When an agent calls a Surety carrier to ask how a bond was priced, the answer often begins with someone opening a spreadsheet. As Destry Gustin, Product Lead at Tinubu, describes it: "Even when there is confidence in the calculation, you often have to pull out a calculator and do the math right there, reverse engineering how the system might have come up with those rates. That's how many carriers do it today."
Tinubu's rebuilt Rating Engine is designed to make that workaround unnecessary, while vastly expanding Surety underwriting and bond management capabilities. Released as part of Tinubu's ongoing platform modernization, it delivers real-time calculation, full visibility into how every premium is derived, and expanded capabilities for complex contract business — all on an API-first architecture.
Building on Decades of Industry Knowledge and Customer Feedback
The Rating Engine touches every part of the bond lifecycle. A mistake at the point of calculation flows downstream into incorrect documents, failed compliance checks, and reporting that doesn't reflect the actual book. Getting it right consistently across bond types, territories, and transaction events is harder than it looks.
As Gustin says, it requires "deep, accumulated knowledge of legislative requirements, municipal tax structures, reporting rules, and the particular ways different territories manage bonds." Tinubu has been building and refining that knowledge for over 20 years, and all of it is embedded in the new engine.
"We used an API-first methodology on this, so it's a scalable solution," says Gustin. Rather than update the existing Rating Engine, Tinubu rebuilt it on a new technology foundation designed for the operational demands carriers have today and the ones they'll have going forward.
The new engine also responds to a wide range of customer feedback, including features carriers wanted to add and some they wanted to reduce. "Our previous Rating Engine allowed you to make modifications to everything during a flat cancellation," says Gustin. "Customers told us this was causing complications, so they wanted the premium, commissions, and everything reset back to zero. That's what we implemented."
There is now a clean reset, with no room for ad hoc adjustments that could leave financial records in an ambiguous state. In general, though, "carriers wanted additional flexibility," notes Gustin, and the new Rating Engine delivers it.
Full Transparency
"A very common question carriers get from agents, or want to answer internally, is 'why did it get rated at this? Why is my commission calculating at X? How did this change between each transaction on the bond?'" says Gustin.
"In most of today's systems, it's kind of a black box. You put data in, and you expect the right results to come out. Our rating solution lets you look at any bond and see every piece of data that went into the calculation, including why a commission is calculated a particular way or how a premium changed between transactions. It's all visible in real time."
For any carrier with agents logging into the system, agents see it too. That alone reduces inbound queries: when an agent can see the full calculation, they rarely need to ask.
A persistent problem with earlier systems was that applying overrides could overwrite the original rate context, leaving no way to see what the baseline had been or who had changed what. The rebuilt engine solves this through rating persistence.
When a bond is finalized, a snapshot of all rates is captured. Every subsequent transaction (adjustment, renewal, cancellation) works from that preserved record. Overrides sit on top of it; removing one restores the original calculation instantly. Every component of a premium is a separate, visible line item: base premium, modifiers, surcharges, commissions, fees, and taxes. Nothing is destructive; everything is auditable, including a full log of who made changes, when, and why.
Transparency extends downstream via APIs. The rebuilt engine exposes over a hundred data elements, in line with the platform's broader push toward real-time data connectivity. Where a downstream billing or accounting system previously received only a final premium figure, it can now receive every tier, modifier, and rate that produced that number. General ledgers, financial reporting tools, and compliance entities stay aligned without manual reconciliation, and the same pricing detail visible on screen is accessible via the TSBA Bond Data API.
Override Flexibility for Complex Business
"For small bonds that are high transaction, carriers want consistency in rating," says Gustin. "They want to be able to configure it and just have it automatically calculated. But for larger accounts, and contract bonds in particular, there will be a lot of per-bond adjustments, including adjusting rates based on risk for a specific project, or discounting an aspect of a large commercial bond."
The rebuilt engine supports this through configurable modifiers applied at any layer: tier amounts, tier rates, and total amounts for each premium component (base, maintenance, time surcharges, taxes, fees, and commission rates).
Three override modes reflect the situations underwriters actually face:
- A permanent override for a negotiated rate that becomes the new baseline for a client
- A version-only override for a one-off competitive discount that shouldn't carry forward
- An override for a rate adjustment that should be revisited at renewal rather than locked in.
"Carriers want to be able to change those amounts quickly," says Gustin. "The granularity combined with a simple interface that updates in real time is a powerful feature."
These expanded contract capabilities make it easier for carriers managing complex portfolios to do more of their work within Tinubu, streamlining workflows and helping them take fuller advantage of the rest of the platform.
Reducing Errors in the Active Workflow
As an underwriter or agent adjusts any field (effective dates, bond penalty amounts, expiry) the entire pricing structure recalculates on the spot. Catching an input error in the active workflow costs a fraction of what it costs to trace and correct after the fact.
The same principle applies downstream. Accounting and legal reporting software historically received a single lump-sum premium with no visibility into how it was determined. Now, individual tiers, modifiers, and rates flow through to external systems.
The Foundation Underneath the Highway
Further error reduction will come from how the new Rating Engine fits into Tinubu's fully connected platform, where carrier underwriting, broker submission, and AI-powered decisioning run as a single workflow.
"The concept of the digital highway is that a carrier's underwriting and rates are fully accessible to agents in real time," says Gustin. "The Rating Engine ensures agents are writing the way the carrier wants, and the highway delivers that to them. The days of an agent issuing a bond with incorrect rates or outside carrier guidelines are over."
The rebuilt Rating Engine underpins the rest of the platform. Pricing that is correct, transparent, and fully communicated to every system gives carriers, agents, and downstream teams a foundation they can trust.
Early Adoption
The rebuilt engine is already in use. Two anchor clients have been running it for the past month, and the reception has been positive. "I'm really happy to say that they're excited about the changes," says Gustin. "They have provided some additional feedback which we're incorporating as we speak, so that it's an even better product."
The rebuilt Rating Engine is part of a 2026 platform evolution that also includes BondImport.ai and the digital highway between TSBA and TSC. For carriers that have been reconciling premiums by hand, fielding agent queries with spreadsheets, and managing overrides without an audit trail, the new engine clears each of those obstacles — and gives underwriting teams back the time to focus on judgment, not arithmetic.
