Beginner
Code Comments
#todo
#fixme
TODO / FIXME / HACK Comments
6 exercises — write TODO, FIXME, HACK, and NOTE comments professionally, with owners, ticket references, and clear context.
0 / 26 completed
1 / 26
Which is the most professionally useful way to write a `TODO` comment?
A high-quality TODO comment includes: (1) an owner (or team) —
Formula:
Bare "TODO" with no context becomes permanent, unowned debt — searchable but meaningless. A well-written TODO is nearly as useful as a proper ticket, and often gets picked up faster because it's visible directly in the code path.
TODO(alex), (2) a specific description of what needs to happen, (3) a tracking reference (ticket number) when the work is non-trivial, and (4) context on why it's acceptable to defer right now.Formula:
// TODO(owner): [specific action] once/when [condition] — [current risk/impact].Bare "TODO" with no context becomes permanent, unowned debt — searchable but meaningless. A well-written TODO is nearly as useful as a proper ticket, and often gets picked up faster because it's visible directly in the code path.
2 / 26
What is the correct professional use of a `FIXME` comment, as distinct from `TODO`?
The conventional distinction: `TODO` marks planned, not-yet-done work (often a feature or improvement); `FIXME` marks a known defect in code that already exists and is currently running — something actively wrong, not just incomplete. Many linters and static analysis tools treat `FIXME` with higher urgency than `TODO` for exactly this reason.
Formula:
Using the two markers correctly helps automated tooling and human reviewers triage code health accurately — grepping for `FIXME` should surface real bugs, not just future feature ideas.
Formula:
// FIXME: [specific incorrect behaviour] — [condition that triggers it] — [ticket, if tracked].Using the two markers correctly helps automated tooling and human reviewers triage code health accurately — grepping for `FIXME` should surface real bugs, not just future feature ideas.
3 / 26
You need to write a `HACK` comment for a workaround you know is not the "proper" fix. Which is correctly written?
A `HACK` comment should explain (1) what the workaround does, (2) why the "proper" solution isn't used (external constraint, time pressure, upstream bug), and (3) ideally, what would trigger removing it. This turns an apology into actionable information for the next engineer who encounters the code.
Formula:
Being explicit about the trade-off (rather than just "this is hacky, sorry") helps future maintainers judge whether the hack is still necessary and gives them the context to remove it safely when circumstances change.
Formula:
// HACK: [what it does] to work around [specific constraint/bug]. [Removal condition, if known].Being explicit about the trade-off (rather than just "this is hacky, sorry") helps future maintainers judge whether the hack is still necessary and gives them the context to remove it safely when circumstances change.
4 / 26
What is the correct use of a `NOTE` comment marker, distinct from `TODO`/`FIXME`/`HACK`?
`NOTE` is the marker for important, non-obvious context that isn't actionable debt (unlike TODO/FIXME/HACK) but that a future reader genuinely needs to know — an invariant, a non-obvious dependency, or a warning about a subtle behaviour.
Formula:
The four markers (TODO/FIXME/HACK/NOTE) form a useful, greppable vocabulary: TODO = planned work, FIXME = known bug, HACK = intentional workaround, NOTE = important context. Using them consistently makes a codebase's debt and caveats searchable in one command (`grep -rn "TODO\|FIXME\|HACK"`).
Formula:
// NOTE: [important context or invariant that isn't obvious from the code alone].The four markers (TODO/FIXME/HACK/NOTE) form a useful, greppable vocabulary: TODO = planned work, FIXME = known bug, HACK = intentional workaround, NOTE = important context. Using them consistently makes a codebase's debt and caveats searchable in one command (`grep -rn "TODO\|FIXME\|HACK"`).
5 / 26
A code review comment says: "This TODO has no owner and no ticket — it's been here for 2 years." What is the correct professional response?
Stale, unowned TODOs are a common code smell. The professional response acknowledges the gap and commits to one of two concrete actions: formalise it (create a ticket, assign an owner) if it's still relevant, or remove it if the underlying concern has been resolved or is no longer valid. Leaving it as ambiguous, unowned debt is the wrong outcome either way.
Formula:
Some teams enforce this with a CI check that fails on TODOs without a ticket reference, precisely to prevent comments like this from silently aging for years.
