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A postal code API returns structured location data for a given ZIP Code or Canadian postal code. A typical response includes the code itself, city, state or province, county, latitude/longitude, and — where available — ZIP+4 detail. More complete services add time zone, area codes, boundary geometry, and demographic fields. You send a code (or an address), and the API sends back a machine-readable record you can store, validate, or display.

This article explains what those responses contain, how requests are usually shaped, and where postal code data fits into real applications.

First, clear up the word "code"

The keyword "code" is overloaded, and that causes real confusion for developers:

• Postal code — the ZIP Code (U.S.) or postal code (Canada) that identifies a delivery area.
• API key — the credential you use to authenticate your requests. It is not postal data.
• Source code — the program you write to call the API.

When someone searches for "postal code API code," they usually want example request/response code for a postal code service. The rest of this article treats it that way.

What a postal code API actually returns

Response fields vary by provider and endpoint, but the core set is fairly consistent. A single-code lookup commonly returns:

Richer datasets add 90+ fields: boundaries, population, income, elevation, and more. You rarely need all of them — request only what your application uses.

A representative JSON response

{
  "postal_code": "90210",
  "city": "Beverly Hills",
  "state": "CA",
  "county": "Los Angeles",
  "latitude": 34.0901,
  "longitude": -118.4065,
  "timezone": "America/Los_Angeles",
  "area_codes": ["310", "424"]
}

XML responses carry the same information in tag form. Choose based on what your stack parses most easily; JSON is the common default.

Common request patterns

Most postal code APIs support four patterns. Knowing which one you need prevents wasted calls.

1. Lookup by code

You have a code and want its details. This is the simplest and fastest call.

GET /lookup?code=90210

2. Reverse lookup by address

You have a street address and want to confirm or complete the code. This is the pattern behind checkout address validation.

GET /validate?street=...&city=...&state=...

3. Radius search

You have a center point and want all codes within a distance. Useful for store locators and delivery zones.

GET /radius?code=90210&miles=10

4. Batch validation

You have a file of addresses and want them cleaned in bulk. Batch endpoints trade latency for throughput and usually have their own limits.

Handling missing and ambiguous matches

Real data is messy. Plan for these cases:

• No match — the code doesn't exist or the address is malformed. Return a clear error rather than a silent empty object.
• Multiple matches — a city name may map to several codes, or a code may span several acceptable city names. Decide whether to pick the primary or return a list.
• Partial match — the street is valid but the ZIP+4 isn't. Fall back to the 5-digit code.
• Stale data — codes are added, retired, and reassigned. Refresh your dataset on a regular schedule.

A practical rule: validate at the point of entry, store the normalized result, and never re-derive it later from raw user input.

Practical use cases

• Checkout address validation — catch typos before shipping, reduce failed deliveries.
• Shipping zone lookup — map a code to a zone, carrier route, or rate table.
• Data enrichment — append county, coordinates, or demographics to existing records.
• Store and service locators — radius search to find nearby branches or coverage areas.
• Territory and tax logic — county and boundary data drive jurisdiction rules.

Licensing and data-source considerations

Postal code data originates with national authorities — USPS in the United States and Canada Post in Canada. Providers license and repackage it, which is why accuracy, update frequency, and field coverage differ between services. Before committing:

• Confirm the data source and how often it refreshes.
• Check whether ZIP+4 and boundary data are included or sold separately.
• Review usage limits and whether batch processing is allowed.
• Read the license terms for redistribution and storage.

Pricing and plan details change, so check the provider's current documentation rather than relying on secondhand figures.

Getting started

1. Decide which request pattern you need (lookup, reverse, radius, or batch).
2. Pick the fields you'll actually store.
3. Write a small test call and inspect the raw response.
4. Add error handling for no-match and ambiguous cases.
5. Cache results where the same codes repeat.

A postal code API is ultimately a translation layer: you give it a code or an address, and it gives back structured location facts. Understand the fields, match them to your use case, and handle the messy edges — that's most of the work.

i3 was written from scratch after its authors tried to hack and fix wmii, and the differences follow directly from that experience. Compared with wmii, i3 uses libxcb instead of Xlib, replaces wmii's 9P filesystem interface with a lighter IPC interface, arranges windows in a tree rather than columns, and assigns each workspace to a virtual screen so multi-monitor setups (including hot-plugged projectors and rotated monitors) behave correctly. It keeps the minimal-window-manager ethos — simple borders, no bloat — but deliberately does not cap its own size in lines of code when a feature needs the room.

The starting point: lessons from wmii

The i3 project began with a concrete frustration: wanting to hack or fix wmii. Rather than patch around that codebase, the authors agreed on a set of goals and wrote a new tiling window manager. Those goals are the clearest statement of how i3 positions itself against wmii and similar minimal window managers.

Design differences at a glance

The xcb choice is justified on two grounds: a cleaner API and expected speed gains in many situations. The IPC choice is justified as more lightweight than wmii's 9P approach, and because core functionality does not depend on a separate program — which matters most when the system is under load.

