How to Verify a Contractor License in California: CSLB Lookup Guide

Why an Altadena ADU Project Starts With a CSLB License Check

A six-figure ADU build in Altadena begins with a five-minute online search — not a handshake. Under California law, any home improvement job over $1,000 requires an active contractor license (a threshold raised from $500 effective January 1, 2025 under AB 2622), and every ADU project in Altadena will clear that line many times over.

The stakes go beyond legality. Homeowners who hire unlicensed contractors forfeit access to CSLB mediation, bond claims, and the Contractors Recovery Fund — the very protections that exist to make you whole when a build goes wrong. With an ADU investment often exceeding $200,000, that's a lot to leave on the table.

California's licensing system is run by the Contractors State License Board, which has regulated the trade since 1929 and currently licenses roughly 285,000 contractors across 45 classifications. For an ADU or garage conversion, the classification that matters is B — General Building, which covers additions, full remodels, and detached structures. A roofer (C-39) or electrician (C-10) may be excellent at their trade, but they can't legally pull permits for a complete ADU build.

The lookup itself is free and takes about five minutes at the CSLB's official site. Search by license number, business name, or personal name, then open the full detail page — the search results summary alone isn't enough. You're confirming four things before you sign anything:

• License status reads "Active" — an inactive or suspended license means the contractor cannot legally take on new permitted work
• The required $25,000 surety bond is on file
• Workers' compensation is current (or a valid exemption for a sole operator with no crew)
• The classification covers your scope of work, and the legal business name matches your contract

That last point matters more than most homeowners realize. A name mismatch between the CSLB record and the proposal is one of the most common scam patterns, often signaling a borrowed license. Contractors must display their license number on bids, contracts, and advertising — if one won't provide a number that checks out, treat it as a stop sign.

Here's what that verification looks like in practice. JMB Builders LLC, an Altadena-based general builder and the featured builder in our guide (a paid placement), holds CSLB license #1103479. Running that number through the official CSLB lookup lets you confirm status, bond, and classification yourself — which is exactly the habit we encourage for every builder you consider, including any recommended by Altadena ADU Builder.

One caution: verification isn't a one-time gate. A contractor who was active last month could be suspended today, so re-run the check before each payment milestone, not just before signing.

The Five-Minute CSLB Lookup: Step-by-Step Walkthrough

The whole verification process takes about five minutes on the official CSLB website, and it's free. The Check a License tool covers roughly 285,000 licensed contractors across 45 classifications, plus Home Improvement Salesperson registrations.

Start with the license number if you have it — it's the fastest search type. Contractors must display their CSLB number on bids, contracts, and advertising, so ask for it directly. If a contractor can't or won't provide one, treat that as a stop sign: a number that doesn't come up at all means the license is expired, cancelled, inactive, or was never issued.

You can also search by business name or personal name. Name searches return up to 25 matching licenses with city and status, which is useful when a contractor operates under a slightly different name than the one on their proposal.

Open the full detail page — the search results only show a summary. That detail page is where you confirm what matters:

• Status is "Active" — not expired, suspended, or inactive
• The $25,000 surety bond is on file
• Workers' compensation is current, or a valid exemption applies
• The classification covers your scope of work
• The legal business name matches your contract and insurance documents

That last point matters more than most homeowners realize. A name mismatch between the CSLB record and the paperwork in front of you is one of the most common scam patterns, often signaling a borrowed license. Classification matters too: ADUs and most residential work require a B — General Building license, and a specialist like a C-39 roofer can't legally pull permits for a full remodel.

Skip third-party lookup sites. They're slow to update — some cache CSLB data for 24 hours or refresh weekly — so a contractor who was active on an aggregator could already be suspended on the official record. A contractor who was active last month can be suspended today, so re-run the check before each payment, not just before signing.

For contractors who claim to be newly licensed, the CSLB also offers an application status check by Application Fee Number, personnel name, or business name. If the application is still pending, that contractor cannot legally contract for work yet.

As a worked example, JMB Builders LLC — the licensed Altadena general contractor featured on this site (paid placement, disclosed) — holds CSLB #1103479. Typing that number into the lookup brings up the detail page where you'd confirm Active status, the bond, and the B classification in seconds. That's exactly the exercise we recommend Altadena homeowners run on any builder before an ADU feasibility consultation, including ours.

What to Verify on the License Detail Page: The Five-Field Checklist

The search results page only gives you a summary — the license detail page is where the real verification happens. Before you sign anything, walk through five fields in order, and treat any single one that's off as a reason to stop signing.

• Status must read "Active." Inactive isn't automatically bad, but it means the contractor cannot legally contract for new work right now. A number that doesn't come up at all means the license is expired, cancelled, or never issued — a stop sign until the contractor provides one that checks out.
• Confirm the $25,000 surety bond is on file. Every licensed California contractor must carry one, but understand what it is: not insurance, rather a recovery mechanism that pays homeowners harmed by contractor misconduct.
• Check workers' compensation. It should be current, or a valid exemption if the contractor is a sole operator — but an exemption with a crew on site is a red flag, since a homeowner can become liable if a worker gets hurt.
• Verify the classification matches your scope. Class B General Building is what an ADU requires; a C-39 roofer, by contrast, can't legally pull permits for a full remodel.
• Match the legal business name on CSLB against your contract. A name mismatch is one of the most common scam patterns, often signaling a borrowed license.