Formula:
"Good catch — I'll [create a ticket and assign an owner / remove the comment] since [reasoning]."Some teams enforce this with a CI check that fails on TODOs without a ticket reference, precisely to prevent comments like this from silently aging for years.
6 / 26
Why is it considered bad practice to use `TODO`/`FIXME` comments as a substitute for an actual issue tracker for significant work?
In-code markers are excellent for local, code-adjacent context ("this specific line needs revisiting") but poor for project management — they lack assignment, prioritisation, status, discoverability outside the file, and reporting. The professional pattern is to use both together: a short in-code marker referencing a ticket number, with the ticket carrying the full tracking metadata.
Useful phrase: "Let's keep the comment for local context but file a ticket for visibility and prioritisation — comments alone are easy to lose track of." This hybrid approach gets the benefits of both: immediate visibility in the code, and proper tracking in the backlog.
Useful phrase: "Let's keep the comment for local context but file a ticket for visibility and prioritisation — comments alone are easy to lose track of." This hybrid approach gets the benefits of both: immediate visibility in the code, and proper tracking in the backlog.
7 / 26
Sarah, during a code review of the PaymentService, flagged this comment: 'This FIXME is referencing a deprecated API endpoint. It's been identified as a high-risk area for future breakage and should be addressed ASAP.' Which of the following best describes Sarah's intent with this comment?
A) To politely suggest
Sarah should investigate the API endpoint later.
B) To formally document a known issue requiring immediate attention due to potential instability and impact.
C) To offer a vague suggestion that the code could be improved for clarity.
D) To request that Sarah update the ticket with more details about the problem.This scenario highlights the *purpose* of a `FIXME` comment. Unlike a `TODO`, which is often a less urgent reminder, a `FIXME` signals a critical issue – in this case, a deprecated API that poses a significant risk. The correct answer reflects this urgency and formal documentation intent; options A, C, and D misrepresent the seriousness of a `FIXME` and its role within a code review context.
8 / 26
John is reviewing a new feature for the OrderProcessingService. He finds this comment in the code: `// FIXME: This logic handles refunds incorrectly when the order status is 'Cancelled'. It's causing intermittent issues for users and has been flagged as a priority one bug.
Which of the following best describes John's intent with this comment?The key here is understanding the context of a `FIXME` comment. Unlike a `TODO` which often represents an unfinished task or area for future exploration, a `FIXME` *specifically* highlights a known problem that requires immediate attention. Option A misinterprets the urgency implied by 'priority one bug' and 'intermittent issues'. Option C is too vague; it doesn't convey the seriousness of the situation. Option D incorrectly frames the comment as a request for a new ticket when the existing comment already serves as a critical alert. Therefore, option B accurately reflects John's intent – to document and prioritize a high-impact issue.
9 / 26
David is reviewing a new feature for the UserProfileService. He encounters this comment within a function: `// FIXME: This calculates user age based on birthdate. It's inaccurate by up to 3 days due to timezone differences and inconsistent date formats across our legacy systems. We need to migrate to a more robust solution.`
Which of the following best describes David's intent with this comment?
The
FIXME comment in this case is appropriately highlighting a known defect. It clearly articulates the problem (inaccurate age calculation) and provides enough context to understand its origin (timezone differences and inconsistent date formats). Option A is incorrect because an inaccurate calculation *does* impact users. Options C and D are less precise; while investigation might be needed, the comment already conveys the severity and reason for concern, and a `FIXME` isn't meant for exploratory investigation.10 / 26
During a code review of a new microservice, Liam notices the following comment: `// FIXME: This function performs a complex calculation that's impacting performance. It's been identified as a bottleneck and should be optimized for production environments. Consider using caching or alternative algorithms.` Which of the following best reflects Liam's intended action and the *purpose* of this `FIXME` comment?
The `FIXME` comment in this scenario isn't about general code improvement or design discussions. It's specifically highlighting a performance bottleneck – something that directly impacts service stability and user experience. The phrase 'critical performance issue' and 'should be optimized for production environments' clearly indicates the urgency and severity of the problem, signaling that action needs to be taken immediately, making option B the correct choice. Options A, C, and D misinterpret the purpose of a `FIXME` comment – it's not a gentle suggestion or purely informational.
