Recommended Free Tools
iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
A current business-registration lookup can tell you a company’s status now. It may not give you a usable record of what the service returned yesterday. Yoon’s answer was to query a fixed list of companies every day, keep each result, and compare it with the previous snapshot. The history is not an upstream event log: it is a record of what the system observed, and when.
Why keep a history when the API already returns a status?
A one-time lookup answers a present-tense question: what does the service report about this registration at the time of the query? A recurring watchlist answers a different question: how did the reported status change between observations?
Yoon describes Korea’s National Tax Service business-registration status service as returning current information without a history endpoint, changelog, or as_of parameter. The Korean Public Data Portal’s listing confirms that the API provides operating status, tax type, and closure-date information, but the listing reviewed does not establish whether another historical facility exists. So the lack of upstream history is Yoon’s account, not a conclusion proved by the portal listing. Korean Public Data Portal API listing.
Free tools Windows power users keep installed
One-click scans. No signup required.
The practical idea is straightforward: if a source gives you only its latest state, retaining your own observations can create a timeline the source itself may not provide. That timeline is valuable only if its limits are clear.
#1 Best Overall
- Easily store and access 2TB to content on the go with the Seagate Portable Drive, a USB external hard drive
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
How the daily snapshot and comparison work
Take a complete observation
Yoon’s scheduled job queries a fixed list, then saves a daily snapshot of the returned statuses. The fixed list matters: it defines what the job is watching, rather than turning the process into an ad hoc record of every lookup someone happens to make.
Compare against the prior observation
After storing the current results, the job compares them with the previous day’s results and writes a separate changes file. The snapshot preserves the complete observation; the diff makes changes easier to inspect. A diff is meaningful only relative to its baseline, so it should not replace the snapshots it was derived from.
Rank #2
- Easily store and access 5TB of content on the go with the Seagate portable drive, a USB external hard Drive
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Keep observation time separate from event time
If one snapshot reports a business as active and the next reports it closed, the system can establish that the observed state changed between those checks. It cannot establish the exact moment the closure occurred. Yoon’s account says the stored timestamps mark the observations, not an inferred event time. In his words: “I can’t prove when it actually closed — only when I observed each state.”
What the first three runs showed—and did not show
Yoon reports 211,243 observations per day in each of the first three runs. In that initial sample, he counted 70 status changes on day two and 94 on day three. Those figures describe his system over three days; they are not a general rate of business-status change or an independent benchmark.
Rank #3
- Easily store and access 1TB to content on the go with the Seagate Portable Drive, a USB external hard drive.Specific uses: Personal
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop. Reformatting may be required for Mac
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
He reports that each daily snapshot was approximately 42 MB and the changes file approximately 1.7 MB. These are the file sizes in his implementation, not a guarantee for other formats, fields, compression settings, or watchlist sizes.
The first run could not test whether the comparison logic correctly identified changes: with no prior snapshot, every row was new. Yoon says meaningful validation began on day two, when the new results could be compared with a stored baseline. For a similar job, treat the initial run as baseline creation, then inspect later diffs against known or manually checked records before trusting them.
Rank #4
- Easily store and access 4TB of content on the go with the Seagate Portable Drive, a USB external hard drive.Specific uses: Personal
- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
One lookup versus a recurring watchlist
| Approach | Best fit | How it runs | What it returns or preserves | What the evidence can establish |
|---|---|---|---|---|
| One-time lookup | You need the service’s current response for a particular registration. | Work starts when someone or something makes a query. | The queried record’s current status information. | What the service reported at lookup time; not a timeline unless you separately retain results. |
| Recurring watchlist | You need to track a defined set of records over time. | A scheduled job queries the list and compares each run with a retained prior snapshot. | A complete daily snapshot plus a separate file of differences in Yoon’s workflow. | Which observed results differed between recorded checks; not necessarily when an underlying change happened. |
API limits and timing shape the job
The Public Data Portal listing describes the National Tax Service interface as a free REST service, updated from NTS data on a 30-minute cycle. It cautions that newly opened businesses may take one to two days to appear. The listing specifies up to 100 records per request and a daily limit of one million calls; it was modified May 13, 2026. These are portal-listed service details, not a promise that a new registration will be visible immediately. Check the official API listing for its current details.
Yoon estimates roughly 2,100 upstream calls per day for his workload. That is a request count, distinct from the 211,243 individual observations: the portal allows up to 100 records in a request. His estimate is specific to his workload and does not mean every watchlist of that size will make exactly that number of calls; request batching and API behavior determine the actual count.
Best Value
- [Upgraded Version] - This external hard drive features a mirrored logo stripe combined with a striped anti-slip design, and the rounded corners of the casing make it easier to grip. The stripes also have a heat dissipation function, ensuring stable and fast data transfer.
- 【Ultra-thin and quiet】 - The motherboard adopts JMicron 578 noise-free solution, giving you a quiet working environment. Lightweight and portable size designed to fit in your pocket for easy portability.
- 【Ultra-Fast Data Transfers】 - Pairing this external hard drive with JMicron 578 solution USB 3.0 and USB 2.0 interfaces enables blazing-fast data transfer. It boasts theoretical read speeds of up to 125MB/s and write speeds of up to 103MB/s.
- 【Plug and Play】 - With no software to install, just plug it in and the drive is ready to use.The hard disk chip is wrapped with an aluminum anti-interference layer to increase heat dissipation and protect data.
- 【What You Get】 - 1 x Portable Hard Drive, 1 x USB 3.0 Cable, 1 x User Manual, Gift-type shell packaging ,Three-year manufacturer's warranty and free technical support services.
Make sure the scheduled job actually does useful work
A scheduler can report success even if the program exits without performing its task. Yoon reports that a Linux entry-point guard failed in a way that returned successfully but did no work; running the program manually exposed the problem. A reliable monitoring setup should therefore verify outcomes, not just process exit status.
- Check that a run produced a snapshot with the expected record count, not merely a zero exit code.
- Check that the snapshot timestamp advances on schedule and that the diff corresponds to the intended prior snapshot.
- Alert on missing or unexpectedly small output, failed requests, and malformed responses.
- Run the entry point manually in the same environment the scheduler uses, then confirm its output and logs.
- Validate diff behavior after a baseline exists; a first run has no prior state against which to detect changes.
Choose and guard the data source deliberately
A retained history can carry sensitive implications even when the source is public. Yoon says his tracked company list came from public procurement and debarment registries, rather than customer lookup queries, and describes runtime and test guards intended to keep the watchlist within that scope. The broader lesson is to define why each record is included, preserve that provenance, and test that the job does not quietly expand beyond its intended list.
Snapshots also need enough context to be interpretable later: the query date and time, the source, the identifier used, and the response fields observed. Keeping those with the result makes it less likely that a later reader mistakes an observation for an authoritative historical event record.
What this pattern is—and is not
It is a way to build an observed history from repeated present-state queries. It is not proof that the underlying source has no historical capability anywhere, nor does it reconstruct exact event times that were never returned. The phrase “data nobody sells” is Yoon’s framing of a gap he wanted to fill, not a verified survey of every data provider or market.
For anyone wrapping a public data source for agents or other software, the useful design question is not only what the endpoint returns. It is also what it leaves unanswered—and whether retaining observations is an appropriate, auditable way to answer those questions later.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
