Best offer on record: Square Sandbox (free test environment). 4 verified findings, checked 2026-10-22.
Offers
Square Sandbox (free test environment) high confidence
The Square developer docs describe the Sandbox as 'a free, isolated server environment' at base URL https://connect.squareupsandbox.com, provisioned per application in the Developer Console. The page states: 'Use of the Sandbox environment is free of charge' and you can make 'an unlimited number of free Sandbox API calls.' Cards are never charged ('payments are never actually processed by a live bank'), and the Sandbox 'doesn't accept real credit cards or payment methods' — you use designated test card numbers/tokens. Functional limits: up to 10 additional test accounts beyond the default; Square hardware (POS terminals) not usable; Square for Restaurants, POS, Invoices, Snippets, Sites and Reader SDK are unsupported in the Sandbox; the Sandbox dashboard lacks receipts, refunds issuance, email, and banking features; real PII must not be stored in Sandbox.
Eligibility
Open to any Square developer: create a free Square account, register an app in the Developer Console, and the Sandbox is provisioned for that app. No .edu email, no startup age/funding cap, and no credit card required. Region: docs are US-oriented (developer.squareup.com); sandbox availability not region-gated in the docs I read.
How to claim
Sign up at squareup.com, create a Square account and an app in the Developer Console (developer.squareup.com), then use the sandbox base URL (connect.squareupsandbox.com) with test card values — no credit card or live seller account needed; sandbox API calls are free and unlimited.
Expiry
No expiration, time limit, or sunset date is documented for Sandbox access as of 2026-10-22; 'unlimited free Sandbox API calls' per the docs.
Gotchas
Trial-vs-free gotcha: the Sandbox is permanently free, but moving to production (live mode) is NOT free — in live mode cards are actually charged by a live bank and Square's pay-per-transaction processing fees apply (context: ~2.9% + 30c per card via the payments APIs; ACH per transfer). No hardware in Sandbox; several product lines unsupported; must not store real PII; test disputes/sandbox entities are invisible in the Developer Console or Dashboard.
Free developer access — no monthly/annual developer fees, no per-API-call fee advertised (pay-per-transaction live model) high confidence
Square's developer platform has no advertised monthly/annual developer subscription and no per-API-call charge. The Square pricing page leads with 'Your complete business toolkit, starting at $0' and 'Only pay when you take a payment.' The developer landing page (developer.squareup.com) and docs hub make no cost claim beyond that; the Get Started flow is 'Create an account and make your first Square API call in minutes.' No trial credits, no prepaid credit pool, and no developer-tier free-usage bucket exist on any page I could read (2025-2026 changes could not be checked via search — search budget exhausted this session).
Eligibility
Open to all developers/merchants who sign up at squareup.com (developer signup routes to app.squareup.com/signup?v=developers). No .edu requirement, no startup age or funding cap, no credit card required for account or app creation. Not a student-only or startup-only offer; it is the default model for everyone.
How to claim
Sign up free at squareup.com, create an app in the Developer Console, build and test in the free Sandbox; going live costs only standard per-transaction processing fees on payments you take (context: 2.9% + 30c online card; ACH per transfer) — no platform fee and no card required to sign up.
Expiry
No expiry; standing pricing model as displayed on 2026-10-22. Exact live-mode rates were not numerically confirmed on the page (rates render via JavaScript); the 2.9% + 30c figure is from task context, not re-verified today.
Gotchas
The $0 entry point covers software/toolkit ('Square Free' plan: POS app, online site, item library, invoicing, booking, checking & savings accounts, $0/mo); processing fees on live payments are separate and are the real cost. 'Plus' plan is a paid tier with 'lower processing fees' and a rendered 'Try free for N days' trial button (day count not rendered in the page text) — a trial, not a free tier.
