Replace the body content of a specified Swift symbol while preserving the declaration.
AI agents use swift_replace_symbol_body to create or update resources in SwiftLens — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your SwiftLens environment.
This tool modifies Swift source code by replacing symbol bodies. While changes are technically reversible (can be undone via version control or subsequent edits), the tool enables an AI agent to alter executable code logic across a codebase without deletion. This is a Write operation rather than Execute because the tool itself doesn't run the code—it modifies it.
From the tool's definition Tool description states: 'Replace the body content of a specified Swift symbol while preserving the declaration.' This directly modifies source code by replacing function/method/property bodies, creating reversible changes to the codebase.
Documented attack patterns abuse exactly the kind of access swift_replace_symbol_body gives an agent:
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_replace_symbol_body:
{
"version": "1",
"default": "deny",
"tools": {
"swift_replace_symbol_body": {
"limits": [
{
"counter": "swift_replace_symbol_body_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}swift_replace_symbol_body stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Replace the body content of a specified Swift symbol while preserving the declaration. It is categorised as a Write tool in the SwiftLens MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the SwiftLens MCP server in PolicyLayer and add a rule for swift_replace_symbol_body: 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.
swift_replace_symbol_body is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the swift_replace_symbol_body 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.
Set action: deny in the PolicyLayer policy for swift_replace_symbol_body. 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.
swift_replace_symbol_body 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.
Deterministic rules across all 15 SwiftLens tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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15 SwiftLens tools catalogued and risk-classified — across an index of 42,500+ MCP servers.