rule-parity.md

description	Which breaking-change rules actually fire for OpenAPI, Swagger 2.0, AsyncAPI, GraphQL, gRPC, MCP and WSDL -- measured by making every rule fire, not asserted.

Rule parity across protocols

Which of the breaking-change rules actually fire, for each format this tool reads.

This table is derived, not asserted. Each protocol's shipped contract is loaded into the normalized model, perturbed in each of the ways listed below, and diffed against itself; the cells record what the rules said. A matrix claiming coverage nobody demonstrated is worse than no matrix, because it is the kind of thing that gets quoted in an evaluation.

How to read an empty cell

It means no mutation here produced that rule for that protocol. It does not mean the rule cannot fire. The mutation list is finite and deliberately small — changes a person would actually make — so an empty cell is a fact about this harness, not a limit of the engine.

The useful signal is the shape: a rule that fires for one protocol and not another usually means the second format cannot express the change, or its parser does not carry the field the rule reads. BRK-FIELD-NUMBER-* firing only for gRPC is the model working correctly; a schema rule firing only for OpenAPI would be a parser that is not populating something.

What was changed

Mutation	Stands for
remove an operation	an endpoint or RPC is deleted
deprecate an operation	an endpoint is marked deprecated
remove a response field	a field consumers read is gone
add a required request field	callers must now send something new
remove a request field	an accepted input disappears
change a response field's type	consumers parse the wrong thing
narrow an enum	a previously valid value is refused
tighten a constraint	previously valid input fails
make an optional request field required	an omission that used to be fine is not
remove a parameter	a query or path input is gone
add a required parameter	callers must send more
remove a response status	a declared outcome is gone
remove a response header	a promised header is gone
change security	what a caller must present changes
reuse a field number	stored protobuf data misdecodes
remove a reservation	a retired number can be reused
change streaming	generated clients call the RPC wrongly
widen an enum	a new value starts being accepted
narrow a response enum	a value consumers switched on stops being returned
loosen a constraint	a declared bound is dropped
add a response field	the response grows
guarantee a response field	an optional response field starts always being sent
make a response field optional	a guarantee is withdrawn
add an operation	a new endpoint or RPC
un-deprecate an operation	a retirement is called off
add an optional parameter	a new opt-in input
make a parameter optional	an input stops being needed
make a parameter required	an input starts being needed
change a parameter's type	callers send the wrong shape
add a response header	a new promised header
add a response status	a new declared outcome
change a media type	the wire format moves
remove the request body	an endpoint stops taking one
require the request body	it stops being optional
lose field presence	unset and default become the same
move a field into a oneof	fields become exclusive
un-reserve a field number	a retired protobuf number can be handed out again
change a dependent requirement	sending one field starts requiring another
change a tuple	positional items shift
change contains	an array's membership rule moves
change pattern properties	a whole family of fields changes at once
change property names	which keys are allowed moves
change a conditional	an if/then branch applies elsewhere
set an MCP annotation	a tool claims something new
clear an MCP annotation	a tool stops claiming it
change a tool description	the routing input an agent reads is edited
add an output schema	a tool starts guaranteeing a shape
remove an output schema	it stops guaranteeing one
add an optional request field	a new input callers may send
make a request field optional	an input stops being mandatory
add a required request body	an endpoint that took nothing now needs a body
change the SOAPAction	the header a gateway routes on, with every schema untouched
change the binding style	document becomes rpc
change the SOAP version	1.1 becomes 1.2
bump the version	a release, with nothing else changed

