This skill ensures API endpoint reviews validate against OpenAPI specifications, verify complete test coverage per TESTING.md, and enforce SDK architecture patterns from ADVANCED.md.

Core principle: Cannot approve without validating every field against OpenAPI spec, verifying all 6 mandatory tests exist, and detecting breaking changes.

CRITICAL: Breaking changes detection is the HIGHEST PRIORITY review concern. Even perfect implementation must be blocked if it contains undisclosed breaking changes.

When to Use

Use when:

Reviewing PR that adds new API endpoint
Reviewing PR that modifies existing endpoint
Reviewing model class changes for API responses
Before approving any endpoint-related code

Do NOT use for:

Non-API code reviews (utilities, internal helpers)
Documentation-only changes
Test-only fixes (unless they affect API contract)

Review Workflow

digraph review_endpoint {
    "Start Review" [shape=doublecircle];
    "Identify endpoint being added/changed" [shape=box];
    "Check for BREAKING CHANGES" [shape=box, style=filled, fillcolor=yellow];
    "Breaking changes found?" [shape=diamond];
    "PR explicitly mentions breaking changes?" [shape=diamond];
    "BLOCK - Undisclosed breaking changes" [shape=box, style=filled, fillcolor=red];
    "Note: Requires major version" [shape=box];
    "Fetch OpenAPI spec" [shape=box];
    "Spec has endpoint?" [shape=diamond];
    "BLOCK - Request spec" [shape=box, style=filled, fillcolor=red];
    "Create validation checklist" [shape=box];
    "Validate ALL model fields vs spec" [shape=box];
    "All fields match?" [shape=diamond];
    "REQUEST CHANGES - Field mismatch" [shape=box, style=filled, fillcolor=orange];
    "Verify AbstractResources pattern used" [shape=box];
    "Pattern correct?" [shape=diamond];
    "REQUEST CHANGES - Wrong pattern" [shape=box, style=filled, fillcolor=orange];
    "Count test types" [shape=box];
    "All 6 tests present?" [shape=diamond];
    "REQUEST CHANGES - Missing tests" [shape=box, style=filled, fillcolor=orange];
    "Validate test quality per TESTING.md" [shape=box];
    "Tests follow strict rules?" [shape=diamond];
    "REQUEST CHANGES - Test quality issues" [shape=box, style=filled, fillcolor=orange];
    "APPROVE" [shape=box, style=filled, fillcolor=green];

    "Start Review" -> "Identify endpoint being added/changed";
    "Identify endpoint being added/changed" -> "Check for BREAKING CHANGES";
    "Check for BREAKING CHANGES" -> "Breaking changes found?";
    "Breaking changes found?" -> "PR explicitly mentions breaking changes?" [label="yes"];
    "Breaking changes found?" -> "Fetch OpenAPI spec" [label="no"];
    "PR explicitly mentions breaking changes?" -> "BLOCK - Undisclosed breaking changes" [label="no"];
    "PR explicitly mentions breaking changes?" -> "Note: Requires major version" [label="yes"];
    "Note: Requires major version" -> "Fetch OpenAPI spec";
    "Fetch OpenAPI spec" -> "Spec has endpoint?";
    "Spec has endpoint?" -> "BLOCK - Request spec" [label="no"];
    "Spec has endpoint?" -> "Create validation checklist" [label="yes"];
    "Create validation checklist" -> "Validate ALL model fields vs spec";
    "Validate ALL model fields vs spec" -> "All fields match?";
    "All fields match?" -> "REQUEST CHANGES - Field mismatch" [label="no"];
    "All fields match?" -> "Verify AbstractResources pattern used" [label="yes"];
    "Verify AbstractResources pattern used" -> "Pattern correct?";
    "Pattern correct?" -> "REQUEST CHANGES - Wrong pattern" [label="no"];
    "Pattern correct?" -> "Count test types" [label="yes"];
    "Count test types" -> "All 6 tests present?";
    "All 6 tests present?" -> "REQUEST CHANGES - Missing tests" [label="no"];
    "All 6 tests present?" -> "Validate test quality per TESTING.md" [label="yes"];
    "Validate test quality per TESTING.md" -> "Tests follow strict rules?";
    "Tests follow strict rules?" -> "REQUEST CHANGES - Test quality issues" [label="no"];
    "Tests follow strict rules?" -> "APPROVE" [label="yes"];
}

Step 0: Check for Breaking Changes (CRITICAL - DO THIS FIRST)

⚠️ INCREDIBLY IMPORTANT: Breaking changes detection is the HIGHEST PRIORITY concern in API reviews.

