Path 83 · The request observatory · Intermediate
Locate the failure before changing the code.
A guided, practical route through http api debugging.
What you will be able to do
Diagnose a local HTTP API from request and response evidence, distinguish transport from application failures and write a reproducible bug report.
Plan about 8h 17m in total. Reading and practice are editorial estimates; video runtimes come from public provider metadata. Your pace will vary.
Before you begin
Check your starting point
What you need
Basic JavaScript and command-line use. Node.js and a local browser or curl are sufficient.
The selected public provider lessons are free to view. The original case can be completed with paper, a text editor or freely available local tools. Paid exams, certificates, subscriptions and optional provider software are not required for this project.
Completing this WikiFree path does not award a provider certificate. Any provider assessment, account requirement or credential must be checked separately on its official page.
Three readiness questions
Does 404 mean the network failed?
No. An HTTP server returned a response.
Does a 200 prove the response data are correct?
No.
What makes a bug reproducible?
An exact request, expected result and observed response.
Use a workable pace
At 5 hours per week, allow about 2 weeks. Start with Stage 1, continue in order and reserve 2h for the capstone. If a gate fails, use its repair step before advancing. At another weekly budget, divide 497 estimated minutes by your available weekly minutes and round up.
Keep a small evidence folder. A checked box means you reviewed your output; it is not a certificate or proof that a provider lesson was watched.
The working case
Four requests, four clear outcomes
A local-only fixture exposes GET /health and GET /items. Requests to an unknown path return 404; an unsupported method on a known path returns 405. The exercise binds to loopback and contains no authentication or real user data.
| Request | Expected status | Meaning |
|---|---|---|
| GET /health | 200 | healthy fixture |
| GET /items | 200 | two sample items |
| GET /missing | 404 | unknown route |
| POST /items | 405 | unsupported method |
The table and explanations preserve the essential case information when the diagram is unavailable.
Your route
Five outputs, then a final handoff
- 01Locate the protocol layerDiagnostic map
About 1h 42m including assigned learning and practice. - 02Run the local fixtureLocal request log
About 1h 10m including assigned learning and practice. - 03Test negative casesFailure-case evidence
About 1h 20m including assigned learning and practice. - 04Trace and repair a mismatchBug report and repair note
About 1h 15m including assigned learning and practice. - 05Package a debugging runbookHTTP debugging pack
About 50m including assigned learning and practice. - FINALCapstone reviewCombine the evidence into one inspectable handoff.
About 2h .
0 of 6 outputs checked. JavaScript adds browser-only progress saving.
The complete lesson and all downloads remain available. Use the printable project workbook to track your progress.
Use the minimum useful source material
The courses behind this route
Free Computer Networking Course by Google
The published networking lesson explains transport and application layers; current MDN HTTP documentation supplies protocol-specific context.
Selected material only; this path does not claim completion of the entire provider course.
Course publication and selected public lesson metadata were checked on 13 October 2026. This is not a claim of full video playback, provider-course completion or permanent availability. Recheck the linked source if a lesson changes.
Learn, make, inspect
The five-stage workshop
Locate the protocol layer
Video 42m · reading budget 0m · original practice about 1h .
A connection problem and an HTTP error occur at different layers. If a server returns a status, a connection and response have already happened. Record method, URL, headers, status and body before guessing a cause. The networking lesson supplies layer context; official HTTP documentation fills the protocol details.
Watch these selected lessons
Do the work
Classify connection refused, 404 and malformed JSON by failure layer.
Save this output
Diagnostic map
Pass the review gate
An HTTP error is not mislabeled as DNS failure.
If you need another attempt
Start from the evidence actually received.
Run the local fixture
Video 0m · reading budget 0m · original practice about 1h 10m.
Bind the example to 127.0.0.1 and use a chosen local port. Avoid publishing it to the internet for this exercise. Keep endpoints small and deterministic. A health response says this fixture handled a request; it does not certify a database or dependent service that the fixture does not have.
Original application stage. Use your preceding outputs and the supplied case; there is no additional required provider lesson.
Do the work
Start the server and request /health and /items.
Save this output
Local request log
Pass the review gate
Both expected 200 responses have the documented JSON shape.