11 / 26
You're reviewing a PR for the AuthenticationService. The developer has added this `FIXME` comment to a function that handles password resets:
// FIXME: This password reset logic uses a simple string manipulation approach. It's vulnerable to brute-force attacks and doesn't adhere to our security best practices. A more robust solution is required.
Which of the following best describes the developer's intent with this comment, and what action should you recommend as the *next* step?
This `FIXME` isn't just about aesthetics; it flags a significant security risk. The developer correctly identifies a vulnerability (brute-force attacks) and emphasizes the need for a more robust solution – highlighting that the current code is not meeting required standards. Therefore, prioritizing remediation of this vulnerability is the appropriate next step.
12 / 26
Sarah, during a code review of the PaymentService, flagged this comment: 'This FIXME is referencing a deprecated API endpoint. It's been identified as a high-risk area for future breakage and should be addressed ASAP.' Which of the following best describes Sarah's intent with this comment?
A) To politely suggest
Sarah should investigate the API endpoint later.
B) To formally document a known issue requiring immediate attention due to potential instability and impact.
C) To offer a vague suggestion that the code could be improved for clarity.
D) To request that Sarah update the ticket with more details about the problem.This scenario highlights the *purpose* of a `FIXME` comment. Unlike a `TODO`, which is often a less urgent reminder, a `FIXME` signals a critical issue – in this case, a deprecated API that poses a significant risk. The correct answer reflects this urgency and formal documentation intent; options A, C, and D misrepresent the seriousness of a `FIXME` and its role within a code review context.
13 / 26
John is reviewing a new feature for the OrderProcessingService. He finds this comment in the code: `// FIXME: This logic handles refunds incorrectly when the order status is 'Cancelled'. It's causing intermittent issues for users and has been flagged as a priority one bug.
Which of the following best describes John's intent with this comment?The key here is understanding the context of a `FIXME` comment. Unlike a `TODO` which often represents an unfinished task or area for future exploration, a `FIXME` *specifically* highlights a known problem that requires immediate attention. Option A misinterprets the urgency implied by 'priority one bug' and 'intermittent issues'. Option C is too vague; it doesn't convey the seriousness of the situation. Option D incorrectly frames the comment as a request for a new ticket when the existing comment already serves as a critical alert. Therefore, option B accurately reflects John's intent – to document and prioritize a high-impact issue.
14 / 26
David is reviewing a new feature for the UserProfileService. He encounters this comment within a function: `// FIXME: This calculates user age based on birthdate. It's inaccurate by up to 3 days due to timezone differences and inconsistent date formats across our legacy systems. We need to migrate to a more robust solution.`
Which of the following best describes David's intent with this comment?
The
FIXME comment in this case is appropriately highlighting a known defect. It clearly articulates the problem (inaccurate age calculation) and provides enough context to understand its origin (timezone differences and inconsistent date formats). Option A is incorrect because an inaccurate calculation *does* impact users. Options C and D are less precise; while investigation might be needed, the comment already conveys the severity and reason for concern, and a `FIXME` isn't meant for exploratory investigation.15 / 26
During a code review of a new microservice, Liam notices the following comment: `// FIXME: This function performs a complex calculation that's impacting performance. It's been identified as a bottleneck and should be optimized for production environments. Consider using caching or alternative algorithms.` Which of the following best reflects Liam's intended action and the *purpose* of this `FIXME` comment?
The `FIXME` comment in this scenario isn't about general code improvement or design discussions. It's specifically highlighting a performance bottleneck – something that directly impacts service stability and user experience. The phrase 'critical performance issue' and 'should be optimized for production environments' clearly indicates the urgency and severity of the problem, signaling that action needs to be taken immediately, making option B the correct choice. Options A, C, and D misinterpret the purpose of a `FIXME` comment – it's not a gentle suggestion or purely informational.
16 / 26
You're reviewing a PR for the AuthenticationService. The developer has added this `FIXME` comment to a function that handles password resets:
// FIXME: This password reset logic uses a simple string manipulation approach. It's vulnerable to brute-force attacks and doesn't adhere to our security best practices. A more robust solution is required.