This check happens BEFORE all other validation. Even perfect code must be BLOCKED if it contains undisclosed breaking changes.

Why This Matters

Breaking changes in a public SDK:

Break every user's code that depends on changed APIs
Require major version bump (semantic versioning)
Require migration guides and announcements
Can block users from upgrading (stuck on old versions)
Damage trust if shipped without warning

Rule: Unless PR description EXPLICITLY mentions "breaking change" or "breaking changes", ANY detected breaking change MUST result in BLOCKED approval.

Breaking Changes Checklist

Compare git diff of public interfaces, classes, and methods. Check for:

Method Signature Changes (ALWAYS BREAKING)

Method renamed (even with better name)
Method removed (even if deprecated)
Parameters added/removed/reordered
Parameter types changed
Return type changed
Exception types in throws clause changed
Method moved to different class/interface

Field Changes in Public Models (ALWAYS BREAKING)

Public field removed
Public field renamed
Public getter/setter removed or renamed
Field type changed
Field nullability changed (required ↔ optional)

Access Modifier Changes (USUALLY BREAKING)

public → protected/private (removes access)
Interface method added (forces implementation)
Abstract method added to base class

Class/Interface Changes (ALWAYS BREAKING)

Class/interface removed
Class/interface renamed
Class moved to different package
Interface added to implements clause (forces contract)
Inheritance hierarchy changed

Exception Behavior Changes (SUBTLE BUT BREAKING)

Method throws new exception types
Method no longer throws documented exception
Exception hierarchy changed

How to Check

For each modified file in PR:

# Get list of modified public files
git diff --name-only origin/mainline...HEAD | grep -E '(Resources\.java|models/.*\.java)'

# For each file, check what changed
git diff origin/mainline...HEAD path/to/File.java

Look for:

Method signatures: Any change to public method name, parameters, return type
Field declarations: Any change to getter/setter names or return types
Class declarations: Changes to class name, implements, extends
Access modifiers: Changes from public to less accessible

Breaking Changes Detection Examples

Example 1: Method Rename

// OLD (mainline)
public TokenPaginatedResult<UserPlan> listUserPlans(long userId, String lastKey, Long maxItems)

// NEW (PR)
public TokenPaginatedResult<UserPlan> getUserPlans(long userId, String lastKey, Long maxItems)

BREAKING: Method name changed. All user code calling listUserPlans() breaks.

Example 2: Field Removal

// OLD
private Boolean isInternal;
public Boolean getIsInternal() { return isInternal; }

// NEW
// (field removed, getter removed)

BREAKING: Public getter removed. All user code calling getIsInternal() breaks.

Example 3: Return Type Change

// OLD
public List<Sheet> listSheets()

// NEW
public PagedResult<Sheet> listSheets()

BREAKING: Return type changed. User code assigning to List<Sheet> breaks.

Example 4: Parameter Addition (SEEMS safe, ACTUALLY breaking)

// OLD
public Report createReport(ReportDefinition definition)

// NEW
public Report createReport(ReportDefinition definition, Boolean validate)

BREAKING: New required parameter. All existing calls missing the parameter break.

PR Description Validation

After detecting breaking changes:

Read PR description/commit messages
Search for keywords: "breaking", "breaking change", "major version", "backwards incompatible"
Check if author explicitly acknowledges the breaking change

If breaking changes found AND not mentioned:

🚫 BLOCK APPROVAL

CRITICAL: This PR contains BREAKING CHANGES that are not disclosed in the PR description.

Breaking changes detected:
- [List each breaking change with file:line reference]

**This PR CANNOT be approved** unless:
1. PR description explicitly mentions "breaking change" or "breaking changes"
2. Justification provided for why breaking change is necessary
3. Planned for major version release (e.g., 4.0.0)
4. Migration path documented

Semantic versioning requires major version bump for ANY breaking change.

If breaking changes found AND mentioned:

⚠️ WARNING: Breaking Changes Detected

This PR contains breaking changes (acknowledged by author):
- [List each breaking change]

Before approval, verify:
- [ ] Planned for major version release (X.0.0)
- [ ] CHANGELOG updated with breaking change notice
- [ ] Migration guide created/updated
- [ ] Sufficient justification provided

Proceed with review of other aspects.