If you need another attempt
Check content type and body as well as status.
Test negative cases
Video 0m · reading budget 0m · original practice about 1h 20m.
Negative cases reveal routing and method behavior. A 405 response should identify supported methods for the resource. A 404 should not accidentally return an unrelated success page. Keep error bodies consistent enough for clients to understand while avoiding unnecessary internal details.
Original application stage. Use your preceding outputs and the supplied case; there is no additional required provider lesson.
Do the work
Request an unknown route and POST to /items.
Save this output
Failure-case evidence
Pass the review gate
Statuses are 404 and 405; the latter advertises GET.
If you need another attempt
Compare the exact path and method before editing code.
Trace and repair a mismatch
Video 0m · reading budget 0m · original practice about 1h 15m.
Change one fixture expectation in a test copy and use the request log to identify the mismatch. A good repair addresses the contract rather than merely changing the test until it passes. Preserve the original expected behavior and explain why the implementation or specification should change.
Original application stage. Use your preceding outputs and the supplied case; there is no additional required provider lesson.
Do the work
Introduce a wrong item count in a test, diagnose it and restore the contract.
Save this output
Bug report and repair note
Pass the review gate
The report includes a copyable local request and observed response.
If you need another attempt
Avoid screenshots without the request details needed to reproduce the issue.
Package a debugging runbook
Video 0m · reading budget 0m · original practice about 50m.
A runbook should proceed from connectivity to status, headers and payload. Include how to stop the local server and rerun checks. Do not include secrets in logs. This fixture intentionally omits authentication, persistence and production hardening so the protocol evidence stays easy to inspect.
Original application stage. Use your preceding outputs and the supplied case; there is no additional required provider lesson.
Do the work
Write a five-step diagnostic runbook and retain the test output.
Save this output
HTTP debugging pack
Pass the review gate
A reviewer can reproduce the four cases on loopback.
If you need another attempt
State the local-only scope next to the start command.
Make the result inspectable
Your final project
Deliver the fixture, four request checks, one bug report and the diagnostic runbook. Demonstrate that a failed connection is reported differently from a returned 404.
The ZIP includes synthetic input data, a project workbook, worked reference, evidence log, scoring rubric and case-specific materials. Code projects include source and clearly stated local execution requirements.
Use one consistent rubric
| Criterion | Maximum | Evidence |
|---|---|---|
| Evidence and correctness | 30 | Calculations, source use and results match the supplied case; limitations are honest. |
| Required artifacts | 30 | All five stage outputs and the capstone handoff are present and inspectable. |
| Reasoning and decisions | 20 | Choices, assumptions, alternatives and the case-specific critical condition are explained. |
| Reproducibility | 10 | A reviewer can follow the stated steps and distinguish expected from observed results. |
| Clear communication | 10 | Labels, units, structure and evidence references make the work easy to review. |
Score at least 80/100, supply every required artifact, and satisfy the path-specific critical condition. Rework missing evidence before marking complete.
The critical condition
Tests remain local and response status is not treated as proof of every payload or dependency.
Compare with a worked reference
The four case statuses are 200, 200, 404 and 405. A 404 is an application-level route response, while a refused connection produces no HTTP status from this server. The /items body contains exactly two synthetic items.
Know the boundary
This is HTTP diagnosis for a local fixture, not a deployed API or authorization test against a third-party system.
Questions before you finish
Do I need to finish every source course?
No. This path names selected lessons or reading sections. Complete the full provider course only if it supports your wider goal. The path does not claim equivalence to that course.
How do I know when to advance?
Use the output and review gate in each stage. If evidence is missing or a result conflicts with the case, follow the repair step and retry before advancing.
Can I do the project without paid software?
The selected public provider lessons are free to view. The original case can be completed with paper, a text editor or freely available local tools. Paid exams, certificates, subscriptions and optional provider software are not required for this project.
What does my checklist prove?
It records your own review in this browser only. It does not verify viewing, skill, a provider credential or a real-world deployment.
What if a lesson or tool changes?
Use the linked course and provider page to inspect current availability. Record the change and revisit the relevant assignment; do not invent a replacement lesson or claim an unavailable activity was completed.
Questions & discussion
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