Your MCP anonymizer is self-defeating if it takes code as an argument
Aggressive-Course-24 · reddit · 2026-09-30
An MCP server maintainer explains a load-bearing design decision for source-code anonymization: tools that accept code as an argument are self-defeating, since the identifiers are already in the model's context by the time masking runs. Instead, tools should take a file path, mask it server-side, and return stable masked names that can be un-masked on the way back.
Supporting constraints:
- --root scopes readable paths to block path traversal attacks (e.g., being talked into reading /.ssh/idrsa);
- zero runtime dependencies, hand-rolled JSON-RPC framing;
- stdout is protocol-only, diagnostics to stderr;
- failures return as tool errors so the model can self-correct.
Honest gap exposure: result headers include lines that appear only when applicable — a warning when no language marker matched, and a count of real names/ticket numbers left in comments.
One-way redaction: detected credentials are replaced by tokens that never enter the restore map, since reversible masking of secrets would be a vulnerability shipped as a feature.
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