Quick Answer
The English mistakes that hurt tech candidates most are small and fixable: plural uncountable nouns (“informations”, “feedbacks”), present tense with “since”, missing articles, false friends such as “actual” for “current”, mispronounced terms like cache and queue, and numbers that are easy to mishear. Below are 20 our coaches correct again and again, each with the wrong version, the fix, and why an interviewer notices.
⚡ Quick Stats
Where This List Comes From
Mockly's two coaches, Tom and Sophie, are data engineers who teach interview English. Between them they have taught about 2,700 lessons, mostly to software engineers, data engineers and data analysts preparing for interviews at international companies. This list is the set of corrections that come up again and again in those sessions.
Insight
This is coaching experience, not a statistical survey. We have not ranked the mistakes by frequency; they are grouped by type so you can check yourself quickly.
This list is about the language itself: words, grammar, pronunciation and numbers. For mistakes in how you build an answer, such as over-explaining or saying “we” instead of “I”, read 10 English mistakes that cost non-native speakers the offer.
Quick Reference: All 20
| # | Mistake | Say instead |
|---|---|---|
| 1 | Uncountable nouns with -s | “Thanks for the feedback. I gathered some information about the software.” |
| 2 | Present tense with “since” and “for” | “I have worked here since 2021.” |
| 3 | Past achievements in the present tense | “Last year I migrated the pipeline and reduced the cost by 30%.” |
| 4 | Missing or extra articles | “I designed a system that sends notifications to the app's users.” |
| 5 | Wrong prepositions after common verbs | “It depends on the load.” |
| 6 | Question word order inside a sentence | “Can you tell me what the expected traffic is?” |
| 7 | “Actual” when you mean “current” | “Our current architecture has three services.” |
| 8 | “Eventually” when you mean “possibly” | “If needed, we could add a cache.” |
| 9 | “Realise” when you mean “carry out” | “I carried out the migration to Kubernetes.” |
| 10 | Make vs do, say vs tell | “Can I ask a question?” |
| 11 | “I have a doubt” for a question | “I have a question about the requirements.” |
| 12 | “Interesting” vs “interested”, “I'm agree” | “I am very interested in this role.” |
| 13 | “A data” and “datas” | “We store the data in S3.” |
| 14 | Mispronounced core terms | cache = “cash”, queue = “cue”, suite = “sweet”, width = “wid” + “th” |
| 15 | Stress on the wrong syllable | com-PO-nent, a-NAL-y-sis, de-VEL-op, AL-go-ri-thm, AR-chi-tect |
| 16 | Translated tech idioms | “We deployed it to production.” |
| 17 | Vague hedging on technical choices | “I'd use Kafka here, because we need replay. The trade-off is operational cost.” |
| 18 | Thirteen vs thirty, fifteen vs fifty | THIR-ty for 30, thir-TEEN for 13, and add a check: “thirty, three-zero”. |
| 19 | Percent vs percentage points, “on” vs “by” | “Conversion increased by 20%, from 10% to 12%.” or “by 2 percentage points”. |
| 20 | Decimals and large numbers | “One point five million users” |
Grammar (1–6)
1. Uncountable nouns with -s
✗ “Thanks for the feedbacks. I gathered some informations about the softwares.”
✓ “Thanks for the feedback. I gathered some information about the software.”
Feedback, information, software, advice, equipment and research have no plural. If you need to count them, say “two pieces of feedback” or “three tools”. Interviewers hear this one in the first minute.
2. Present tense with “since” and “for”
✗ “I work here since 2021.” / “I am working on this team for two years.”
✓ “I have worked here since 2021.” / “I've been working on this team for two years.”
Something that started in the past and is still true needs the present perfect. In the self-introduction, this mistake comes early and sets the tone.
3. Past achievements in the present tense
✗ “Last year I migrate the pipeline and reduce the cost.”
✓ “Last year I migrated the pipeline and reduced the cost by 30%.”
Without past tense, the interviewer cannot tell what you did from what you do in general. Say the -ed clearly: “migrated” has three syllables, “fixed” has one.
4. Missing or extra articles
✗ “I designed system that sends notifications to the users of app.”
✓ “I designed a system that sends notifications to the app's users.”
Use “a” the first time you mention one thing, “the” when the listener knows which one. Speakers of Slavic languages, Chinese and Hindi often drop articles; in a design answer it makes you sound less certain than you are.
5. Wrong prepositions after common verbs
✗ “It depends of the load.” / “We discussed about the API.” / “I was responsible of the release.”
✓ “It depends on the load.” / “We discussed the API.” / “I was responsible for the release.”
These are word-for-word translations. “Depends on”, “responsible for”, “discuss” with no preposition, and “interested in” are worth memorising as single units.
6. Question word order inside a sentence
✗ “Can you tell me what is the expected traffic?”
✓ “Can you tell me what the expected traffic is?” or simply “What's the expected traffic?”
Clarifying questions are scored in coding and design rounds. The short direct question is always correct and sounds confident.
Word choice and false friends (7–12)
7. “Actual” when you mean “current”
✗ “Our actual architecture has three services.”
