| Order book depth | Depth at ±1/2/5/10 bps on target pairs, book resilience after sweeps, slippage vs size. Ask for historical depth and volatility snapshots. | Depth collapses in volatility, frequent gaps, no transparency or inability to provide basic depth analytics. |
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| Spread stability | Median and tail spreads (p90/p95), spread widening during stress, spread vs volatility. Ask about circuit breakers and price bands. | Spreads blow out without clear market cause, opaque halts, inconsistent post-only behavior in fast markets. |
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| Matching behavior | Priority rules (price-time), order type semantics (post-only, IOC/FOK), self-trade prevention, modify queue rules. Confirm any exceptions. | Undocumented exceptions, unpredictable queue behavior, post-only occasionally taking liquidity unexpectedly. |
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| Market data reliability | WebSocket latency and jitter, sequencing and gap detection, resync procedure, completeness. Ask for documented snapshot + delta workflow. | No sequence numbers, frequent disconnects, stale books, trade prints not aligning with book updates. |
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| API limits and errors | Rate limits (steady and burst), penalties, determinism of error codes, retry and idempotency guidance. Confirm institutional limit increases. | Random throttling, ambiguous errors, bans under load, no clear retry guidance. |
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| Cancel and reject behavior | Cancel latency, cancel acknowledgments, reject reasons distribution, reconnect order state. Test place, modify, cancel under load. | Cancels acknowledged but orders still trade, high rejects without actionable codes, unclear post-reconnect order state. |
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| Risk controls | Exposure limits, kill switch, price bands, sub-accounts, scoped API permissions. Ask if controls are self-serve and real-time. | No kill switch, slow manual interventions, all-or-nothing API permissions. |
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| Fees and rebates | Maker/taker tiers, rebate eligibility, volume attribution, billing accuracy. Ask for examples and edge-case fee treatment. | Fee logic does not match published schedule, frequent changes without notice, hidden add-on costs. |
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| Margin and collateral | Eligible collateral and haircuts, cross vs isolated margin, liquidation logic, risk model clarity, portfolio offsets if applicable. | Opaque liquidation rules, sudden haircut or eligibility changes, unpredictable margin jumps. |
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| Custody and security | Custody model, asset segregation, withdrawal controls (whitelists, multi-approver), audits or certifications under NDA. | Unclear custody model, weak withdrawal controls, unwillingness to share any security posture even under NDA. |
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| Compliance and KYB | Contracting entity, licensing posture by region, KYB requirements and timeline, monitoring and reporting support. | Unclear entity and regulatory answers, endless onboarding, unexplained freezes or restrictions. |
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| Support and escalation | Dedicated coverage, 24/7 escalation channel, incident comms, maintenance and symbol-change notices, response SLAs. | Retail-only support, no escalation path, slow incident response, breaking changes without notice. |
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