What the tree structure changes

Most tiling window managers arrange windows in columns. i3 instead uses a tree structure to arrange windows, which the project describes as enabling more flexible layouts than the column-based approach used by other window managers. If your workflow involves nesting splits — a horizontal pair inside a vertical stack, for instance — that is the structural difference you will feel day to day.

Multi-monitor behavior

i3's stated goal is to implement multi-monitor support correctly by assigning each workspace to a virtual screen. The specific cases called out are attaching and detaching new monitors, such as video projectors, during operation, plus support for rotated monitors. If you move between a laptop panel and an external display regularly, this is the design area to evaluate first.

Modes and IPC

Two features have no counterpart in the wmii description:

• Modes, modeled on vim. You can bind different keys in a resize mode than in the default mode, so destructive or rarely used commands do not need to occupy your main keymap.
• IPC, aimed at other programs. It supports subscribing to certain events and accepting commands.

Who i3 is aimed at

i3 states it is primarily targeted at advanced users and developers. The project also commits to well-readable, well-documented code and to documentation explaining internal workings, so that people who can program but are not familiar with all of X11 internals can still follow why and when things happen. That documentation goal is itself a differentiator from window managers you are expected to read purely as source.

Trade-offs to weigh

• Minimalism with an escape hatch. i3 keeps the usual minimal-window-manager stance — no bloat, no fancy decoration beyond simple borders — but explicitly refuses to enforce limits such as a maximum number of source lines. If a feature needs more code, it gets more code.
• Stability over new features. The project says it is generally happy with the feature set and now focuses on fixing bugs and maintaining stability; new features are considered only when the benefit justifies them. If you need a rapidly expanding feature list, that is a mismatch.
• Licensing and platforms. i3 is Free and Open Source Software under the BSD license, targeting GNU/Linux and BSD operating systems.

Practical next step

To judge the differences yourself rather than from a feature table, the project points to three entry points on i3wm.org: watch the screencast, read the User's Guide, and install i3. The current version listed there is 4.25.1. Running it against your own monitor arrangement and keybinding habits will tell you more about the tree layout and mode system than any comparison can.

i3wm.org is the official home of i3, a tiling window manager for GNU/Linux and BSD. From that site you can download the latest version (the page currently lists 4.25.1), read the User's Guide, and watch a screencast. The project is Free and Open Source Software under the BSD license, and it is primarily aimed at advanced users and developers.

What you can get from i3wm.org

The site presents three main entry points, each matching a different stage of getting started:

The page's own framing is "Do What I Mean. Good Docs. Clean Code. Sounds good?" — which reflects the project's stated priorities rather than a marketing claim.

Before you install: what i3 actually is

i3 is a tiling window manager written completely from scratch. Its target platforms are GNU/Linux and BSD operating systems. If you are coming from a stacking window manager, the behavior will be different: windows are arranged by a tree structure rather than overlapping freely.

Two design points are worth knowing before you commit:

• Tree structure for layouts. i3 arranges windows in a tree, which allows more flexible layouts than the column-based approach used by other window managers.
• Modes, like in vim. You can use different keybindings in a 'resize' mode than in the default mode, for example.

Documentation and code as first-class resources

The project states that it wants well readable, well documented code, and that it documents how to extend i3 by explaining its internal workings. That documentation is intended to be usable by people who know how to program but are not necessarily familiar with all of X11's internals — it explains why things happen and when they happen, so a reader can build a picture of the whole process a window manager is responsible for.

If your goal is only to use i3, the User's Guide is the relevant document. If your goal is to modify i3, the source-level documentation is the one the project points to.

Multi-monitor and rotated screens

If you use more than one display, this is a documented area of focus rather than an afterthought. i3 implements multi-monitor support by assigning each workspace to a virtual screen. The project specifically calls out making sure that attaching and detaching new monitors — such as video projectors — works during operation and does the right thing. Support for rotated monitors is also provided.

How i3 relates to wmii

i3 was informed by the experience of wanting to hack on and fix wmii. The stated goals that came out of that experience include using xcb instead of Xlib (a cleaner API, and faster in many situations) and implementing an IPC interface for other programs, with subscription to certain events and acceptance of commands. The project describes this IPC approach as more lightweight than wmii's use of the 9P filesystem, and notes that core functionality does not depend on a separate program, so i3 runs faster, especially when the system is under load.

A note on project direction

The page states that the maintainers are generally happy with the feature set of i3 and instead focus on fixing bugs and maintaining it for stability. New features will therefore only be considered if the benefit — the sentence is cut off at that point on the page — so if you are choosing i3 expecting rapid feature expansion, that is not the stated direction.

