// MCP TOOL REFERENCE

swift_build_index

ServerSwiftLens
CategoryExecute

WHAT SWIFT_BUILD_INDEX ON SWIFTLENS DOES

AI agents invoke swift_build_index to trigger actions in SwiftLens. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

THE RISK

High Risk

This tool executes an external build process (Swift compiler) with configurable arguments. While the specific command appears benign (building an index for LSP), it is fundamentally an Execute operation because it triggers compilation and external tool invocation.

From the tool's definition Tool runs `swift build` command with specific compiler flags (-index-store-path). The description explicitly states it 'Runs' a build command, which is code execution.

Documented attack patterns abuse exactly the kind of access swift_build_index gives an agent:

HOW TO CONTROL SWIFT_BUILD_INDEX

PolicyLayer is an MCP gateway — it sits between your AI agents and SwiftLens, and nothing reaches the server without passing your rules. This is the rule we recommend for swift_build_index:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "swift_build_index": {
      "limits": [
        {
          "counter": "swift_build_index_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

swift_build_index stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register SwiftLens — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

More SwiftLens tools

Write swift_replace_symbol_body Replace the body content of a specified Swift symbol while preserving the declaration. Read get_tool_help Get concise help for Swift tools. Pass tool_name for specific help, or None for all tools. Read swift_analyze_files Analyze Swift files and extract symbol structures (supports single or multiple files). Read swift_check_environment Check if Swift development environment is properly configured. Read swift_find_symbol_references_files Find all references to a symbol across multiple Swift files. Prefer relative paths (e.g., Read swift_get_declaration_context Get fully-qualified declaration contexts for all symbols in a Swift file. Read swift_get_file_imports Extract import statements from a Swift file. Read swift_get_hover_info Get hover information for a symbol at the specified position in a Swift file.

All 15 SwiftLens tools →

Execute tools on other servers

Frida Game Hacking MCP remove_breakpoint Procmon request_elevation WireMCP capture_packets Pentest Ai run_probe

Go deeper

High-risk tools in SwiftLens → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

What does the swift_build_index tool do? +

Build or rebuild Swift project index for better LSP functionality. Runs swift build -Xswiftc -index-store-path -Xswiftc .build/index/store to generate the index that enables cross-file symbol resolution and references. It is categorised as a Execute tool in the SwiftLens MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on swift_build_index? +

Register the SwiftLens MCP server in PolicyLayer and add a rule for swift_build_index: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches SwiftLens. Nothing to install.

What risk level is swift_build_index? +

swift_build_index is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit swift_build_index? +

Yes. Add a rate_limit block to the swift_build_index rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block swift_build_index completely? +

Set action: deny in the PolicyLayer policy for swift_build_index. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides swift_build_index? +

swift_build_index is provided by the SwiftLens MCP server (swiftlens/swiftlens). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every SwiftLens tool call.

Deterministic rules across all 15 SwiftLens tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.

GOVERN SWIFTLENS →

Free to start. No card required.

15 SwiftLens tools catalogued and risk-classified — across an index of 42,500+ MCP servers.

swift_build_index

// WHAT SWIFT_BUILD_INDEX ON SWIFTLENS DOES

// THE RISK

// HOW TO CONTROL SWIFT_BUILD_INDEX

// EXPLORE