✓ “Our current architecture has three services.”
In English, “actual” means “real”, not “present”. This false friend (actuel, aktuell, actual, attuale) can make the interviewer think you are contrasting with a fake architecture.
8. “Eventually” when you mean “possibly”
✗ “Eventually we could add a cache.” (meaning “if needed”)
✓ “If needed, we could add a cache.” / “Possibly we could add a cache.”
“Eventually” means “in the end, after some time”. Keep it for “eventual consistency”, which is correct. Otherwise the interviewer hears a plan, not an option.
9. “Realise” when you mean “carry out”
✗ “I realised the migration to Kubernetes.”
✓ “I carried out the migration to Kubernetes.” / “I led the migration.”
“Realise” means “understand suddenly”. In an ownership story, choose a strong verb: led, built, shipped, migrated, owned.
10. Make vs do, say vs tell
✗ “Can I do a question?” / “I did a mistake.” / “He said me to wait.”
✓ “Can I ask a question?” / “I made a mistake.” / “He told me to wait.”
You ask a question, make a mistake, make a decision, do a review. You tell someone something; you say something to someone.
11. “I have a doubt” for a question
✗ “I have a doubt about the requirements.”
✓ “I have a question about the requirements.” / “Can I check one requirement?”
In many varieties of English “doubt” means you think something is wrong. To an interviewer from the US or UK, it can sound as if you are challenging the problem.
12. “Interesting” vs “interested”, “I'm agree”
✗ “I am very interesting in this role.” / “Yes, I'm agree.”
✓ “I am very interested in this role.” / “Yes, I agree.”
“Interesting” describes the role; “interested” describes you. “Agree” is a verb and needs no “am”. Both often appear in the “why this company” answer.
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13. “A data” and “datas”
✗ “We store the datas in S3.” / “Each data has a timestamp.”
✓ “We store the data in S3.” / “Each record (or data point) has a timestamp.”
In tech English, treat “data” as uncountable: “the data is”. For one item, say “a record”, “a row”, “an event” or “a data point”.
14. Mispronounced core terms
✗ “cash-AY”, “KEW-ee-oo”, “s-WEET-ay”
✓ cache = “cash”, queue = “cue”, suite = “sweet”, width = “wid” + “th”
If the interviewer does not recognise a word, they lose the design. “SQL” can be “S-Q-L” or “sequel”; both are fine, so pick one and stay consistent.
15. Stress on the wrong syllable
✗ “COM-po-nent”, “a-na-LY-sis”, “DE-ve-lop”, “al-go-RI-thm”
✓ com-PO-nent, a-NAL-y-sis, de-VEL-op, AL-go-ri-thm, AR-chi-tect
English listeners recognise words by their stress. With the wrong stress, even a word you pronounce perfectly can be missed.
16. Translated tech idioms
✗ “We put it in production.” / “The service fell.”
✓ “We deployed it to production.” / “We shipped it.” / “The service went down.”
Literal translations usually make sense, but sound unusual. Learn the phrases engineers actually say: deploy, roll back, go down, spin up, hit a limit.
17. Vague hedging on technical choices
✗ “Maybe we can maybe use Kafka, I think, if it is OK.”
✓ “I'd use Kafka here, because we need replay. The trade-off is operational cost.”
Some hedging is polite. Three hedges in one sentence sound like you do not know. State the choice, then the reason, then the trade-off. More on this in the 10 mistakes guide linked above.
Numbers (18–20)
18. Thirteen vs thirty, fifteen vs fifty
✗ “About thir-TEE thousand requests” (meaning 30,000)
✓ THIR-ty for 30, thir-TEEN for 13, and add a check: “thirty, three-zero”.
In a capacity estimate, this is a 2x error that nobody notices until the end. See thirteen vs thirty.
19. Percent vs percentage points, “on” vs “by”
✗ “Conversion increased on 20%, from 10% to 12%.”
✓ “Conversion increased by 20%, from 10% to 12%.” or “by 2 percentage points”.
Going from 10% to 12% is 2 percentage points, or a 20% increase. Data and product interviewers notice the difference, and the preposition is “by”.
20. Decimals and large numbers
✗ “One comma five million users” / “ten thousands users” / “three milliards”
✓ “One point five million users” / “ten thousand users” / “three billion”
English uses a point for decimals and no plural on hundred, thousand or million after a number. “Milliard” is not used in English; say “billion”.
How to Fix Them Before Your Interview
- Record one real answer. Answer “Tell me about yourself” and one technical question out loud, on your phone. Listen back with this list open.
- Count, don't just notice. Mark each mistake you hear. Most people find two or three that repeat. Those are your list.
- Write the correct sentence. Not the rule, the sentence you will actually say: “I have worked here since 2021.”
- Say it ten times. Fluency comes from your mouth, not your notes. Repeat the corrected sentences until they feel normal.
- Test under pressure. Mistakes come back when you are nervous. Practise with someone who interrupts you, as an interviewer would.
For phrases to use instead, see 100 English phrases for job interviews. For thinking out loud in coding rounds, see how to explain code out loud in English.
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