What does it mean when GPSLarp says it could not tell?

That the check ran and its answer could not be interpreted. It is deliberately not a pass and deliberately not a failure. Nothing about the phone has been diagnosed and nothing has been changed, and the cause is usually on the Mac rather than on the phone.

Why does GPSLarp not just say Developer Mode is off?

Because iOS refuses to answer that question at all unless the phone is unlocked and trusts the Mac, and the refusal arrives as a different thing from a genuine answer of off. Treating the refusal as an answer would tell somebody whose phone is merely locked that Developer Mode is off, and send them into Settings and a restart of the phone for a problem they do not have.

Why do the checks below the message say Not checked?

The checks run in dependency order and the application stops at the first one it cannot get past. Everything after that point is reported as not checked rather than as failing, because a check that never ran is not a check that failed. One message with several not-checked rows under it is one problem.

Should I reinstall GPSLarp when it cannot check my iPhone?

Only for one of the seven messages: the one saying the component it uses to talk to iPhones did not load, which points at the copy you installed rather than at the phone. The other six are about the Mac, the cable, the network or another program holding the connection, and a reinstall does nothing for any of them.

Does an unreadable check mean something is wrong with my iPhone?

No. It means the question was not answered, which is a statement about the attempt rather than about the phone. The application says outright that the step has not been ruled out and has not been confirmed, and that sentence should be read literally rather than as a polite refusal.

GPSLarpHelp

GPSLarp says it couldn't check my iPhone

The app does not name a problem with your phone. It says it could not tell, or that something was not checked, or that a step has not been ruled out and has not been confirmed.

This is a real outcome rather than a vague one, and reading it as a failure sends you the wrong way. GPSLarp separates we asked and the answer is no from we could not ask, and it will not turn the second into the first. Nothing on your phone has been diagnosed, nothing has been changed, and the fix is almost always on the Mac.

01What "could not tell" is doing here

Before GPSLarp will set a location it checks seven things in order: that a phone is attached, that its iOS is new enough, that it trusts this Mac, that it is unlocked, that Developer Mode is on, that the support file iOS wants is installed, and that the connection on the Mac is running. Each of those checks ends in one of four states, and only one of them is a verdict about your phone:

Fine. The check ran and this step is satisfied.
This is what is stopping you. The check ran, the answer came back, and the answer is the problem. This is the only state that asserts anything about your phone, and it is reachable only from a successful read.
Could not tell. The check ran and the answer could not be interpreted. Not a pass, not a failure, and never dressed up as either.
Could not be attempted. The check never got as far as asking. The problem is this Mac or this copy of GPSLarp, not the phone.

Most of this help centre is about the second state. This page is about the last two.

Why the app goes to this trouble

The clearest case is a locked iPhone. iOS refuses to answer the question GPSLarp uses to read the Developer Mode setting unless the phone is unlocked and trusted — and the refusal and a genuine "Developer Mode is off" arrive as two different things. Treating the refusal as an answer would tell somebody whose phone is simply locked that Developer Mode is off, and send them into Settings and a restart of the phone to fix a problem they do not have. So a phone that is merely locked is told it is locked, and a question that could not be asked is reported as a question that could not be asked.

02Which message do you have

Seven sentences carry this outcome and each names a different point in the chain. Find yours; the next section is arranged in the same order.

01The check itself did not finish

GPSLarp could not finish checking your iPhone. Nothing about the phone has been ruled out — this is the check itself failing, not a problem it found.

The whole check ran out of time or fell over. Nothing below was reached.

02GPSLarp cannot talk to iPhones at all

GPSLarp could not load the component it uses to talk to iPhones, so it could not check anything about your phone. This is a problem with this copy of GPSLarp rather than with your iPhone. Reinstalling it is the fix.

The part of the app that speaks to phones did not load. This is the only message on the page that points at the download you installed.

03macOS would not say what is attached

GPSLarp could not ask macOS which devices are attached, so it could not tell whether your iPhone is connected. This is a problem on this Mac rather than on your phone.