Square 'Free' plan (the $0 software plan) — not student/startup-specific high confidence
On squareup.com/us/en/pricing, 'Square Free' starts at $0 and includes: 'POS app for any payment', 'Online site' (ordering profile, basic website, or booking site), 'Item library', 'Invoicing', 'Booking', and 'Checking and savings accounts'. Page states 'Only pay when you take a payment' and 'No hidden fees or locked-in contracts. Cancel or switch anytime.' A second specific number on the page: for Plus text marketing, 'The first 500 texts are free, then pay 3¢ per text.'
Eligibility
Any business/seller; no .edu email, no startup age/funding cap, no credit-card requirement stated for the free plan itself. Available generally, not a student or startup program.
How to claim
Sign up for Square at no monthly cost and use the included POS app, online site, invoicing, booking, and banking features for $0/mo; you only pay per-transaction processing fees when you take payments.
Expiry
No stated end date; 'Cancel or switch anytime' per the page, so no lock-in. Verified 2026-10-22.
Gotchas
This is a merchant-softwar plan, not a developer tier; 'free' excludes card/ACH processing fees on live payments, which are the main cost of the platform. The paid 'Plus' tier can undercut Free on processing rates but is a subscription — do not conflate the $0 plan with Plus's 'lower processing fees' perk.
Square App Partner Program — free open base tier; selective enhanced tier (no startup-only perks found) high confidence
The App Partner program (squareup.com/us/en/partnerships/app-partner) lets developers build and publish on the Square App Marketplace ('3.4 million views' cited). Base participation appears free and open: 'Don't wait on us to get started — dive into building, launch your integration, and reach out once it's live.' Even a declined enhanced-tier application leaves you free to 'build with our open platform.' The enhanced tier requires a form (personal/company details, Square App ID, industry, target markets AU/CA/FR/IE/JP/GB/ES/US, customer counts, app description) and is explicitly selective. Benefits of the enhanced tier: dedicated partner manager, 'profit-share eligibility' ('Create new revenue streams by sharing in profit generated through the app partnership' — no percentages, minimums, or fee structure disclosed), and co-marketing/sales enablement. No startup-only discounts, grants, or accelerated review appear anywhere on the page.
Eligibility
Open base tier: any developer who registers an app; no .edu email, no startup age or funding cap, no credit card required. Enhanced tier: application-based and selective, favoring 'highest impact' apps with 'strong enough demand'; target markets limited to AU, CA, FR, IE, JP, GB, ES, US.
How to claim
Build and publish your Square app for free (no fee to list), then apply via the app-partner form for the enhanced tier with a dedicated partner manager and profit-share eligibility.
Expiry
No expiry stated for base participation; enhanced-tier terms are individually negotiated. Verified 2026-10-22.
Gotchas
'Profit-share eligibility' is an opportunity, not a guarantee, with no disclosed percentages or fees — do not treat it as free money. The program is selective; rejection from the enhanced tier does not revoke free access to the open platform. No student-specific or startup-specific benefit was found on the page or the partnerships hub.
No student- or startup-specific free offer exists for Square Developer as of 2026-10-22: no .edu education license, no startup credit pool, no trial credits, and no startup age/funding-capped program were found on developer.squareup.com, the Square pricing page, or the partnerships hub (us/en/partnerships lists only App Partner and Developer Platform tracks; no education, reseller, or startup programs). Square's free offers are model-based and open to everyone (free Sandbox; no developer subscription; $0 'Square Free' software plan; free app-marketplace base tier), so nothing appears to have been sunset in 2025-2026 under a student/startup name. Caveats: (1) WebSearch was unavailable for this session (budget exhausted), so 2025-2026 change announcements (e.g., news of rate changes like the 2.9%+30c figure, which the pricing page renders via JS and could not be numerically re-confirmed) could not be independently checked; rate-level claims are carried from task context, not re-verified today. (2) Square Plus carries a 'Try free for N days' trial button whose day count is a template variable and did not render — a trial, not a free tier, and not student/startup-scoped.