Which of the following best describes the developer's intent with this comment, and what action should you recommend as the *next* step?
This `FIXME` isn't just about aesthetics; it flags a significant security risk. The developer correctly identifies a vulnerability (brute-force attacks) and emphasizes the need for a more robust solution – highlighting that the current code is not meeting required standards. Therefore, prioritizing remediation of this vulnerability is the appropriate next step.
17 / 26
Sarah, during a code review of the PaymentService, flagged this comment: 'This FIXME is referencing a deprecated API endpoint. It's been identified as a high-risk area for future breakage and should be addressed ASAP.' Which of the following best describes Sarah's intent with this comment?
A) To politely suggest
Sarah should investigate the API endpoint later.
B) To formally document a known issue requiring immediate attention due to potential instability and impact.
C) To offer a vague suggestion that the code could be improved for clarity.
D) To request that Sarah update the ticket with more details about the problem.This scenario highlights the *purpose* of a `FIXME` comment. Unlike a `TODO`, which is often a less urgent reminder, a `FIXME` signals a critical issue – in this case, a deprecated API that poses a significant risk. The correct answer reflects this urgency and formal documentation intent; options A, C, and D misrepresent the seriousness of a `FIXME` and its role within a code review context.
18 / 26
John is reviewing a new feature for the OrderProcessingService. He finds this comment in the code: `// FIXME: This logic handles refunds incorrectly when the order status is 'Cancelled'. It's causing intermittent issues for users and has been flagged as a priority one bug.
Which of the following best describes John's intent with this comment?The key here is understanding the context of a `FIXME` comment. Unlike a `TODO` which often represents an unfinished task or area for future exploration, a `FIXME` *specifically* highlights a known problem that requires immediate attention. Option A misinterprets the urgency implied by 'priority one bug' and 'intermittent issues'. Option C is too vague; it doesn't convey the seriousness of the situation. Option D incorrectly frames the comment as a request for a new ticket when the existing comment already serves as a critical alert. Therefore, option B accurately reflects John's intent – to document and prioritize a high-impact issue.
19 / 26
David is reviewing a new feature for the UserProfileService. He encounters this comment within a function: `// FIXME: This calculates user age based on birthdate. It's inaccurate by up to 3 days due to timezone differences and inconsistent date formats across our legacy systems. We need to migrate to a more robust solution.`
Which of the following best describes David's intent with this comment?
The
FIXME comment in this case is appropriately highlighting a known defect. It clearly articulates the problem (inaccurate age calculation) and provides enough context to understand its origin (timezone differences and inconsistent date formats). Option A is incorrect because an inaccurate calculation *does* impact users. Options C and D are less precise; while investigation might be needed, the comment already conveys the severity and reason for concern, and a `FIXME` isn't meant for exploratory investigation.20 / 26
During a code review of a new microservice, Liam notices the following comment: `// FIXME: This function performs a complex calculation that's impacting performance. It's been identified as a bottleneck and should be optimized for production environments. Consider using caching or alternative algorithms.` Which of the following best reflects Liam's intended action and the *purpose* of this `FIXME` comment?
The `FIXME` comment in this scenario isn't about general code improvement or design discussions. It's specifically highlighting a performance bottleneck – something that directly impacts service stability and user experience. The phrase 'critical performance issue' and 'should be optimized for production environments' clearly indicates the urgency and severity of the problem, signaling that action needs to be taken immediately, making option B the correct choice. Options A, C, and D misinterpret the purpose of a `FIXME` comment – it's not a gentle suggestion or purely informational.
21 / 26
You're reviewing a PR for the AuthenticationService. The developer has added this `FIXME` comment to a function that handles password resets:
// FIXME: This password reset logic uses a simple string manipulation approach. It's vulnerable to brute-force attacks and doesn't adhere to our security best practices. A more robust solution is required.
Which of the following best describes the developer's intent with this comment, and what action should you recommend as the *next* step?
This `FIXME` isn't just about aesthetics; it flags a significant security risk. The developer correctly identifies a vulnerability (brute-force attacks) and emphasizes the need for a more robust solution – highlighting that the current code is not meeting required standards. Therefore, prioritizing remediation of this vulnerability is the appropriate next step.
