | 3     | ~100       | Fast
lookup       | 4     | ~200       | Medium
analysis     | 2     | ~500       | Slow

Common Workflows:
  1. search → get_definition
  2. search → find_references → get_context

Use info(category="query") for details

Token cost: ~50 tokens

Benefits:

• Quick scan of capabilities
• Performance expectations set
• Clear next steps

JSON Array (Machine Parseable)

{
  "tool_groups": [
    {
      "name": "query",
      "count": 3,
      "avg_tokens": 100,
      "performance": "fast",
      "tools": [
        {"name": "search", "description": "Find code patterns"},
        {"name": "find_files", "description": "Search file names"},
        {"name": "list_symbols", "description": "List all symbols"}
      ]
    }
  ],
  "workflows": [
    {"name": "Find Implementation", "steps": ["search", "get_definition"]},
    {"name": "Understand Usage", "steps": ["search", "find_references", "get_context"]}
  ],
  "next_steps": {
    "category_detail": "info(category='query')",
    "tool_help": "get_help('search')"
  }
}

Token cost: ~150 tokens

Benefits:

• Machine readable for AI agents
• Structured for automation
• Complete capability map

Category Detail View

Query Tools
===========

search
  Purpose: Find code patterns across codebase
  Input: {pattern: string, filter?: string}
  Output: Array of {id, name, preview, confidence}
  Generates: result_id (use with get_definition)
  Performance: Fast (~100 tokens)

find_files
  Purpose: Search file names and paths
  Input: {pattern: string}
  Output: Array of {path, matches}
  Performance: Fast (~50 tokens)

list_symbols
  Purpose: List all symbols in a file
  Input: {file_path: string}
  Output: Array of {name, type, line}
  Performance: Medium (~200 tokens)

Token cost: ~200 tokens

Benefits:

• Focused on one category
• Shows input/output schemas
• Performance expectations
• Cross-tool relationships (IDs)

Progressive Detail Levels

Level 1: Counts Only (Most Sparse)

Tools: 12 total
  Query: 3
  Lookup: 4
  Analysis: 2
  Management: 3

Token cost: ~20 tokens When: Initial exploration, "what's available?"

Level 2: Names + One-Line (Sparse)

Query Tools (3):
  search       - Find code patterns
  find_files   - Search file names
  list_symbols - List symbols in file

Token cost: ~40 tokens When: "Show me query tools"

Level 3: Detailed Descriptions (Medium)

search
  Find code patterns across entire codebase
  Input: {pattern: string (regex), filter?: string}
  Output: {results: [{id, name, preview, confidence}], has_more, total}
  Generates: result_id for use with get_definition
  Example: search("function.*User")

Token cost: ~100 tokens When: "Tell me about search tool"

Level 4: Full Documentation (Verbose)

search - Code Pattern Search
============================

Purpose:
  Find code patterns using regex across entire codebase.
  Optimized for speed with result ranking by relevance.

Input Schema:
  {
    pattern: string (required) - Regex pattern to search
    filter: string (optional) - File filter (*.ts, src/**)
    max: integer (optional) - Max results (default: 50)
  }

Output Schema:
  {
    results: [{
      id: string - Use with get_definition
      name: string - Symbol name
      preview: string - Code snippet
      confidence: number - 0.0-1.0 match quality
    }],
    has_more: boolean - More results available
    total: integer - Total matches found
  }

Performance:
  Average: ~100 tokens
  Speed: <5ms typical

Cross-Tool Usage:
  1. search() → result_ids
  2. get_definition(id) → full details

Examples:
  Basic: search("User")
  Regex: search("function.*authenticate")
  Filtered: search("class", filter="src/**/*.ts")

Related Tools:
  - get_definition: Get full details for result
  - find_references: Find usages of symbol

Token cost: ~400 tokens When: "Give me everything about search"

Info Tool Implementation Guide

Pseudocode Structure

function info(options?: {
  mode?: "overview" | "category" | "tool",
  category?: string,
  tool?: string
}) {
  // Level 1: Overview (default)
  if (!options || options.mode === "overview") {
    return {
      format: "sparse_table",
      categories: getCategorySummary(),
      workflows: getCommonWorkflows(),
      next_steps: "info(category='name') for details"
    }
  }

  // Level 2: Category detail
  if (options.category) {
    return {
      format: "tool_list",
      category: options.category,
      tools: getToolsInCategory(options.category),
      next_steps: "get_help(tool_name) for full docs"
    }
  }

