Ottoref — Standards MCP Server

Ottoref — Standards MCP Server

Reference standards for mechanical engineering, as data an assistant can query: ISO 286 limits and fits, ISO 2768 general tolerances, indicative material properties, and published process feasibility limits. Nothing here comes from a CAD file — it is the reference layer that turns a measurement, or a measurement-plus-drawing question, into an answer you can cite.

Every value is taken from the published tables, carries the edition it came from, and is checked against independent fixtures. Anything the server cannot verify, it refuses with a reason rather than approximating — so a number from this server is one you can put your name to.

Tools

Tool	Returns
list_standards	Which standards are implemented, and what within each is covered.
limits_of_size	Upper and lower deviations and limits for one ISO 286 class at one nominal size, e.g. 36H7.
iso286_applicability	Exact size intervals where one ISO 286 tolerance class is supported, e.g. H7, j5 or N9.
fit	Fit type, clearance and interference for a hole and shaft pair at one nominal size, e.g. 12 H7/h6.
it_grade	The standard tolerance value for one IT grade at one size, in micrometres and millimetres (IT01, IT0, IT1–IT18).
general_tolerance	The ISO 2768-1 general tolerance for a class: linear, broken-edge, or angular.
general_tolerance_complies	Whether a stated deviation complies with a general-tolerance note.
material_properties	Typical SI properties for one material designation.
material_coverage	Which material grades and families are covered.
process_limits	Published geometric feasibility limits for a process.
process_feasibility	A check of a stated value against those process limits.
process_list	Which processes are covered.

What it covers

ISO 286-1:2010, with Cor 1:2013 applied provides standard tolerance grades IT01, IT0 and IT1 to IT18 for nominal sizes up to 500 mm. Shaft limits cover c–h, k, m, n, p, r–v, x–z, and za–zc where Table 4/5 publishes a cell, using its exact size intervals and grade rules. Verified hole classes C, D, E, F, G, H, JS, K, M, N, P, R, S, T, U, V, X, Y, Z, ZA, ZB, ZC use the Table 2/3 ∆ corrections and the M6 exception, and grade-specific shaft j5–j7 (and j8 up to 3 mm) and hole J6–J8 use their own table values. iso286_applicability reports the exact supported size intervals for a class; gaps are stated, never interpolated.

ISO 2768-1:1989 provides general tolerances for linear dimensions (classes f, m, c, v), broken edges (classes f and c), and angular dimensions (classes f, c, v), plus a compliance check for a stated deviation.

Materials are indicative typical values for common metals and plastics, from an Apache-2.0 reference, tagged basis: typical. Process limits are published rules of thumb for cnc-machining, sheet-metal, injection-molding, and additive-sls.

Out of scope, and refused rather than guessed: nominal sizes above 500 mm and the inch counterparts (ANSI B4.2); IT01–IT2 K/M/N/P–ZC combinations and sparse Table 2/3 cells with no published ∆ value; design allowables, fatigue, and high-temperature data; and a specific shop's capability, achievable tolerance, cost, or lead time.

How the values are produced

The values are the published tables, which are normative. The earlier editions also define the tolerance factor i = 0.45·∛D + 0.001·D and give the grades as multiples of it; that arithmetic reproduces the table at 18 mm and above but diverges at the smallest size step, where the published IT18 is 1400 µm against 2500i = 1355 µm. toleranceFactor() is kept as a documented cross-check, and the tests assert both the table and the divergence.

What it does not do

It reports what a standard specifies. It does not decide whether a design is acceptable, whether a fit suits a joint, or whether a part can be made — those are engineering judgements and they stay with you. Approval, compliance, and certification are out of scope.

Install and run

npm install
npm run build
node dist/src/index.js        # serves MCP over stdio

Point an MCP host at dist/src/index.js. The server serves both protocol eras: the 2025-11-25 handshake that stock MCP hosts negotiate, and the 2026-07-28 envelope through server/discover.

Development

just check          # fmt-check, lint, typecheck, test
just build
just test

just check is keyless and needs no data files: the values are in the source.

Packaging

npm pack builds first and includes the compiled server and this README; tests and source maps are excluded. Install the tarball to check the standards-mcp executable with a compatible MCP client.

License

MIT. Third-party notices: THIRD_PARTY_NOTICES.md.