Engineer MCP

Engineer MCP is a Model Context Protocol server for mechanical-engineering calculations. It gives coding agents verified answers for beams, bolts, springs, shafts, bearings, stress, sections, fits, and units. Every result shows the formula, the method, and the source.

Release 0.11 adds shaft combined load-case comparison with von Mises safety factors and source-linked report rows. Release 0.10 adds signed dimensional tolerance stacks with worst-case and independent RSS bounds. Use stdio for desktop clients. Use HTTP for local services and network clients.

What it provides

Use Engineer MCP inside an AI coding agent. The agent calls a tool and receives a complete engineering answer. The answer includes numbers, units, assumptions, and citations.

The release covers these domains:

• Beam bending stress and deflection.

• Bolt tensile design to ISO 898.

• Helical compression spring design.

• Shaft torsion and first critical speed.

• Shaft combined bending and torque load-case comparison on round sections.

• Bearing rating life to ISO 281.

• von Mises equivalent stress.

• Fatigue analysis for cyclic loads.

• Cross-section properties.

• Press and shrink fit analysis by Lamé theory.

• Standard steel section catalog to EN 10365. The catalog returns the separate source for published section properties.

• Bearer authentication and browser origin allow-lists for HTTP clients.

• Dimension-safe unit conversion, including viscosity and thermal conductivity.

• Signed dimensional tolerance stacks with worst-case and independent RSS bounds.

• Material property lookup.

• Stdio and HTTP transports. The HTTP mode serves the same tools over the Streamable HTTP protocol.

Related MCP server: eq-reference-mcp

How results stay trustworthy

Each result carries its provenance. The envelope lists the method, the formula, and the notes. It also lists the cited standards and texts.

Units are checked at every step. The unit layer knows the dimension of every unit. It rejects a conversion between incompatible quantities. For example, it rejects a torque-to-energy conversion.

Safety factors appear only when you provide the data they need. The tool never hides an assumption. Warnings surface when a method uses an approximation.

Tools

See docs/mcp-tools.md for the full reference. See docs/section-catalog.md for the covered range, the value provenance, and the data audit. See docs/units.md for the unit model and the full category list. See docs/transport.md for the HTTP transport reference. See docs/tolerance-stack.md for the stack model and assumptions. See docs/shaft-load-cases.md for the load-case model and limits. See ROADMAP.md for release status and future milestones.

Architecture

Engineer MCP keeps the math separate from the server. Pure engine functions take SI numbers and return plain objects. The server layer adds unit conversion, material lookup, and provenance. The database seeds from JSON files on first start.

flowchart LR
  Agent[AI coding agent] -->|stdio| Server[MCP server]
  Agent -->|HTTP| Security[HTTP security policy]
  Security --> Server
  Server --> Tools[Tools layer]
  Tools --> Engines[Calculation engines]
  Tools --> Units[Unit layer]
  Tools --> Db[SQLite data]
  Engines --> Provenance[Method and references]

Key directories:

Quick start

1. Install Node.js 22.13 or newer.

2. Clone or copy this repository to your machine.

3. Run npm ci to install the locked dependencies.

4. Run npm run build to compile the server.

5. Run npm run demo to see the demo output.

The demo prints results for every tool. It runs against an in-memory database. It needs no API keys and no network access.

Configure HTTP authentication with ENGINEER_MCP_AUTH_TOKEN. Configure browser access with ENGINEER_MCP_ALLOWED_ORIGINS.

Run as an MCP server

Run the server over standard input and output.

node dist/index.js

Add it to your MCP client configuration. See examples/mcp-config.example.json for a template. Set ENGINEER_MCP_DB or pass --db <path> to choose the database file. The default database file is engineer-mcp.sqlite in the working directory.

Run over HTTP

Run the server with the HTTP transport.

node dist/index.js --transport http

The server listens on http://127.0.0.1:3000/mcp. Set --host and --port to change the bind address. Set --response-mode sse when the client requires Server-Sent Events. The default response mode is JSON. Set ENGINEER_MCP_TRANSPORT, ENGINEER_MCP_HOST, and ENGINEER_MCP_PORT to configure the same values. Set ENGINEER_MCP_HTTP_RESPONSE_MODE to json or sse. See docs/transport.md for client configuration and curl examples.

Use a port of 0 to let the operating system choose a free port. The server prints the real port to standard error.

