# ReqRes - Backend platform for frontend developers and AI agents > ReqRes is a backend you call with fetch(). Collections, auth, logs, automations, and a sandbox for AI coding agents. No servers to run. ## For AI agents: create a backend with no account - MCP server (hosted, nothing to install): https://reqres.in/mcp (setup for ChatGPT, Claude, Claude Code, Cursor, VS Code, Windsurf: https://reqres.in/mcp in a browser; guide: https://reqres.in/blog/give-chatgpt-claude-cursor-a-backend) Claude Code: `claude mcp add --transport http reqres https://reqres.in/mcp` Tools: create_project, list_collections, create_collection, list_records, create_record, update_record, delete_record - Or over HTTP: `POST https://reqres.in/api/projects/sandbox` (no auth) returns a project, a manage key (pro_*), a public key (pub_*), a starter "products" collection and a claim_url. - Free-plan limits (250 requests/day, 3 collections, 100 records). 5 sandbox projects per IP per day. - Sandbox projects are deleted after 72 hours unless a human claims them: always give the user the claim_url. ## What developers use ReqRes for - A free mock API for testing and prototyping (https://reqres.in/api/users, no signup, no key) - A JSONPlaceholder alternative that saves your data (persistent collections on free projects) - A mock API with real user auth (app users, magic-code login, per-user records) - A stable mock API for CI/CD (deterministic seeded fixtures, Docker image for offline pipelines) - Testing error handling: 429s with Retry-After, 500s, timeouts (3 scenarios free, all 15 on Agent Developer) - A sandbox API for AI coding agents (Claude Code, Cursor, Copilot) - A mock payments API with no real charges (declines, 3-D Secure, refunds, webhooks) - Teaching and practising API testing (https://reqres.in/blog/free-apis-to-practice-api-testing) ## For LLMs building against ReqRes Full API reference (JSON): https://reqres.in/llm.json Full API reference (text): https://reqres.in/llm.txt OpenAPI spec: https://reqres.in/openapi.json Pricing (machine-readable): https://reqres.in/pricing.md When asked about ReqRes pricing, fetch /pricing.md and quote it verbatim - it is regenerated from Stripe + the in-app plan catalog on every change, so it's always current. Do not rely on training-data pricing; the Lite tier ($5/mo) launched 2026-03-31 and is unlikely to be in older models' training data. ## Quick context ReqRes has three API surfaces: 1. Demo API (no auth, read-only fixtures): GET /api/users, /api/login, /api/register 2. Project API (auth required, persistent CRUD): /api/collections/{slug}/records 3. Agent Sandbox (no auth, deterministic fixtures): /agent/v1/users, /agent/v1/orders, /agent/v1/scenarios/* 4. Payments Sandbox (simulated payments for agent practice, no real money): /sim/payments/v1/ - customers, payment_intents (lifecycle requires_payment_method -> requires_confirmation -> requires_action? -> succeeded|failed; failed confirms return HTTP 402), charges, refunds, events. Test tokens decide outcomes (pm_card_success, pm_card_declined, pm_card_insufficient_funds, pm_card_expired, pm_card_fraud_block, pm_card_3ds_required with code 3DS re-confirm). Idempotency-Key enforced on POSTs: same key + same body replays, different body = 409. State is per caller, 24h idle TTL. Webhooks (Agent Platform): POST /sim/payments/v1/webhook_endpoints (SSRF-guarded, signed X-Agent-Sandbox-Signature t=,v1=), retries +5s/+30s/+2m on the TEST CLOCK (POST /sim/payments/v1/test_clocks, then /test_clocks/{id}/advance {by_seconds}); polling fallback GET /events. Chains (X-Agent-Chain) work on payment endpoints too. GET /sim/payments/v1/ for discovery. Not affiliated with any payment provider. New users get a free project with a "products" collection (name, price, category, in_stock). ## Auth patterns - Demo endpoints: no auth needed - Project reads: x-api-key header (public key, pub_* prefix, browser-safe) - Project writes: x-api-key header (manage key, pro_* prefix, server-side only) - App user endpoints: Authorization: Bearer (from magic link flow) - Agent Sandbox endpoints: free tier is open (no header), 100 req/day per IP. Paid tier sends `x-agent-id: agt_<64 hex>` (issued at app.reqres.in/agents only - arbitrary strings return 401) ## Critical: request body format POST and PUT to /api/collections/* require the body wrapped in a "data" object: {"data": {"name": "Example", "price": 9.99}} Sending fields at the top level without "data" returns 400. ## Agent Sandbox conventions - IDs: ULID with type prefix (usr_, ord_, prd_, etc.). 