StructureCalcs API
The same solver that powers the site — solve beams and trusses, query 2,600+ steel sections, and render diagrams, over HTTP. Built for AI assistants, engineers, students, and institutions.
Quickstart
Loads: negative = downward. A gravity UDL is start: -10 — the one convention to know before your first call. Below: a complete, working call — a 6 m simply supported beam under a 10 kN/m UDL. No key required; the free anonymous tier answers immediately. The same engine powers the site — how the numbers are verified.
curl -X POST https://api.structurecalcs.com/v1/beam/solve \
-H 'Content-Type: application/json' \
-d '{
"units": "SI",
"spans": [{ "length": 6, "E": 200, "I": 1e8 }],
"supports": [{ "type": "pin", "position": 0 },
{ "type": "roller", "position": 6 }],
"loads": [{ "type": "udl", "start": -10, "from": 0, "to": 6 }]
}'Response
{
"reactions": [
{ "type": "pin", "position": 0, "vertical": 30, "moment": 0 },
{ "type": "roller", "position": 6, "vertical": 30, "moment": 0 }
],
"extremes": {
"moment": { "maxSagging": { "value": 45, "position": 3 }, ... },
"deflection": { "max": { "value": -8.44, "position": 3 } }
},
"meta": { "engineVersion": "0.1.0+…", "units": "SI", "computeMs": 1 }
}Pricing
Published, flat prices — no per-call metering. The free tier works in ten seconds with no signup and no identity checks. Every result is verified against classical hand calculations, and there is an MCP endpoint for AI assistants.
How limits work. Three windows, all UTC: a per-minute burst, a per-day cap (anonymous only), and a per-month cap. Each resets on its own boundary — the next minute, midnight UTC, the 1st of the month. Exceeding any one answers 429, naming the window it hit in both the detail and X-RateLimit-Window, with a Retry-After for that window; solve responses carry X-RateLimit-Remaining. Your API key is your account — there is no login or password.
| Tier | Price | Includes | |
|---|---|---|---|
| Anonymous | Free | 30/day · 300/month · 10/min. Try it instantly, no signup. Shared per IP address. | Nothing to do — start calling. |
| Student | Free | 2,000/month · 60/min. For students, learning, and evaluation.Your own budget — the anonymous tier is shared per IP, so on a campus or office network it is consumed by whoever else is on it. | Request a key |
| Pro | $19/mo | 50,000/month · 300/min. For commercial projects — includes diagram rendering. | |
| Consultancy | $79/mo | 250,000/month · 600/min. Team use for a practice or consultancy. | |
| Institution | $499/yr | 100,000/month · 600/min. A yearly site licence for a school or department. | |
| AI / Enterprise | $499/mo | 1,000,000/month · 1,200/min. For AI assistants and platforms calling at scale, plus custom volumes. |
Student keys are issued by hand, usually within a day.
How paying works
Choose a paid tier and click Subscribe. You pay on a Stripe page in your browser — never in your terminal or code — and your key appears immediately afterwards, shown once. No card details ever touch this API. You can manage or cancel any time through Stripe’s customer portal — there is no separate login. Lost the tab, or lost your key? Go to your account page and we’ll email you a secure link to manage billing or re-issue your key.
Student keys stay by request (they are free), and the anonymous tier needs nothing at all.
Frequently asked questions
- Does StructureCalcs have an API and is it REST?
- Yes. StructureCalcs has a public REST API at api.structurecalcs.com that runs the same solver as the website over HTTP. You POST JSON to endpoints like /v1/beam/solve and /v1/truss/solve, and GET endpoints serve the steel-section library and standards; there is also /v1/health and the OpenAPI 3.1 spec at /v1/openapi.json. Interactive reference docs and copy-paste curl, Python, and JavaScript quickstarts live on the /api page.
- Is there an MCP server for StructureCalcs so AI assistants can solve beams, trusses and frames?
- Yes. There is a stateless MCP server at https://api.structurecalcs.com/mcp that speaks JSON-RPC over HTTP. It exposes nine tools: solve_beam, solve_truss, solve_frame, section_properties, get_section, search_sections, render_beam_diagram, render_truss_diagram, and render_frame_diagram. You can add it to Claude Code with "claude mcp add --transport http structurecalcs https://api.structurecalcs.com/mcp", or paste the URL as a custom connector in Claude.ai.
- What can I solve and render through the StructureCalcs API?
- You can solve multi-span beams (point loads, uniform and linearly-varying distributed loads — which cover triangular and trapezoidal shapes — pressure/area loads, and applied moments, returning reactions plus shear, moment, rotation, and deflection with their extremes), solve 2-D pin-jointed trusses (member forces, reactions, support settlement, thermal and fabrication effects), query all 2,600+ steel sections across the six standards, and render beam or truss diagrams. Diagrams are returned as SVG. There is no PDF, PNG, or report-builder endpoint in the current version.
- Is the StructureCalcs API free, and what does it cost?
- There is a free anonymous tier that works with no signup, capped at 30 requests per day and 300 per month per IP address with a 10-per-minute burst. A free Student key raises that to 2,000 requests per month. Paid tiers are Pro at $19/month, Consultancy at $79/month, Institution at $499/year, and AI/Enterprise at $499/month; pricing is flat, not metered. Paid tiers are self-serve: click Subscribe on the pricing table, pay by card on Stripe, and your key is shown once — manage or cancel any time in the Stripe billing portal.
- How do I authenticate with the StructureCalcs API?
- No authentication is needed for the free anonymous tier — you can start calling immediately. For higher limits you send your key as an HTTP header, Authorization: Bearer sc_live_..., and that key is your whole account (there is no login or password). A paid key is issued the moment you subscribe and pay on Stripe; a free Student key is issued by hand after you request one.
- What units and sign conventions does the StructureCalcs API use?
- Each request can set units to either SI (m, kN, kN/m, GPa, mm4) or imperial (ft, kip, k/ft, ksi, in4), matching the website’s conventions; SI is the default if you omit the field. The one sign rule to know is that loads are negative for downward, so a gravity UDL uses start: -10; support settlements are also negative for downward, and truss member forces come back tension-positive and compression-negative.
API Reference
The full contract — every endpoint, schema, and error — generated from the OpenAPI 3.1 spec.
Terms of use
By using the StructureCalcs API you agree to these terms, together with the site’s Terms of Use and Privacy Policy.
- Acceptable use. Use the API for its intended purpose — solving structural models, querying the steel-section library, and rendering diagrams. Do not attempt to overload it, work around the rate limits, resell raw access, or use it to operate a competing hosted solver.
- No warranty; not a substitute for engineering judgement. Results are provided “as is”, without warranty of any kind. The API is a calculation tool — a qualified engineer remains responsible for reviewing and signing off any design.
- Limits and tiers may change. Rate limits, quotas, tier definitions, and pricing may change with reasonable notice as the service evolves.
- Keys may be revoked. API keys that abuse the service — circumventing limits, disrupting availability, or breaching these terms — may be throttled or revoked.
Questions? Contact us.