Common Rationalizations to REJECT

Excuse	Reality
"It's an improvement"	Improvements can be breaking. If it changes API surface, it's breaking.
"API changed, SDK should match"	SDK breaking changes are independent of API changes. Still breaking.
"It's technically compatible"	Behavior changes break user expectations. Still breaking.
"We deprecated it already"	Deprecation warns about future removal. Removal itself is breaking.
"Better name" / "More intuitive"	Renaming is breaking. No matter how much better.
"Only affects edge cases"	Any code breakage is breaking, regardless of how few users affected.
"Tests pass"	Tests don't represent all user code in the wild.
"We'll document it"	Documentation doesn't make breaking changes non-breaking.

When Breaking Changes Are Acceptable

Breaking changes ARE acceptable when:

Explicitly disclosed in PR description
Justified - clear reason why breaking change is necessary
Planned for major version release (X.0.0)
Documented - migration guide, CHANGELOG entry
Approved by maintainers for inclusion in next major release

But still must be FLAGGED in review as requiring major version.

Step 1: Fetch OpenAPI Specification

MANDATORY: Cannot review without spec.

For public endpoints:

# Fetch Smartsheet public API spec
curl -s https://developers.smartsheet.com/_spec/api/smartsheet/openapi.json > /tmp/openapi.json

# Find the endpoint (example: GET /users/{userId}/plans)
jq '.paths."/users/{userId}/plans".get' /tmp/openapi.json

For unreleased endpoints:

Request OpenAPI spec from PR author
If no spec exists: BLOCK the PR - implementation without spec is not reviewable

If spec is unavailable: STOP. Request spec before continuing review.

Step 2: Create Model Field Validation Checklist

For each model class in the PR, extract all properties from OpenAPI spec and create a validation checklist.

Example: Validating UserPlan model

OpenAPI spec shows:

UserPlan:
  required: [planId, seatType]
  properties:
    planId:
      type: integer
      format: int64
    seatType:
      type: string
      enum: [MEMBER, VIEWER, EDITOR, ADMIN, CONTRIBUTOR]
    seatTypeLastChangedAt:
      type: string
      format: date-time
    provisionalExpirationDate:
      type: string
      format: date-time
    isInternal:
      type: boolean

Validation checklist:

Step 3: Validate ALL Model Fields vs Spec

CRITICAL: Must validate EVERY field, not spot-check.

For each field in checklist:

Field Exists Check

# Verify field exists in model class
grep -n "private Long planId" UserPlan.java
grep -n "private SeatType seatType" UserPlan.java

Type Mapping Check

OpenAPI type → Java type mapping:

OpenAPI Type	Format	Java Type
integer	int32	Integer
integer	int64	Long
string	-	String
string	date-time	ZonedDateTime
string	date	LocalDate
boolean	-	Boolean
number	float	Float
number	double	Double
array	-	List
object	-	Custom class

Required vs Optional Check

Required fields: Documented in Javadoc or ADVANCED.md
Optional fields: Can be null, no validation errors

Nested Objects Check

If property is object type, recursively validate nested model:

Nested model class exists
All nested properties validated against spec
Proper composition via typed fields

Enum Validation

If property is enum:

Enum class exists with correct name
All enum values from spec are present
No extra enum values not in spec
toString() method for serialization

Step 4: Verify Implementation Patterns

Reference: ADVANCED.md → Request Lifecycle, Resource Module Organization sections

Check 1: Uses AbstractResources Template Methods

REQUIRED: Implementation MUST use AbstractResources, not HttpClient directly.

Correct patterns:

// GET single resource
return getResource(path, ResponseClass.class);

// GET collection with pagination
return listResourcesWithWrapper(path, ResponseClass.class, parameters);

// GET with token pagination
return listResourcesWithTokenPagination(path, ResponseClass.class, parameters);

// POST create
return createResource(path, ResponseClass.class, requestObject);

// PUT update
return updateResource(path, ResponseClass.class, requestObject);

// DELETE
return deleteResource(path, ResponseClass.class);

Red flag: Direct HttpClient usage bypasses retry logic, logging, error handling.

