> ## Documentation Index > Fetch the complete documentation index at: https://docs.trdrs.co/llms.txt > Use this file to discover all available pages before exploring further. # Preview order margin > Returns the buying-power impact of a hypothetical order. The call is read-only: it never places an order, so it carries no `clientOrderId` (no idempotency key) and is not risk-gated. `estimate` is `false` on brokers that compute the figure for real (a TastyTrade dry-run) and `true` otherwise; `marginRequired` is null when unknown. ## OpenAPI ````yaml /partner-platform/openapi.json post /api/trading/margin-preview openapi: 3.1.0 info: title: trdrs Engine API version: 1.1.0 description: >- ## API Reference This is the served OpenAPI contract for the trdrs engine: market data, trading and account routes for your firm's traders, trdrs Connect account-registration handoff, and preview challenge routes. See Quick Start for the first integration path: key setup, market config, chart data, Connect account registrations, idempotency, stream reconnects, and conformance. See Overview and API Standards for the cross-cutting contract rules. servers: - url: https://app.trdrs.co description: Production - url: / description: This engine security: [] tags: - name: Market data description: >- Symbol search and resolution, OHLCV history, quote snapshots, the server clock, and the live bar stream. Crypto rides each venue’s public feed; futures stream from the caller’s own connected Rithmic account. With none connected, futures requests answer 503 `feed_requires_connection`. - name: News description: >- Aggregated market news and the economic calendar, from licensed/open sources, keyword-tagged with futures roots at ingest. Platform-wide content (nothing per-user), admitted exactly like Market data: a licensed origin, a session, or a firm API key. Headlines page by published time, scope by instrument root, and stream live over SSE; thumbnails serve through the image proxy. - name: Trading description: >- The money surface: entries, exits, replaces, cancels, and position/account flattening. Every order-placing call uses `clientOrderId` as its idempotency key. - name: Account description: >- Reading a connected account. You do not create trading accounts here: a trader connects their own broker account (or creates a free demo account) in the app, and firms create evaluation accounts through the Partner API (Firm accounts → Create evaluation accounts) or register venue accounts through Connect (Create an account registration). Account state and the durable ledgers: balances, positions, working orders, fills, P&L history, and the live account stream. - name: Connect description: >- trdrs Connect account registration, for partner firms. Register an account you issued on your own venue — a pending account registration — with the trader’s sign-in email, optionally the venue account id and the login name your venue issued. The trader finds it waiting in the connect flow the moment they sign in with that email: the connect step is pre-filled with everything except the credential, which the trader always enters themselves. A registration never transmits a password and never grants access to anything before the trader’s own login succeeds. These routes answer a partner-scoped key only; a firm API key or a user session gets 401. Registrations expire after 30 days; re-registering the same email + account refreshes the expiry instead of duplicating. The end-to-end flow guide is **[Quick Start](/docs/guides/quick-start)**. - name: Firm accounts description: >- Evaluation accounts your firm issues on the trdrs venue, through your partner key — the other half of account setup. Connect registrations hand off accounts that exist on your venue; these routes create and manage accounts on ours: the trader trades them on trdrs, and your firm owns the lifecycle. Every route is scoped to accounts your firm created through this API — an account the same trader opened themselves is invisible and untouchable here, by construction. Creation is batched with per-item results, and every write carries your own `referenceId`, so a crashed pipeline retries safely. Served when the deployment runs the prop engine; without it, every route in this group answers `404`. - name: Webhooks description: >- The outbound event bus: register an https endpoint and the platform pushes events to it instead of your back office polling us. Every delivery is signed (`trdrs-signature: t=,v1=` over `${t}.${rawBody}`) so you can prove it came from us and is fresh, and every delivery is durable — a failed attempt is retried with backoff for about nine hours and the whole log is readable, so an endpoint that was down is a delay rather than a lost event. Serves brokers and prop firms alike: the account-registration (`registration.*`) events fire wherever Connect does, and the account events fire where the prop engine runs. - name: Challenges description: >- The prop evaluation surface: challenge programs and a trader’s own enrollments. **Preview: the one group on this page outside the additive-only guarantee** (the pre-contract v1 scaffold; the Phase-1 rebuild will change these shapes; see Stability). **Cookie-authenticated, not key-authenticated**, and served only when the engine runs with `CHALLENGES_ENABLED`; without that flag the bundle is absent and every route below returns `404`. The firm-console/admin half of this surface is deliberately not documented here. It is back office, not licensed surface. paths: /api/trading/margin-preview: post: tags: - Trading summary: Preview order margin description: >- Returns the buying-power impact of a hypothetical order. The call is read-only: it never places an order, so it carries no `clientOrderId` (no idempotency key) and is not risk-gated. `estimate` is `false` on brokers that compute the figure for real (a TastyTrade dry-run) and `true` otherwise; `marginRequired` is null when unknown. parameters: - name: broker in: query schema: type: string description: >- Pick a connected broker. Omitted = the priority default. A present-but-unknown value is a 400, never a silent fallback. - name: account in: query schema: type: string description: >- Pick an account within that broker. Validated against the caller's own set; out-of-set is a 400. requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/MarginPreviewRequest' responses: '200': description: The preview content: application/json: schema: $ref: '#/components/schemas/MarginPreviewResponse' '400': description: >- Invalid instrument/side/qty/orderType, or an asset class this broker cannot route (carries a machine `code`) content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '401': description: Missing/unknown/revoked credential content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - tenantKey: [] x-codeSamples: - lang: javascript label: TypeScript source: >- const res = await fetch('https://app.trdrs.co/api/trading/margin-preview', { method: 'POST', headers: { 'content-type': 'application/json', Authorization: `Bearer ${process.env.TRDRS_API_KEY}`, }, body: JSON.stringify({ "instrument": "ESU6", "side": "buy", "qty": 2, "orderType": "market" }), }) const data = await res.json() - lang: shell label: cURL source: |- curl -X POST 'https://app.trdrs.co/api/trading/margin-preview' \ -H "Authorization: Bearer $TRDRS_API_KEY" \ -H 'content-type: application/json' \ -d '{"instrument":"ESU6","side":"buy","qty":2,"orderType":"market"}' components: schemas: MarginPreviewRequest: type: object properties: instrument: type: string side: type: string enum: - buy - sell qty: type: number orderType: type: string description: Defaults to `market`. limitPrice: type: number triggerPrice: type: number required: - instrument - side - qty example: instrument: ESU6 side: buy qty: 2 orderType: market MarginPreviewResponse: type: object properties: marginRequired: type: - number - 'null' estimate: type: boolean currency: type: string sufficient: type: - boolean - 'null' required: - marginRequired - estimate - currency - sufficient example: marginRequired: 3080 estimate: true currency: USD sufficient: true ErrorResponse: type: object properties: error: type: string required: - error example: error: invalid_instrument securitySchemes: tenantKey: type: http scheme: bearer description: >- Your firm’s API key (the API calls this the `tenant` key; `trdrs_sk_…`), server-to-server only. ````