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An address validator should explain what it found and what the person should do next—not just return “valid” or “invalid.” A boolean hides whether a unit number is missing, a street detail is uncertain, or the system silently changed the address. It can also make a result sound like a delivery guarantee when it is only a validation signal.
For developers, the practical answer to “What should an address validation API return?” is a structured outcome with reasons, evidence, and a clear next action. For product teams, that structure makes address validation errors more useful and less likely to send someone to the wrong destination.
Why a boolean is not enough
A boolean compresses several different situations into the same two outcomes. “Invalid” might mean a required apartment number is missing, a supplied unit could not be confirmed, or the street address itself failed to match. “Valid” might mean an address was normalized or partially confirmed—not that a carrier is certain to deliver there.
Google’s Address Validation API provides a more useful model: a verdict gives a baseline summary, while address details, geocode, metadata and, for US and Puerto Rico addresses, USPS data provide supporting signals. Google describes the verdict as a baseline summary of address quality in its response documentation. Treat that summary as an entry point, not a complete explanation.
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Return the reason and the next action
A useful response separates the compact outcome from the evidence behind it and the instruction shown to the user. For example, an application might return:
status: a compact outcome such asneeds_input,confirm_suggestionoraccepted.reasons: stable codes such asmissing_subpremise,unconfirmed_componentoraddress_corrected.message: localized, plain-language wording that identifies the specific issue.suggested_address: the normalized or corrected address, when available.signals: supporting details such as completeness, validation granularity and geography-specific postal checks.next_action: a direct instruction, such as add a unit, review a correction or continue.
These field names are an application design pattern, not a provider-defined schema. Keep the provider’s raw signals alongside your own reason codes so policy and wording can change without discarding the underlying evidence.
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Use the result to guide the user
Google’s workflow guidance illustrates distinct paths: fix likely significant issues, request a missing subpremise, ask the user to confirm corrections, or accept a sufficiently strong result. The useful design principle is to translate signals into a specific prompt instead of exposing a generic failure.
- Missing unit: “Add an apartment, suite or unit number if this destination has one.”
- Unconfirmed component: “We could not confirm this part of the address. Check the street number and street name.”
- Suggested correction: “We found a possible correction. Confirm that this is the address you intended.”
- Strong enough for your workflow: “Address accepted,” if your application is comfortable proceeding with the available evidence.
Acceptance is a product decision based on the consequences of an error. It does not turn a validation response into a promise of postal delivery.
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Distinguish a missing unit from a wrong address
For US addresses, Google’s USPS Delivery Point Validation (DPV) data can distinguish cases that a single failure flag would obscure. Google’s reference documentation describes the DPV confirmation values:
| DPV value | What it indicates | Useful response |
|---|---|---|
Y |
The primary address and any secondary numbers were confirmed. | Proceed if the rest of your application’s acceptance policy allows it. |
D |
The primary number matched, but secondary information was missing. | Ask for a unit number when the destination may require one. |
S |
The primary number matched, but the supplied secondary information was not confirmed. | Ask the user to check the apartment, suite or other unit detail. |
N |
The primary address and any supplied secondary information failed to confirm. | Ask the user to review the street address and any unit details. |
| No DPV value | No confirmation value was returned; this is not the same as a confirmed result. | Use the other available response fields rather than treating absence as confirmation. |
These are US USPS-specific signals, not universal postal codes. Google notes that USPS data may be absent, so an application should interpret DPV together with the rest of the response rather than make it the sole decision point.
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Make corrections and uncertainty visible
A validator may infer, replace or spell-correct a component and return a normalized suggestion. That can help make an address usable, but a changed component may also point somewhere other than the user’s intended destination. When a meaningful correction is proposed, show the suggested address and ask the user to confirm it instead of silently replacing what they entered.
Validation granularity also matters: a result established only below the premise level may not confirm the exact destination. Explain what the service did establish, and avoid language that implies it verified a specific apartment or door when it did not. Google’s response documentation describes verdict and address-component signals; its response guidance cautions against treating each component’s confirmation level as a fixed integration contract. Build from documented response signals and retain flexibility as the integration evolves.
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Set acceptance rules around your risk
Not every workflow needs the same threshold. A low-consequence form may allow a user to continue after seeing a correction prompt. A shipment or service visit may need the recipient to resolve an uncertain unit or street number first. The relevant question is not simply whether the API said “valid”; it is whether the available evidence is adequate for this action.
Keep the policy separate from the provider response: preserve raw validation signals, map them to stable application reasons, and decide which outcomes need input, confirmation or can proceed. The API supplies evidence; your application decides what risk it will accept.
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