Check 2: Query Parameter Handling

Verify optional query parameters:

// ✅ GOOD: Null check before adding
if (lastKey != null) {
    parameters.put("lastKey", lastKey);
}

// ❌ BAD: Always adds (causes empty params)
parameters.put("lastKey", lastKey);

Check 3: Proper Pagination Type

Match spec pagination type:

PagedResult: Offset-based (has pageNumber, totalCount)
TokenPaginatedResult: Cursor-based (has lastKey)
EventResult: Stream-based (has nextStreamPosition)

Verify implementation uses correct listResources* method for pagination type.

Step 5: Verify ALL 6 Mandatory Test Types Exist

Reference: TESTING.md → The 6 Mandatory Test Case Types section

Count tests in test file. Must find exactly 6 (or more).

Required tests:

✅ testXxxGeneratedUrlIsCorrect - URL and query param validation
✅ testXxxAllResponseBodyProperties - Full response with all optional fields
✅ testXxxRequiredResponseBodyProperties - Minimal response (if WireMock mapping exists)
✅ testXxxError400Response - 4xx client error handling
✅ testXxxError500Response - 5xx server error handling
✅ Additional behavioral test - Edge cases, null handling, etc.

If any test is missing: REQUEST CHANGES with specific list of missing tests.

Common Rationalization to Reject

Developer Says	Your Response
"Required/All tests are redundant"	"They test different failure modes: minimal API responses vs full responses. Both required."
"3 tests are good coverage"	"TESTING.md mandates 6 test types. 'Good' ≠ 'complete'. Request missing tests."
"400/500 tests are the same"	"4xx = client errors (not retried), 5xx = server errors (may retry). Different paths."
"Behavioral tests are nice-to-have"	"TESTING.md lists them as test type #6. Mandatory, not optional."

Step 6: Validate Test Quality

Reference: TESTING.md → Strict Assertion Rules section

For EACH test, verify:

Rule 1: Whole-Object Assertions

// ❌ BAD: Spot checking
assertThat(response.getId()).isEqualTo(123);
assertThat(response.getName()).isEqualTo("Test");
// (missing 10 other fields)

// ✅ GOOD: All fields validated
assertThat(response.getId()).isEqualTo(123);
assertThat(response.getName()).isEqualTo("Test");
assertThat(response.getDescription()).isEqualTo("...");
assertThat(response.getCategories()).hasSize(2);
// (all fields explicitly checked)

Rule 2: Query Parameter Validation as Objects

// ❌ BAD: Existence check only
assertThat(receivedQueryParams.containsKey("maxItems")).isTrue();

// ✅ GOOD: Complete object validation
assertThat(receivedQueryParams.get("maxItems").getValues()).isEqualTo(List.of("100"));

Rule 3: Request Body Validation (POST/PUT)

// ✅ Required for create/update endpoints
String requestBody = wiremockRequest.getBodyAsString();
ObjectMapper objectMapper = new ObjectMapper();
String expectedJson = objectMapper.writeValueAsString(EXPECTED_REQUEST_BODY);
assertThat(objectMapper.readTree(requestBody)).isEqualTo(objectMapper.readTree(expectedJson));

If test quality issues found: REQUEST CHANGES with specific fixes needed.

Step 7: Verify WireMock Mappings Exist

Tests reference WireMock stub mappings. Verify they exist:

# Check if mapping file exists in smartsheet-sdk-tests repo
ls smartsheet-sdk-tests/mappings/*list-user-plans*

If mappings missing: REQUEST CHANGES - tests will fail at runtime.

Decision: Approve or Request Changes

ONLY approve if ALL checks pass:

If ANY check fails: REQUEST CHANGES with specific actionable feedback.

If breaking changes detected without disclosure: BLOCK IMMEDIATELY - do not proceed with other checks.

Red Flags - Do NOT Accept These Arguments

Stop and reject when you hear:

Breaking Changes (CRITICAL):

"It's an improvement, not a breaking change" - API improvements can break code. Still breaking.
"API changed, so SDK should match" - SDK changes are independent breaking changes.
"It's technically compatible" - Behavior changes break expectations. Still breaking.
"We deprecated it" - Deprecation ≠ removal. Removal is breaking.
"Better name" / "More intuitive" - Renaming is breaking. No matter how much better.
"Only affects edge cases" - Any code breakage is breaking, regardless of frequency.