Practical next step

Go to i3wm.org, download the latest version listed there, and read the User's Guide before your first session. If you want to see the interaction model first, watch the screencast. The download page is the authoritative source for the current version number, so check it rather than relying on a version quoted elsewhere.

i3wm.org is the official website for i3, a tiling window manager written from scratch for GNU/Linux and BSD operating systems. It is free and open source software under the BSD license, aimed primarily at advanced users and developers. The site serves as the project's home for downloads, documentation, and demonstration material.

What i3 is

i3 is a tiling window manager — rather than letting windows float and overlap, it arranges them automatically so they fill the screen without gaps or wasted space. The project describes itself as completely written from scratch, with the target platforms being GNU/Linux and BSD.

The stated design goals, as listed on the site, include:

• Readable, well-documented code — documentation covers how to extend i3 and explains its internal workings, so users can understand the whole process a window manager is responsible for just by reading the source.
• xcb instead of Xlib — chosen for a cleaner API and better performance in many situations.
• Correct multi-monitor support — each workspace is assigned to a virtual screen, with support for attaching and detaching monitors (such as projectors) during operation, plus rotated monitors.
• A tree structure for arranging windows — enabling more flexible layouts than the column-based approach used by other window managers.
• Modes, like in vim — for example, different keybindings in a "resize" mode than in the default mode.
• An IPC interface — other programs can subscribe to events and send commands, described as more lightweight than wmii's use of the 9P filesystem, with core functionality not depending on a separate program.
• UTF-8 clean handling.

On the visual side, the project takes a deliberately minimal stance: simple borders are described as the most decoration wanted, and the team states it is generally happy with the current feature set, focusing on bug fixes and stability rather than new features.

Who it is for

The site states i3 is primarily targeted at advanced users and developers. If you want a window manager that stays out of the way, is keyboard-driven, and whose behavior you can understand and modify from the source, i3 fits that profile. If you prefer a conventional desktop with floating windows and heavy visual decoration, i3's minimal, tiling approach is a different model.

What you can find on i3wm.org

The homepage points to three main entry points:

• A screencast — to see i3 in action before installing.
• The User's Guide — the documentation for learning how to use it.
• Download — the latest version listed on the page is 4.25.1.

Getting started

1. Watch the screencast to confirm the tiling workflow suits you.
2. Read the User's Guide to learn the default keybindings and configuration.
3. Download the latest version (4.25.1 as listed) and install it on GNU/Linux or BSD.

Because i3 is FOSS under the BSD license, you can read, modify, and redistribute the code. The project's emphasis on documented internals means that even users who are not familiar with all of X11's internals are intended to be able to follow how and why things happen.

i3 treats each monitor as a separate X virtual screen and assigns workspaces to those screens, so multi-monitor support is built into its core design rather than bolted on. According to the project's own description, i3 implements multi-monitor support "correctly, that is by assigning each workspace to a virtual screen," and it explicitly aims to make attaching and detaching monitors — such as video projectors — work during operation. Rotated monitors are also listed as supported. This applies to i3 on GNU/Linux and BSD, where the window manager runs on top of X11.

The core mechanism: one workspace, one screen

i3's model is straightforward:

• Each physical monitor is exposed to i3 as a virtual screen.
• Each workspace belongs to exactly one screen at a time.
• When you switch to a workspace, i3 displays it on the screen that workspace is assigned to.

This is why i3's multi-monitor behavior feels predictable: you are not stretching one desktop across several displays, you are moving whole workspaces between them. The project describes this as the "correct" approach and contrasts it with window managers that handle multiple monitors less cleanly.

Dynamic attach and detach

The project states that i3 is designed so that "attaching and detaching new monitors like video projectors works during operation and does the right thing." In practice this means you can plug in a projector or an external display while your session is running, and i3 will account for the new screen without requiring a restart of the window manager.

The same applies in reverse: unplugging a monitor is handled at runtime. Because workspaces are tied to screens, the important question after a detach is where the workspaces that lived on the removed screen end up — i3's screen-to-workspace assignment is what governs this.

Rotated monitors

Rotated monitors are listed among i3's supported features. Rotation itself is typically configured at the X level (for example through your display configuration), and i3 then treats the rotated output as a screen with the corresponding dimensions. The project's stated goal is that rotated monitors are supported alongside the normal multi-monitor case.

Extended Xinerama support

i3's description highlights "extended Xinerama support." Xinerama is the X11 mechanism for presenting multiple physical displays as separate screens to applications. i3 builds its multi-monitor behavior on this model, which is why each monitor maps to a virtual screen and why workspace-to-screen assignment is the central concept.

What this means for you

If your workflow depends on moving whole workspaces between displays, keeping a fixed layout per monitor, or connecting and disconnecting external screens without restarting your session, i3's design targets exactly those cases. The project positions itself as aimed primarily at advanced users and developers, so expect to configure display and workspace behavior yourself rather than relying on a graphical setup wizard.

For the authoritative details on configuring outputs and assigning workspaces to specific screens, the i3 User's Guide linked from i3wm.org is the reference to follow; the current release listed on the site is 4.25.1.