22 / 26
Sarah, during a code review of the PaymentService, flagged this comment: 'This FIXME is referencing a deprecated API endpoint. It's been identified as a high-risk area for future breakage and should be addressed ASAP.' Which of the following best describes Sarah's intent with this comment?
A) To politely suggest
Sarah should investigate the API endpoint later.
B) To formally document a known issue requiring immediate attention due to potential instability and impact.
C) To offer a vague suggestion that the code could be improved for clarity.
D) To request that Sarah update the ticket with more details about the problem.This scenario highlights the *purpose* of a `FIXME` comment. Unlike a `TODO`, which is often a less urgent reminder, a `FIXME` signals a critical issue – in this case, a deprecated API that poses a significant risk. The correct answer reflects this urgency and formal documentation intent; options A, C, and D misrepresent the seriousness of a `FIXME` and its role within a code review context.
23 / 26
John is reviewing a new feature for the OrderProcessingService. He finds this comment in the code: `// FIXME: This logic handles refunds incorrectly when the order status is 'Cancelled'. It's causing intermittent issues for users and has been flagged as a priority one bug.
Which of the following best describes John's intent with this comment?The key here is understanding the context of a `FIXME` comment. Unlike a `TODO` which often represents an unfinished task or area for future exploration, a `FIXME` *specifically* highlights a known problem that requires immediate attention. Option A misinterprets the urgency implied by 'priority one bug' and 'intermittent issues'. Option C is too vague; it doesn't convey the seriousness of the situation. Option D incorrectly frames the comment as a request for a new ticket when the existing comment already serves as a critical alert. Therefore, option B accurately reflects John's intent – to document and prioritize a high-impact issue.
24 / 26
David is reviewing a new feature for the UserProfileService. He encounters this comment within a function: `// FIXME: This calculates user age based on birthdate. It's inaccurate by up to 3 days due to timezone differences and inconsistent date formats across our legacy systems. We need to migrate to a more robust solution.`
Which of the following best describes David's intent with this comment?
The
FIXME comment in this case is appropriately highlighting a known defect. It clearly articulates the problem (inaccurate age calculation) and provides enough context to understand its origin (timezone differences and inconsistent date formats). Option A is incorrect because an inaccurate calculation *does* impact users. Options C and D are less precise; while investigation might be needed, the comment already conveys the severity and reason for concern, and a `FIXME` isn't meant for exploratory investigation.25 / 26
During a code review of a new microservice, Liam notices the following comment: `// FIXME: This function performs a complex calculation that's impacting performance. It's been identified as a bottleneck and should be optimized for production environments. Consider using caching or alternative algorithms.` Which of the following best reflects Liam's intended action and the *purpose* of this `FIXME` comment?
The `FIXME` comment in this scenario isn't about general code improvement or design discussions. It's specifically highlighting a performance bottleneck – something that directly impacts service stability and user experience. The phrase 'critical performance issue' and 'should be optimized for production environments' clearly indicates the urgency and severity of the problem, signaling that action needs to be taken immediately, making option B the correct choice. Options A, C, and D misinterpret the purpose of a `FIXME` comment – it's not a gentle suggestion or purely informational.
26 / 26
You're reviewing a PR for the AuthenticationService. The developer has added this `FIXME` comment to a function that handles password resets:
// FIXME: This password reset logic uses a simple string manipulation approach. It's vulnerable to brute-force attacks and doesn't adhere to our security best practices. A more robust solution is required.
Which of the following best describes the developer's intent with this comment, and what action should you recommend as the *next* step?
This `FIXME` isn't just about aesthetics; it flags a significant security risk. The developer correctly identifies a vulnerability (brute-force attacks) and emphasizes the need for a more robust solution – highlighting that the current code is not meeting required standards. Therefore, prioritizing remediation of this vulnerability is the appropriate next step.
Frequently Asked Questions
What will I practice in "TODO/FIXME/HACK Comments — Code Comments Exercise"?
This is a Code Comments exercise set. It walks through 26 scenario-based multiple-choice questions built around real usage of Code Comments terminology that IT professionals encounter on the job.
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