Learn Hardcore German: Jede kleine Verbesserung im Text macht uns sicherer für die Abgabe. - Every small improvement in the text makes us more confident for the submission.

In the sentence, Verbesserung is the subject, so it is in the nominative singular.
The correct form of jede in nominative singular feminine is jede.
The adjective before a feminine noun with a determiner like jede gets the ending -e → kleine.

So:

jede kleine Verbesserung = correct (feminine nominative singular)
jeder kleine Verbesserung = wrong (that would be masculine nominative)
jedes kleine Verbesserung = wrong (that would be neuter nominative)

Why is Verbesserung singular (jede kleine Verbesserung) and not plural, like alle kleinen Verbesserungen?

Both versions are possible, but they emphasize slightly different things:

jede kleine Verbesserung = every single small improvement (focus on each one individually)
alle kleinen Verbesserungen = all the small improvements (focus on the whole set)

The sentence with jede highlights that each individual improvement, no matter how small, contributes to us feeling more confident. It’s a typical style in German: jede + singular to express “every”.

Why is it kleine and not kleiner in jede kleine Verbesserung?

Adjective endings depend on:

The case: here, nominative
The gender: feminine (die Verbesserung)
The determiner: we have jede, which already shows the gender and case

With a determiner like jede, the adjective takes a weak ending:

nominative feminine: jede kleine Verbesserung

kleiner would be used, for example, in dative plural or genitive feminine in some patterns, but not here.

What case is Verbesserung in, and what role does it play in the sentence?

Verbesserung is in the nominative case because it is the subject of the verb macht.

Jede kleine Verbesserung im Text = subject
macht = verb
uns = object
sicherer für die Abgabe = what it makes us (predicative complement + prepositional phrase)

So the structure is basically:
Subject makes Object more sure (for the submission).

What exactly is im in im Text? Why not just in Text?

im is a contraction of in dem:

in
- dem (dative masculine for der Text) → im

You cannot say in Text here. You need an article:

im Text = in dem Text = in the text

German frequently contracts preposition + article:

in dem → im
an dem → am
zu dem → zum, etc.

Why is it im Text (dative) and not in den Text (accusative)?

The preposition in can take dative or accusative, depending on the meaning:

Dative = location (where?)
Accusative = direction/movement (where to?)

Here, im Text answers “Where is the improvement located?” → It is in the text, a location, not a movement. So dative is used:

im Text = in the text (location)
in den Text = into the text (movement, e.g. Wir fügen etwas in den Text ein – We insert something into the text.)

That’s why im Text (dative) is correct here.

What case is uns in macht uns sicherer, and why?

uns here is accusative plural, functioning as the direct object of macht.

Pattern: etwas macht jemanden (etwas):

etwas (subject)
macht (verb)
jemanden (accusative object)
[adjective / comparative] (what they are made)

So:

Jede kleine Verbesserung = subject
macht = verb
uns = accusative object (whom does it make more confident?)
sicherer = predicative adjective, describing uns

uns in nominative would be wir; that would be wrong here.

Why is it sicherer and not just sicher?

sicher can mean safe, sure, or confident.

sicher = sure/confident
sicherer = more sure / more confident

Using the comparative (-er) shows that our level of confidence increases with each improvement.

Both are grammatically possible:

macht uns sicher = makes us confident
macht uns sicherer = makes us more confident

In this context, sicherer fits better because the idea is gradual improvement in confidence.

How is the comparative sicherer formed, and why is there no umlaut or anything else?

The base adjective is sicher. The regular comparative in German is usually formed by:

adding -er to the adjective: sicher → sicherer

No umlaut is added here because sicher has no suitable vowel for an umlaut change, and it’s a regular adjective. Examples:

kalt → kälter (with umlaut)
sicher → sicherer (just -er)

So sicherer is simply the regular comparative form.

Why is it für die Abgabe and not something like bei der Abgabe or zur Abgabe?

für always takes the accusative and usually expresses purpose, benefit, or aim:

für die Abgabe = for the submission / with regard to the submission

Alternatives have slightly different nuances:

bei der Abgabe = at the (time of) submission (a circumstance in time/place)
zur Abgabe = for submission / to submit (often more about the act of submitting itself or the purpose of preparing something)

Here, we want to say that these improvements make us more confident with respect to the submission, so für die Abgabe is the most natural.

What does Abgabe mean exactly, and what gender is it?

Abgabe is a feminine noun: die Abgabe.

Common meanings include:

the act of handing in / submitting something (e.g. homework, a thesis)
sometimes: a fee / tax / charge (in other contexts)

In this sentence, die Abgabe clearly means the submission (e.g. of a text, a paper, an assignment).

So:

für die Abgabe = for the submission

Is the word order fixed, or could I say something like Jede kleine Verbesserung macht uns sicherer im Text für die Abgabe?

German word order is fairly flexible, but not everything sounds natural.

The original:

Jede kleine Verbesserung im Text macht uns sicherer für die Abgabe.

Possible variations (still natural):

Jede kleine Verbesserung im Text macht uns für die Abgabe sicherer.
Im Text macht jede kleine Verbesserung uns sicherer für die Abgabe. (more emphasis on im Text)

Your version:

Jede kleine Verbesserung macht uns sicherer im Text für die Abgabe.

is understandable, but sounds a bit awkward, because sicherer im Text suggests we ourselves are more sure in the text, which is less idiomatic. The original clearly connects Verbesserung with im Text, and uns with sicherer.

So it’s best to keep im Text close to Verbesserung, and sicherer close to uns.