The service macOS uses to keep track of attached iPhones did not answer. Note the difference from an empty list: an empty list is an answer, and it has its own page.

04The phone is there and would not open

GPSLarp found your iPhone but could not open a connection to it, so nothing below this point could be checked.

macOS listed the phone and the connection to it failed. Very often this is another program holding it — see below.

05The iOS version would not read

GPSLarp could not read which version of iOS your iPhone is running, so it cannot say whether this iPhone is supported.

There is a version requirement and this is the app declining to guess whether your phone meets it.

06Trust could not be established either way

GPSLarp could not tell whether your iPhone trusts this Mac. It has not been ruled out and it has not been confirmed.

Read that second sentence literally. It is not a polite way of saying the phone does not trust the Mac.

07The support file could not be established either way

GPSLarp could not tell whether your iPhone has the developer disk image it needs. It has not been ruled out and it has not been confirmed.

Same shape, one step further down. What that file is has its own page.

Underneath whichever of those you have, the remaining rows will say Not checked — an earlier step has to be sorted out first. That is not a list of further problems. The app stops at the first thing it cannot get past, so one message with several "not checked" rows under it is one problem.

03What to do, in this order

These are ordered by how often each one turns out to be the answer, not by the order the messages appear in.

01Unlock the iPhone and leave it awake

Then ask GPSLarp to check again. A locked phone refuses most questions, and although the app has a specific message for a phone it can positively identify as locked, a phone that locks itself midway through can land in the unreadable messages instead. This costs nothing and rules out the most common cause.

02Close anything else on the Mac that talks to the phone

Finder with the iPhone selected, Xcode, Apple Configurator, and above all a second copy of GPSLarp. Only one program at a time may hold the connection to an attached iPhone, and the loser gets a message about not being able to look. This has its own page because it comes up constantly: Another program on my Mac is using my iPhone.

03Reseat the cable, or plug in if you were on Wi-Fi

A cable that carries power but not data, a hub, and a phone that has drifted off the shared network all produce reads that start and do not finish. A direct cable into the Mac takes the network out of the question entirely. Which to use and why is Cable or Wi-Fi — which should I use?

04Ask GPSLarp to check again

Every check above the connection step runs without your administrator password and finishes in a fraction of a second, so re-checking is cheap and you can do it after each change. The app does not watch the phone in the background — nothing re-checks itself.

05Restart the Mac, then the phone

In that order, and only after the four above. Restarting the Mac releases every held connection and restarts the service that tracks attached devices, which is what most of these messages are about. Restarting the iPhone clears the support file iOS had mounted, so expect the app to want to install that again — that is normal and is explained on My iPhone is missing a file iOS needs first.

06Reinstall GPSLarp, but only for one message

The message about the component the app uses to talk to iPhones is the only one pointing at the app itself. For that one, install the package over the top of what you have — nothing needs removing first and your saved places are untouched. See The installer won't open, or I can't find the app.

04If that did not work

Your Mac is managed by an employer or a school. A management profile can restrict which programs may speak to attached devices, and the result looks exactly like this: reads that begin and do not complete, with no error naming the policy. Nothing in GPSLarp works around that and no setting changes it.

The message changes each time you check. That usually means the connection is intermittent rather than absent — a marginal cable, a hub, or Wi-Fi. Go to a direct cable and check three times in a row before concluding anything.

It says a step is blocked rather than unreadable. Then you have an answer and this is no longer your page. Each blocked step has its own: no phone found, trust, Developer Mode, the support file, and the connection on the Mac.

Two iPhones are attached. Worth knowing that the checks only ever describe one of them — Can I use GPSLarp with more than one iPhone?

The honest limit of this page: it explains an outcome the app reports and what tends to produce it. Clearing one of these lets the checks carry on; that is not the same as a location change, and nobody in this project has watched one happen on a real iPhone from beginning to end. Every account gets a free run of each mode because running it on your own phone is the only way to find out.