  // Level 3: Tool detail (redirect to get_help)
  if (options.tool) {
    return `Use get_help("${options.tool}") for detailed documentation`
  }
}

function get_help(tool_name: string) {
  // Full documentation for specific tool
  return getToolDocumentation(tool_name)
}

Output Format Decision Tree

User asks: "What can this MCP do?"
  → info() - Sparse table, ~50 tokens

User asks: "What query tools exist?"
  → info(category="query") - Tool list, ~100 tokens

User asks: "How do I use search?"
  → get_help("search") - Full docs, ~400 tokens

User asks: "Tell me everything"
  → info(mode="comprehensive") - Everything, ~1000+ tokens
  → WARN: Consider if this is actually helpful

Accept Extra Parameters Pattern

Critical learned lesson: Always accept extra/hallucinated parameters with warnings.

// Pseudocode
function info(options: any) {
  // Extract known parameters
  const {mode, category, tool, ...extra} = options || {}

  // Build response
  const response = buildInfoResponse(mode, category, tool)

  // Warn about unknown parameters (don't reject)
  if (Object.keys(extra).length > 0) {
    response.warnings = [
      `Unknown parameters ignored: ${Object.keys(extra).join(', ')}`
    ]
  }

  return response
}

Why: AI agents sometimes hallucinate parameters. Be permissive unless parameters cause severe issues.

Common Workflows Section

Always include common workflows in overview:

Common Workflows
================

Find Implementation:
  1. search("pattern") → result_ids
  2. get_definition(id) → full code

Understand Usage:
  1. search("class") → result_id
  2. find_references(id) → usage locations
  3. get_context(reference_id) → full context

Analyze Dependencies:
  1. search("module") → result_id
  2. analyze_dependencies(id) → dependency graph

Anti-Patterns to Avoid

❌ Dump Everything

function info() {
  // Returns 3000+ tokens
  return getAllToolsWithFullDocumentation()
}

Why bad: Overwhelming, wastes tokens

❌ No Categories

function info() {
  return [
    "search", "get_definition", "find_references",
    "get_context", "trace_callers", ... // 20 more
  ]
}

Why bad: No organization, hard to scan

❌ Reject Unknown Parameters

function info(options) {
  if (options.unknownParam) {
    throw new Error("Unknown parameter")
  }
}

Why bad: Brittle, rejects AI hallucinations unnecessarily

Real-World Examples

Lightning Code Index (lci)

info tool output (actual):
=========================

Search & Code Intelligence Tools
---------------------------------
  search          - Sub-ms semantic code search
  get_context     - Get detailed symbol context
  code_insight    - Multi-mode codebase analysis

Use search with --help flag for detailed options

Token cost: ~40 tokens Approach: Minimal, points to --help for details

Custom Info Tool Design

// Pseudocode for comprehensive info tool
function info(category?: string, detail_level: "sparse" | "medium" | "full" = "sparse") {
  const tools = getToolMetadata()

  if (detail_level === "sparse") {
    // Counts only
    return {
      total: tools.length,
      by_category: groupCounts(tools)
    }
  }

  if (category) {
    // Category-specific
    const filtered = tools.filter(t => t.category === category)
    return {
      category,
      count: filtered.length,
      tools: filtered.map(t => ({
        name: t.name,
        description: t.description,
        generates: t.generates,
        consumes: t.consumes
      }))
    }
  }

  // Full overview
  return {
    categories: getCategoriesWithTools(tools),
    workflows: getWorkflows(),
    performance: getPerformanceGuide()
  }
}

Additional Resources

Reference Files

• references/info-tool-templates.md - Complete info tool templates for different MCP sizes
• references/layered-help.md - Advanced multi-layer help systems

Examples

• examples/info-tool-small.ts - Info tool for 5-10 tool MCP
• examples/info-tool-large.ts - Info tool for 20+ tool MCP
• examples/info-tool-modes.ts - Mode-based discovery implementation

Quick Reference

Info tool checklist:

• Returns sparse overview by default
• Groups tools by category/domain
• Shows tool counts per category
• Includes common workflows
• Provides next steps for detail
• Accepts extra parameters with warnings
• Uses sparse tables for human readability
• Provides JSON format for automation
• Token cost < 100 for overview
• Progressive detail levels implemented

Progressive layers:

1. Overview - Categories, counts, workflows (~50 tokens)
2. Category - Tools in category with descriptions (~100 tokens)
3. Tool - Single tool full documentation (~400 tokens)
4. Comprehensive - Everything (use sparingly, ~1000+ tokens)

Focus on helping users discover capabilities without overwhelming them with information.