Sample output

A local HTTP client can connect to the MCP endpoint:

HTTP transport listening at http://127.0.0.1:3000/mcp
POST /mcp initialize                         200 OK
POST /mcp tools/call unit_convert            200 OK
Converted value                              1000 cP

A call to beam_bending with a 20 kN point load on a 3 m S355 I-beam:

Maximum bending moment                  15 kN·m
Maximum bending stress               25.36 MPa
Maximum deflection                  0.6039 mm
Bending safety factor                    14

Method: Euler-Bernoulli beam theory
Formula: simply supported, point: M = FL/4, delta = FL^3/(48EI)
References:
  - Roark's Formulas for Stress and Strain (Eighth edition, 2011)
  - Mechanics of Materials (Euler-Bernoulli beam theory)

A call to spring_design for a steel spring under 2 kN with squared and ground ends:

Spring index                              5
Wahl factor                            1.31
Total coils                               6
Solid height                             48 mm
Spring rate                           158.6 N/mm
Deflection at load                    12.61 mm
Working length                        77.39 mm
Maximum shear stress                  521.4 MPa
Spring safety factor                  1.342

Method: Helical compression spring design
Formula: C = D/d, K_w = (4C-1)/(4C-4) + 0.615/C, tau = K_w 8FD/(pi d^3), k = G d^4/(8 D^3 Na), delta = F/k, Ls = d Nt
References:
  - Shigley's Mechanical Engineering Design (Tenth edition, 2015)
  - Machinery's Handbook (Thirty-first edition)

A call to interference_fit for a steel hub on a solid steel shaft with 50 µm of diametral interference:

Interface pressure                    77.62 MPa
Hub tangential stress                 129.4 MPa
Shaft tangential stress               77.62 MPa
Axial force capacity                  73.16 kN
Torque capacity                       1.829 kN·m
Shaft safety factor                   3.865
Hub safety factor                     1.656
Torque safety factor                  1.829

Method: Interference fit by Lamé thick-cylinder theory
Formula: p = delta / (d K); K = (1/Eh)((Ro^2+r^2)/(Ro^2-r^2)+nu_h) + (1/Ei)((r^2+ri^2)/(r^2-ri^2)-nu_i); F = 2 pi r L p mu; T = F r
References:
  - Shigley's Mechanical Engineering Design (Tenth edition, 2015)
  - Machinery's Handbook (Thirty-first edition)
  - Theory of Elasticity (Lamé solution for thick-walled cylinders)

A call to fatigue_analysis for a ground steel part at 90% reliability with a 120 MPa alternating stress on an 80 MPa mean stress:

Endurance limit                        280.5 MPa
Static yield safety factor                2.9
Fatigue safety factor                   1.839

Method: Fatigue analysis by endurance limit and mean-stress criterion
Formula: Se' = 0.5 Sut for steel, Se = ka kb kc kd ke kf Se', 1/n = sigma_a/Se + sigma_m/Sut
References:
  - Shigley's Mechanical Engineering Design (Tenth edition, 2015)

A call to unit_convert with a torque-to-energy request fails safely:

Error: Category mismatch: N·m is torque, J is energy.
Use a unit of the same quantity.

A call to unit_convert for a 100 cP lubricant converts to the SI unit:

Converted value                       0.1 Pa·s
  Value of 100 cP expressed in Pa·s.
  Value of 100 cP in the SI base unit Pa·s.
Factor: 0.001 (dynamic viscosity)

A call to unit_convert for copper with 401 W/(m·K) converts to the imperial unit:

Converted value                       231.7 BTU/(ft·h·°F)
  Value of 401 W/(m·K) expressed in BTU/(ft·h·°F).
  Value of 401 W/(m·K) in the SI base unit W/(m·K).
Factor: 1 (thermal conductivity)

A call to section_catalog for the HEB series returns the published sections:

Rows:
  - HEB 100 | h 100 mm | I 450 cm4 | W 89.9 cm3 | 20.4 kg/m | dims en-10365 | props arcelormittal-sections
  - HEB 120 | h 120 mm | I 864 cm4 | W 144 cm3 | 26.7 kg/m | dims en-10365 | props arcelormittal-sections
  - HEB 140 | h 140 mm | I 1509 cm4 | W 216 cm3 | 33.7 kg/m
  - HEB 160 | h 160 mm | I 2492 cm4 | W 311 cm3 | 42.6 kg/m

Method: Standard section catalog lookup
References:
  - EN 10365 - Hot rolled steel channels, I and H sections - Dimensions and masses
  - European sections - dimensions and section properties

Pass a catalog designation to beam_bending to use the published section properties:

Maximum bending moment                   15 kN·m
Maximum bending stress                26.93 MPa
Maximum deflection                   0.6411 mm
Bending safety factor                 13.18

References:
  - Roark's Formulas for Stress and Strain (Eighth edition, 2011)
  - Mechanics of Materials (Euler-Bernoulli beam theory)
  - EN 10365 - Hot rolled steel channels, I and H sections - Dimensions and masses
  - European sections - dimensions and section properties

A call to tolerance_stack compares a housing and shaft dimension:

Nominal stack                         1 mm
Worst-case lower bound              0.8 mm
Worst-case upper bound              1.2 mm
RSS lower bound                  0.8586 mm
RSS upper bound                  1.141 mm

Method: Linear dimensional tolerance stack
References:
  - Dimensioning and Tolerancing (ASME Y14.5-2018)
Warnings:
  - Worst-case bounds assume every dimension reaches its limiting value at the same time.
  - Independent RSS bounds assume zero-mean, independent variation. They are not guaranteed limits.

