file-mcp

file-mcp is a Windows-first MCP server focused on deterministic text writes. It intentionally exposes write-only tools for create, replace, and structured edit workflows. Public read and search capabilities have been removed from the tool surface.

Goals

• Keep the MCP surface focused on writing files

• Preserve encoding, BOM, newline style, and trailing newline by default when editing existing files

• Support atomic writes guarded by base_hash

• Handle chunked large-file generation without giant single-call payloads

• Keep existing mixed-newline files writable without forcing full normalization first

Related MCP server: local-code-mcp

Tool Surface

• write_full_text(path, content, encoding="preserve", bom="preserve", newline="preserve", final_newline="preserve", create_dirs=True, if_exists="overwrite", base_hash=None) Whole-file atomic write.

• apply_text_edits(path, edits, encoding="preserve", bom="preserve", newline="preserve", final_newline="preserve", base_hash=None) Atomic line-range edits. Each edits[] item must provide start_line and new_text; end_line and expected_old_text are optional.

• apply_text_spans(path, spans, encoding="preserve", bom="preserve", newline="preserve", final_newline="preserve", base_hash=None) Atomic offset-based edits using normalized-text offsets. Each spans[] item must provide start_offset, end_offset, and new_text; expected_old_text is optional.

• replace_literal(path, old_text, new_text, encoding="preserve", expected_occurrences=1, bom="preserve", newline="preserve", final_newline="preserve", base_hash=None) Exact-count literal replacement. When no exact match is found, the server also tries conservative mojibake recovery for non-ASCII old_text/new_text pairs before failing and reporting whitespace or codec hints.

• replace_regex(path, pattern, replacement, encoding="preserve", expected_occurrences=1, case_sensitive=True, dotall=False, bom="preserve", newline="preserve", final_newline="preserve", base_hash=None) Exact-count regex replacement.

• replace_block(path, start_marker, end_marker, replacement, encoding="preserve", occurrence=1, mode="between", bom="preserve", newline="preserve", final_newline="preserve", base_hash=None) Marker-delimited block replacement.

• begin_write_session(path, encoding="preserve", bom="preserve", newline="preserve", final_newline="preserve", create_dirs=True, if_exists="overwrite", base_hash=None)

• append_write_chunk(session_id, content)

• commit_write_session(session_id)

• abort_write_session(session_id)

What Changed

• inspect_text was removed from the public MCP interface

• read_text was removed from the public MCP interface

• search_text was removed from the public MCP interface

• apply_search_replacements was removed from the public MCP interface

The server still reads existing file contents internally when a write operation needs style preservation, conflict checks, or targeted replacement. That internal read path is now an implementation detail rather than a client-facing capability.

Editing Model

Recommended usage now is:

1. Use a caller-side source of truth for the target file content or edit coordinates.

2. Choose one write primitive: write_full_text, apply_text_edits, apply_text_spans, replace_literal, replace_regex, or replace_block.

3. Pass base_hash when you already have a trusted hash and want fail-closed concurrency protection.

4. Use chunked sessions for large generated outputs.

Return Format

Successful write tools return compact natural-language summaries for LLM attention hygiene. The default result includes only the operation outcome, target path, and essential counts or session id.

Examples:

Created C:\work\repo\README.md.
Updated C:\work\repo\src\app.ts: replaced 1 occurrence.
Unchanged C:\work\repo\README.md: new content matched existing file.
Write session started for C:\work\repo\large.txt. Session: 8f6c2c4e0f134f49a6b48bbf55f7156a
Committed write session 8f6c2c4e0f134f49a6b48bbf55f7156a to C:\work\repo\large.txt: updated file.

The tool output intentionally omits audit fields such as hashes, byte counts, encoding, newline style, and total line counts.

Nested Edit Objects

apply_text_edits item fields:

• start_line: 1-based inclusive line number.

• end_line: optional 1-based inclusive end line. Omit to replace only start_line; set to start_line - 1 to insert before start_line.

• new_text: replacement text for the line range.

• expected_old_text: optional guard text for the existing line range.

apply_text_spans item fields:

• start_offset: 0-based inclusive offset in normalized file text.

• end_offset: 0-based exclusive offset in normalized file text.

• new_text: replacement text for the offset range.

• expected_old_text: optional guard text for the existing normalized offset range.

Style Preservation

When editing an existing file with the default "preserve" modes:

• encoding keeps the detected file encoding

• bom keeps the existing BOM state

• newline keeps LF, CRLF, or CR

• final_newline keeps whether the file ended with a newline

If the existing file uses mixed newline styles and you keep newline="preserve", unchanged or positionally corresponding lines retain their original endings and inserted lines use the dominant existing newline style.

Allowed Roots

By default the server only allows access under F:\.

Override with an environment variable:

$env:FILE_MCP_ALLOWED_ROOTS = 'F:\;F:\GGPK3\;F:\repo\'

Multiple roots are separated with ;. Set FILE_MCP_ALLOWED_ROOTS to * to disable root restrictions entirely.

Install

cd D:\file-mcp
py -m pip install -e .

Run

cd D:\file-mcp
py -m file_mcp

Example MCP Client Config

{
  "mcpServers": {
    "file-mcp": {
      "command": "py",
      "args": ["-m", "file_mcp.server"],
      "cwd": "D:\\file-mcp",
      "env": {
        "FILE_MCP_ALLOWED_ROOTS": "*"
      }
    }
  }
}

Notes

• Auto-detection supports UTF-8, UTF-8 BOM, UTF-16 LE/BE, UTF-32 LE/BE, and gb18030, and it now prefers gb18030 over UTF-8 only when both decoders succeed and the UTF-8 result looks materially more like mojibake

• Successful write tools return compact natural-language summaries instead of JSON metadata

• write_full_text is the simplest primitive when whole-file replacement is acceptable