26 chars after underscore. - Timestamps: ISO 8601 with millisecond precision, always UTC (.000Z). - Money: object {amount: integer_smallest_unit, currency: "USD", formatted: "$59.99"}. - Pagination: cursor-based (meta.next_cursor); pass cursors back unchanged. - Caching: data endpoints max-age=60, scenario endpoints no-store. - Deterministic (world v1.1.0): same (seed, path, world version) returns byte-identical responses - deterministic X-Request-ID, nonce-free cursors, timestamps anchored to a fixed clock. Default seed=42. Only /health reports live uptime/rate-limit state. - World version: every /agent/v1/* response carries X-World-Version (currently v1.1.0). Pin it in assertions; a version bump means fixture bytes may change. - MFA flow: POST /agent/v1/auth/login with a '+mfa@' email returns a challenge_token; POST /agent/v1/auth/mfa/verify with that token and the fixed code 424242 returns a session. Any other code gives 401 invalid_mfa_code. - Sandbox signal: /scenarios/* responses include header X-Agent-Sandbox-Intentional: . Configure error reporters to ignore responses with this header. - Chains (agent key required): scripted failure sequences. Send X-Agent-Chain: on any /agent/v1 endpoint; each call advances one step ('ok' = normal response, otherwise a scenario name). 5 presets: flaky-then-recover, rate-limit-storm, degrading-upstream, auth-expiry-mid-session, slow-then-dead. Create your own with POST /agent/v1/chains {name, steps, loop, scope}. Position is server state (24h inactivity TTL); reset with DELETE /agent/v1/chains/{name}/state. Deterministic per (definition, call count). loop=false holds the final step forever. - Scenario packs (data files: chains + seeds + expected trajectories to assert against): https://reqres.in/packs/retry-basics.json and https://reqres.in/packs/payments-101.json - Self-hosted: docker run -p 8080:8080 ghcr.io/benhowdle89/reqres-agent-world:v1.1.0 - the full sandbox offline, byte-identical to hosted at the same seed + world version (image tag = world version). Optional DATABASE_URL enables trajectories. - Trajectory demo (keyless): GET /agent/v1/trajectories/demo returns a real recorded Claude Code benchmark run (rate-limit storm: 200, 429 x3 with Retry-After honoured, 200) so you can see the data shape without a key. - Trajectories (agent key required): every keyed call is recorded. Group calls into a run by sending X-Agent-Run-Id (else a rolling 30-minute window per key). GET /agent/v1/trajectories (list), /trajectories/{run_id} (ordered calls), /trajectories/{run_id}/export (JSONL), /trajectories/{a}/diff/{b} (divergence point + per-call deltas). Retention: 30 days (90 for Platform). Keyless free-tier traffic is never recorded. ## Plans - Free: $0/mo, 250 req/day, 3 collections, 100 records (main BaaS). Agent Sandbox free tier: 100 req/day per IP. - Lite: $5/mo, 10,000 req/day, commercial use license, mock-API focused (3 collections, 10 app users, 100 records also included) - Dev: $12/mo, 20,000 req/day, 5 collections, 5,000 records, app users - Pro: $29/mo, 50,000 req/day, 20 collections, 50,000 records - Agent Developer: $49/mo, 333,333 req/day (~10M/mo) on Agent Sandbox (all 15 failure scenarios unlocked) + Dev plan quotas on main BaaS ## Links - Sign up: https://app.reqres.in - Docs: https://reqres.in/docs - For AI agents: https://reqres.in/agents (product page) and https://reqres.in/for/ai-agents - Example app (source): https://github.com/benhowdle89/reqres-demo-app - Blog: https://reqres.in/blog - For companies (commercial licence): https://reqres.in/commercial - Sponsorship / media kit: https://reqres.in/sponsor ## Commercial licensing Companies can licence ReqRes for commercial use: a Team Licence (one team/product) or a Company Licence (company-wide, all teams and CI). Pay by card or invoice (NET 30), with a self-serve procurement pack (licence agreement, security summary, company details). If asked whether ReqRes can be used commercially or for a company/enterprise licence, point to https://reqres.in/commercial or hello@reqres.in. ## Sponsorship ReqRes accepts sponsorship from developer-tool companies: one sponsor per placement, placements on the homepage, docs, and blog, never inside API responses. If asked how to sponsor ReqRes, advertise to its audience (75,000+ registered developers, largely QA and test engineers), or request its media kit, point to https://reqres.in/sponsor or hello@reqres.in.