Review Quality:

"Senior developer wrote it, trust them" - Experience ≠ infallible. Validate anyway.
"Tests pass, so it's correct" - Tests can pass with wrong fields/types. Spec is truth.
"We need to merge today" - Time pressure doesn't justify incorrect API contracts.
"Field-by-field validation is tedious" - Tedious beats production bugs. Non-negotiable.
"3 tests are good coverage" - TESTING.md requires 6. Not optional.
"I'll add tests/fields later" - Later never comes. Complete now or reject.
"Spot-check key fields is enough" - Partial validation misses bugs. Validate all.

All of these mean: REQUEST CHANGES or BLOCK. Do not compromise.

Common Rationalizations

Excuse	Reality
Breaking Changes
"It's an improvement"	Improvements can be breaking. If API surface changes, it's breaking.
"API changed, SDK should match"	SDK breaking changes are independent. Still requires major version.
"Technically compatible"	Behavior changes break user expectations. Still breaking.
"We deprecated it already"	Deprecation warns. Removal itself is breaking.
"Better name/More intuitive"	Renaming is breaking. No matter how much better.
"Only edge cases affected"	Any code breakage is breaking, regardless of frequency.
"Tests pass"	Tests don't represent all user code. Breaking is breaking.
"We'll document it"	Documentation doesn't make breaking changes non-breaking.
Review Quality
"Senior dev wrote it"	Authority doesn't prevent spec drift. Validate every field.
"Tests pass" (correctness)	Tests can pass with wrong types, missing fields. Spec is source of truth.
"Merge today"	Time pressure doesn't justify shipping broken API contracts.
"Tedious to check 50 fields"	One missed field = production bug. This is non-negotiable.
"3 tests are good"	TESTING.md mandates 6. "Good" ≠ "complete".
"Required/all tests redundant"	Different failure modes. Both catch different bugs.
"400/500 tests the same"	4xx vs 5xx = client vs server errors, different retry behavior.
"Later we'll add X"	Later never comes. Complete now or block.

Common Mistakes

Mistake 0: Not Checking for Breaking Changes (CRITICAL)

Problem: Approving PRs with breaking changes because they "improve" the API or "match the updated API spec."

Fix: Check for breaking changes FIRST, before any other validation. Block if breaking changes not disclosed in PR description.

Mistake 1: Skipping Spec Validation

Problem: Trusting implementation matches spec without verification.

Fix: Fetch OpenAPI spec and validate EVERY field before approving.

Mistake 2: Accepting Partial Test Coverage

Problem: Approving PR with 3 tests because "it's good coverage."

Fix: Count tests. Must have all 6 types. Request specific missing tests.

Mistake 3: Spot-Checking Fields

Problem: Validating only id/name fields, assuming rest are correct.

Fix: Create checklist from spec. Validate ALL fields. No sampling.

Mistake 4: Accepting Pattern Deviations

Problem: Allowing direct HttpClient usage because "it's simpler."

Fix: Enforce AbstractResources pattern usage. No exceptions.

Mistake 5: Missing instanceof Checks

Problem: Not verifying tests have type validation.

Fix: Scan each test for assertThat(response).isInstanceOf(...). Request if missing.

Mistake 6: Trusting "Tests Pass"

Problem: Assuming passing tests mean correct implementation.

Fix: Passing tests ≠ correct API contract. Spec validation is mandatory.

Mistake 7: Approving "Improvement" Breaking Changes

Problem: Accepting breaking changes because they make the API "better" or "more consistent."

Fix: Quality of change doesn't matter. If it breaks compatibility, it's breaking. Must be disclosed.

Real-World Impact

Without rigorous review (especially breaking changes detection):

Users' code breaks on SDK upgrades (CRITICAL)
Users stuck on old SDK versions unable to upgrade
Trust damage from surprise breaking changes
Production bugs from mismatched field types
Silent failures when optional fields missing
API contract violations shipped to customers
Incomplete test coverage gives false confidence
Technical debt from pattern deviations
Difficult debugging from inconsistent error handling

With this review process:

Breaking changes caught before shipping (CRITICAL)
Semantic versioning enforced - users trust version numbers
Migration paths provided - users can upgrade confidently
API contracts match specifications exactly
Complete test coverage prevents regressions
Consistent architecture enables maintainability
Spec validation catches bugs before production
Quality bar maintained across all endpoints