You can model this using the featured Altadena builder on our guide, JMB Builders LLC (CSLB #1103479): run the number through the official CSLB lookup tool and confirm status, bond, and classification in about five minutes.

Beyond the five fields, read the license history and disciplinary sections. Long continuous history is a positive signal; a recent reissue after a gap deserves a follow-up question. Distinguish a single resolved citation from a pattern of recent disciplinary actions — and note that common suspension causes include failure to maintain workers' comp, unpaid bond claims, and unresolved citations. If you see a suspension, stop all work immediately and contact CSLB at 800-321-CSLB (2752).

One caveat: the lookup won't show resolved or dropped complaints, so a clean record is not proof of perfection. Supplement it with references and reviews, and remember that a contractor who was active last month could be suspended today — re-check the license before each payment, not just before signing. When you're ready to evaluate builders for your project, our free ADU feasibility consultation with a cost-quiz concept render can help you compare your options.

Red Flags, Limitations, and How to Read Between the Lines

A clean CSLB record is reassuring — but it is not the whole story. The lookup tells you whether a contractor is legal to hire; it cannot tell you whether they are good to work with.

The first stop sign is the simplest: no license number found at all. If a number does not come up in the CSLB system, the license is expired, cancelled, inactive, or was never issued — treat that as a hard stop until the contractor provides a number that checks out, per license verification guidance.

The second is a workers' comp exemption paired with a crew on site. If a worker gets hurt where an exempt contractor has employees on the ground, the homeowner can become liable, as contractor-run sources warn. The third is classification mismatch: a C-39 roofer, for example, cannot legally pull permits for a full kitchen or bath remodel. For an ADU, you want a Class B General Building contractor.

Here is the honest limitation: most consumer complaints never appear in the CSLB record because they are resolved or dropped, so a clean record is not proof of perfection. The lookup also says nothing about communication quality, change-order handling, schedule realism, or punch-list treatment.

That is why Altadena ADU Builder recommends supplementing any verification with:

• Three recent references you actually call
• A sample written estimate with itemized scope
• Payment milestones tied to inspection sign-offs
• A recent permit pulled under the contractor's exact legal name

California law caps your deposit at $1,000 or 10% of the contract price, whichever is less, under Business and Professions Code Section 7159, per verification guidance. A contractor asking for half the project upfront is breaking the rules before the work begins.

Verification is also not a one-time event. A contractor who was active last month could be suspended today — re-check the license status before each payment release, not just before signing. If something goes wrong mid-project, the CSLB complaint line is 800-321-CSLB (2752), and homeowners who hire unlicensed contractors lose access to CSLB mediation, bond claims, and the Contractors Recovery Fund.

If you are evaluating ADU builders in Altadena and want help applying these checks to real candidates, our free ADU feasibility consultation includes a cost quiz and a concept render so you can see the project before you commit to anyone.

Worked Example: Running a Real Altadena Builder Through the Lookup

Theory only gets you so far — so let's run a real Altadena builder through the lookup. Full disclosure: JMB Builders LLC (CSLB #1103479) is a paid featured builder on Altadena ADU Builder, but the verification process below works identically for any contractor you're considering.

Start at the CSLB's official Check a License tool and enter the license number — the fastest search type, since it takes you straight past the summary to the detail page, which is what actually matters. If a number doesn't come up at all, that's a stop sign: the license is expired, cancelled, inactive, or was never issued.

Here's what to confirm on the detail page for any ADU builder:

• Status is "Active" — inactive isn't necessarily bad, but the contractor can't legally take new work in that state.
• Classification includes Class B — General Building, the classification that covers ADUs, additions, and full remodels.
• The $25,000 surety bond is on file — remember, it's a recovery mechanism for harmed homeowners, not insurance.
• Workers' compensation is current, or a valid exemption exists for a genuine sole operator.
• The legal business name on CSLB matches the proposal and contract exactly — a name mismatch is one of the most common scam patterns.

JMB Builders LLC checks these boxes: an Altadena-based Class B general contractor building custom homes, ADUs, and whole-home remodels, including Eaton Fire rebuilds, with its work documented on jmb-builders.com. Run the number yourself — that's the whole point of this exercise. A clean result takes about five minutes and costs nothing.

One caveat: a clean CSLB record isn't proof of perfection, because most consumer complaints are resolved or dropped and never appear. Supplement the lookup with recent references and a written estimate. And re-check the license before each payment — a contractor who was active last month could be suspended today.

If you find a problem — a suspension, missing bond, or classification that doesn't match the work — don't sign. Stop all work if a suspension surfaces mid-project, and call the CSLB complaint line at 800-321-CSLB (2752). If everything checks out, you're ready for the real conversation: whether your lot, budget, and goals support an ADU. Altadena ADU Builder offers a free ADU feasibility consultation with a cost-quiz concept render — a practical next step once the license check is behind you.