longpath

An MCP server that lets an assistant (Claude Code, GitHub Copilot agent mode, any MCP client) read and analyze construction / project schedules the way a scheduler would: its own CPM engine, float, critical and driving paths, the DCMA 14-point assessment, logic-quality checks, update-to-update comparison, baseline variance and S-curve data.

Schedule files are only ever read. .xer and MS Project XML need nothing but Python; without the optional extra and Java, a .mpp fails with a message saying exactly what to install.

Tools

Every tool takes the schedule's absolute path. Every list returns count plus the top limit rows (default 25) and says when it truncated. Durations and float are working days on each activity's own calendar unless a field ends in _h.

Install

pip install longpath          # or run it without installing: uvx longpath

Needs Python 3.11+. That is all .xer and MS Project XML files need.

MS Project .mpp and P6 XML (optional). These go through MPXJ, a Java library:

1. Install the extra, which pulls in the mpxj package for its bundled jars: pip install "longpath[mpp]" (with uvx: uvx --from "longpath[mpp]" longpath).
2. Install any Java 11+ runtime (JDK or JRE, e.g. Eclipse Temurin). longpath looks for it in java_home in longpath.toml, then JAVA_HOME, then java on PATH.

Run check_setup to see what was found. The MPXJ jars can also come from a folder of your own (mpxj_classpath). Without Java, MS Project's File > Save As > XML produces a file longpath reads natively.

Claude Code

claude mcp add --scope user longpath -- uvx longpath
# with .mpp support:
claude mcp add --scope user longpath -e JAVA_HOME=/path/to/jdk -- uvx --from "longpath[mpp]" longpath

VS Code / Copilot. Add to the user-level mcp.json (MCP: Open User Configuration), so it works in every window:

"longpath": {
  "type": "stdio",
  "command": "uvx",
  "args": ["--from", "longpath[mpp]", "longpath"],
  "env": { "JAVA_HOME": "C:\\path\\to\\jdk-21" }
}

(Drop --from longpath[mpp] and the env block if you only read .xer / XML: "args": ["longpath"].)

Configuration (optional)

Every setting is optional. Copy longpath.example.toml to one of these (first match wins):

1. the file named by LONGPATH_CONFIG
2. longpath.toml in the server's working folder
3. longpath.toml in LONGPATH_HOME, default %LOCALAPPDATA%\longpath\ on Windows, ~/.local/share/longpath/ elsewhere

Unknown keys are rejected with the list of allowed ones. No secrets are involved and nothing is sent anywhere: the server makes no network calls.

Safety model

• Read-only by design. Every tool opens the schedule for reading only; MPXJ conversions write to a private temp folder that is deleted afterwards. All tools except export_csv carry readOnlyHint.
• export_csv is the only write. It creates a new .csv file (UTF-8 with BOM for Excel) and refuses existing files, non-.csv paths and relative paths. It is a dry run by default (row count, columns, first rows) and writes only with dry_run=false and allow_writes = true in the config. Undo = delete the file.

The CPM engine

P6 rules, computed from the logic in the file (not copied from its stored dates):

• FS / SS / FF / SF with positive and negative lags; lag calendar per the P6 option (predecessor, successor, 24-hour, project default).
• Each activity on its own calendar at minute resolution: work weeks with split shifts, holidays, changed-hours days, 24-hour and 6/7-day calendars. Starts land on the first working minute (Mon 08:00), finishes at the end of the last working interval (Fri 17:00).
• Constraints: Start/Finish On or After/Before, Start On / Finish On, Mandatory Start/Finish (breaks logic, as in P6), As Late As Possible, P6 external early/late dates, MS Project deadlines (as finish-on-or-before), project must-finish date.
• Progress: data date floor, actual dates, in-progress remaining work under Retained Logic or Progress Override (from the file's schedule options). Completed activities are fixed and have no float.
• Total float per the file's setting (finish, start, or smaller of the two), free float, relationship float, driving flags, longest path, critical by the project's float threshold. Level-of-effort and WBS-summary activities are left out of the network. Logic loops are detected and listed instead of producing garbage.

Validation

• Known-answer tests on hand-built XERs: every relationship type, leads, lags, holidays, mixed calendars, SNET / FNLT / Mandatory Start, must-finish, retained logic vs progress override, open ends, LOE, loops.
• MPXJ's public sample files (131 MS Project schedules), read two ways (.mpp → MS Project XML, and the XER MPXJ writes): all load and every tool runs on every file. Computed total float matched the slack MS Project stored for about 96% of activities (3,910 of 4,065 via XER; 3,880 of 4,047 via .mpp). Every remaining difference traced so far is an MS Project vs P6 rule difference (see limits); the same file read both ways gives identical floats.
• 20,000 activities / 40,000 relationships (scripts/make_big_xer.py): open + CPM about 0.8 s, DCMA about 1 s.
• scripts/sweep_samples.py <folder> re-runs the stored-float comparison over any folder of schedules.

Known limits

• Not yet validated against a broad set of P6-calculated XERs. The P6 rules are verified by hand-worked answers, and the large sample sweep came from MS Project files. If run_cpm disagrees with the float P6 stored in your file, an issue with the comparison_with_file output is very welcome.
• Resource-dependent activities use the activity calendar (resource calendars and leveling are not modelled).
• ALAP is approximated (the activity is pushed late by its free float). P6 "expected finish", suspend/resume and multi-project scheduling across files are not modelled; relationships to other projects count as external.
• MS Project differs from P6 on slack for SS/SF-linked predecessors, summary-task logic (dropped here, with a warning), manually scheduled tasks and resource-calendar-driven tasks, so stored MS Project slack will not always match.
• S-curves spread quantities linearly over working time (no resource curves or timephased data). MS Project "cost" is cost at completion; its Baseline (0) is the planned curve when present.
• DCMA thresholds are the standard ones and fixed; "high duration" uses original duration; missed tasks, BEI and CPLI need a baseline (a baseline file, MS Project Baseline 0, or P6 planned dates, labelled as such).
• Percentage lags (MS Project) are converted to hours of the predecessor's duration; elapsed lags are treated as working time.
• Password-protected .mpp files cannot be read.

Layout

src/longpath/ — xer.py / mspdi.py / mpxj_bridge.py → model.py (one normalized model) → calendars.py (work-time timeline) → cpm.py → checks.py (DCMA + logic) / compare.py (updates, baseline) / curves.py (S-curve) → analysis.py (shared row shaping) → server.py (the tools). tests/xerbuild.py builds known-answer XERs.

Development

git clone https://github.com/S-CurveLabs/longpath; cd longpath
python -m venv .venv
.venv\Scripts\pip install -e .[mpp,dev]
.venv\Scripts\pytest

The tests that go through MPXJ run only when Java is found (JAVA_HOME or PATH) and skip otherwise. The fixtures in tests/fixtures/ are synthetic; scripts/make_fixtures.py rebuilds them (see tests/fixtures/README.md).

License

MIT. The optional mpxj package is a separate LGPL library that longpath runs as a converter; it is not bundled.