A call to shaft_load_cases compares bending and torque cases on a 50 mm shoulder:

Governing section index                   1
Governing load case index                 2
Governing von Mises stress            45.92 MPa
Minimum yield safety factor             7.732

Rows:
  - peak_combined | section midspan | sigma_vm 45.92 MPa | SF 7.732 | ref shigley-2015

Method: Shaft combined bending and torsion load cases
References:
  - Shigley's Mechanical Engineering Design (McGraw-Hill Education, Tenth edition, 2015)
  - Roark's Formulas for Stress and Strain (McGraw-Hill Education, Eighth edition, 2011)
Warnings:
  - Plane-stress von Mises stress assumes zero axial load and elastic material behavior.
  - The comparison does not include stress concentrations, fatigue, or dynamic amplification.

In SSE mode, an initialize response uses this event format:

event: message
data: { "jsonrpc": "2.0", "id": 1, "result": ... }

The same tools run over HTTP. Start the server with --transport http, then start a session with curl:

curl -s -D - http://127.0.0.1:3000/mcp \
  -H "content-type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-11-25","capabilities":{},"clientInfo":{"name":"curl","version":"1.0"}}}'

The response carries the session id in the Mcp-Session-Id header. Send that header on every later request:

curl -s http://127.0.0.1:3000/mcp \
  -H "content-type: application/json" \
  -H "mcp-session-id: <session id>" \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}'

See docs/transport.md for the full HTTP reference.

Development

Test status

The test suite is deterministic and offline. It covers the engines, the unit layer, the database, the tools, the catalog data, and the HTTP transport.

• The suite covers deterministic fixtures for 15 MCP tools across 18 test files.

• The CI matrix tests Node 22 and Node 24.

• The HTTP tests run a real server on an ephemeral port. They complete the full handshake over a real TCP connection. They cover JSON and Server-Sent Events responses.

• The CI workflow runs typecheck, tests, build, demo, a package check, and the HTTP smoke check.

• The CI workflow verifies the CLI contract over standard output.

• The CI workflow verifies both transport modes.

• Local verification passed for typecheck, build, CLI checks, shaft load-case tests, and the full test suite on the development host.

Run npm test to reproduce the results.

Limitations

• The beam theory applies to small elastic deflections.

• The material table covers common engineering grades only.

• The bolt tables cover coarse metric threads from M5 to M36.

• The bearing factors are typical values for deep-groove ball bearings.

• The critical speed is a first-mode approximation.

• The spring design covers static round-wire springs only. It does not estimate fatigue life for cyclic loads. Use the fatigue_analysis tool for a separate cyclic-load check.

• The fatigue analysis estimates the endurance limit for steel only. The tool applies to infinite-life design and does not model finite-life crack growth. Surface and reliability factors follow the standard table values.

• The press-fit theory assumes elastic material behavior and uniform friction. It does not model residual stress after yield.

• The section catalog covers common IPE, HEA, HEB, and UPN sizes. It does not include every size in the standard.

• The viscosity and thermal conductivity units cover common engineering units. They do not cover every named unit in older texts.

• The HTTP transport binds to the local host by default. Authentication is optional. Set ENGINEER_MCP_AUTH_TOKEN before a protected deployment.

• Browser clients need an explicit origin allow-list. Set ENGINEER_MCP_ALLOWED_ORIGINS with comma-separated origins. The transport does not provide TLS. Use a reverse proxy for public deployment.

• The HTTP transport keeps session state in memory. A restart clears every active session.

• SSE responses are not stored for reconnect. The server does not configure an event store.

• The built-in SQLite module of Node.js is still experimental.

• HTTP sessions stay in memory and do not survive a process restart.

• HTTP has no built-in authentication or TLS termination. Put it behind a trusted gateway.

• HTTP accepts request bodies up to 1 MiB.

• The tolerance stack models linear dimensions only. It does not model geometric tolerancing, correlation, angular errors, or Monte Carlo distributions.

• The shaft load-case tool models round sections with plane-stress von Mises stress. It does not model axial load, fatigue, keyways, or stress concentrations.

Check the cited sources for exact values.

Roadmap

Read ROADMAP.md for completed milestones, acceptance criteria, verification commands, and future work.

EngineerKit

Engineer MCP is part of the EngineerKit family. The family shares conventions for calculations, units, and provenance. Other EngineerKit servers can import @engineerkit/engineer-mcp/engine and @engineerkit/engineer-mcp/units. Read the boundary rules in docs/integration.md.

License

MIT. See LICENSE.