Rules

Rule	Severity	asyncapi	grpc	mcp	openapi	openapi (2020-12)	swagger2	wsdl
BRK-CONDITIONAL-SCHEMA-CHANGED	WARN
BRK-CONSTRAINT-LOOSENED	INFO
BRK-CONSTRAINT-TIGHTENED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-CONTAINS-CHANGED	WARN					✓
BRK-DEPENDENT-REQUIRED-ADDED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-DEPENDENT-REQUIRED-REMOVED	WARN
BRK-DEPENDENT-SCHEMA-CHANGED	WARN
BRK-DEPRECATION-ADDED	WARN	✓	✓	✓	✓	✓	✓	✓
BRK-DEPRECATION-REMOVED	INFO
BRK-ENUM-NARROWED-REQUEST	ERROR	✓		✓	✓	✓	✓
BRK-ENUM-NARROWED-RESPONSE	WARN
BRK-ENUM-WIDENED	INFO	✓		✓	✓	✓	✓
BRK-FIELD-NUMBER-REUSED	ERROR		✓
BRK-FIELD-NUMBER-UNRESERVED	WARN		✓
BRK-FIELD-PRESENCE-LOST	ERROR		✓
BRK-HEADER-ADDED	INFO		✓	✓	✓	✓	✓	✓
BRK-HEADER-REMOVED	WARN
BRK-MCP-ANNOTATION-DECLARATION-CHANGED	INFO
BRK-MCP-DESTRUCTIVE-HINT-CLEARED	WARN
BRK-MCP-DESTRUCTIVE-HINT-SET	WARN			✓
BRK-MCP-IDEMPOTENT-HINT-CLEARED	WARN
BRK-MCP-IDEMPOTENT-HINT-SET	WARN
BRK-MCP-MANIFEST-TRUNCATED	ERROR
BRK-MCP-OPENWORLD-HINT-CHANGED	INFO
BRK-MCP-OUTPUT-SCHEMA-ADDED	WARN			✓
BRK-MCP-OUTPUT-SCHEMA-REMOVED	ERROR			✓
BRK-MCP-READONLY-HINT-CLEARED	WARN			✓
BRK-MCP-READONLY-HINT-SET	WARN
BRK-MCP-TOOL-DESCRIPTION-CHANGED	WARN			✓
BRK-MCP-TOOL-RENAME-SUSPECTED	INFO
BRK-MEDIA-TYPE-CHANGED	ERROR				✓		✓
BRK-ONEOF-NARROWED	ERROR
BRK-ONEOF-WIDENED	INFO
BRK-OP-ADDED	INFO				✓	✓	✓
BRK-OP-REMOVED	ERROR				✓	✓	✓
BRK-PARAM-ADDED-OPTIONAL	INFO	✓	✓	✓	✓	✓	✓	✓
BRK-PARAM-ADDED-REQUIRED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-PARAM-OPTIONALIZED	INFO				✓		✓
BRK-PARAM-REMOVED	ERROR				✓		✓
BRK-PARAM-REQUIRED	ERROR				✓		✓
BRK-PARAM-TYPE-CHANGED	ERROR				✓		✓
BRK-PATTERN-PROPERTIES-CHANGED	WARN
BRK-PROPERTY-NAMES-CHANGED	WARN
BRK-REQ-BODY-ADDED-OPTIONAL	INFO	✓	✓	✓	✓	✓	✓	✓
BRK-REQ-BODY-ADDED-REQUIRED	ERROR
BRK-REQ-BODY-REMOVED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-REQ-BODY-REQUIRED	ERROR				✓
BRK-REQ-FIELD-ADDED-OPTIONAL	INFO	✓	✓	✓	✓	✓	✓	✓
BRK-REQ-FIELD-ADDED-REQUIRED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-REQ-FIELD-BECAME-REQUIRED	ERROR	✓	✓	✓	✓	✓	✓
BRK-REQ-FIELD-OPTIONALIZED	INFO	✓		✓	✓	✓	✓	✓
BRK-REQ-FIELD-REMOVED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-REQ-NULLABLE-ADDED	INFO
BRK-REQ-NULLABLE-REMOVED	ERROR
BRK-RESERVATION-REMOVED	WARN		✓
BRK-RESP-CONSTRAINT-LOOSENED	WARN
BRK-RESP-CONSTRAINT-TIGHTENED	WARN					✓
BRK-RESP-FIELD-ADDED	INFO		✓	✓	✓	✓	✓	✓
BRK-RESP-FIELD-GUARANTEED	INFO		✓	✓		✓
BRK-RESP-FIELD-OPTIONALIZED	ERROR			✓		✓		✓
BRK-RESP-FIELD-REMOVED	ERROR		✓	✓		✓		✓
BRK-RESP-NULLABLE-ADDED	WARN
BRK-RESP-NULLABLE-REMOVED	INFO
BRK-RESP-STATUS-ADDED	INFO		✓	✓	✓	✓	✓	✓
BRK-RESP-STATUS-REMOVED	ERROR						✓	✓
BRK-RESP-TYPE-CHANGED	WARN		✓	✓		✓		✓
BRK-RPC-ADDED	INFO		✓	✓				✓
BRK-RPC-REMOVED	ERROR	✓	✓	✓				✓
BRK-RPC-STREAMING-CHANGED	ERROR		✓
BRK-SECURITY-CHANGED	ERROR	✓	✓	✓	✓	✓	✓	✓
BRK-SOAP-ACTION-CHANGED	ERROR							✓
BRK-SOAP-STYLE-CHANGED	ERROR							✓
BRK-SOAP-VERSION-CHANGED	ERROR							✓
BRK-STREAM-ENCODING-CHANGED	ERROR
BRK-STREAM-ITEM-SCHEMA-ADDED	INFO
BRK-STREAM-ITEM-SCHEMA-REMOVED	ERROR
BRK-STREAM-PREFIX-COUNT-CHANGED	ERROR
BRK-STREAM-SEQUENTIAL-CHANGED	ERROR
BRK-TUPLE-SHAPE-CHANGED	ERROR					✓

Rules no mutation produced

The interesting column. Each of these is either a mutation this harness does not make, or a rule no input can produce — and the second is a defect this project has found four separate times. Listed rather than hidden in a table of empty cells.

• BRK-CONDITIONAL-SCHEMA-CHANGED — An if/then/else branch was added, removed or changed. What is valid now depends on a condition, and the condition moved.
• BRK-CONSTRAINT-LOOSENED — A request constraint was loosened (previously invalid inputs pass).
• BRK-DEPENDENT-REQUIRED-REMOVED — A field no longer forces another to be present. Harmless in a request; in a response it withdraws a guarantee consumers may read unconditionally.
• BRK-DEPENDENT-SCHEMA-CHANGED — A schema that applies only when some field is present was added, removed or changed; what is valid now depends on which fields are sent.
• BRK-DEPRECATION-REMOVED — The deprecation marker was removed.
• BRK-ENUM-NARROWED-RESPONSE — Response enum values were removed; clients may encounter undeclared values at runtime.
• BRK-HEADER-REMOVED — A declared response header was removed.
• BRK-MCP-ANNOTATION-DECLARATION-CHANGED — An annotation moved between false and undeclared without changing what it asserts.
• BRK-MCP-DESTRUCTIVE-HINT-CLEARED — A tool stopped declaring destructiveHint; hosts may stop gating behaviour that nobody re-verified as safe.
• BRK-MCP-IDEMPOTENT-HINT-CLEARED — A tool stopped claiming idempotentHint; a retry that was safe may now duplicate its effect.
• BRK-MCP-IDEMPOTENT-HINT-SET — A tool now claims idempotentHint; hosts may begin retrying a call that was not previously retry-safe.
• BRK-MCP-MANIFEST-TRUNCATED — One side is a single page of a paginated tools/list. Every tool past the page boundary reads as removed, so the whole comparison is unsound.
• BRK-MCP-OPENWORLD-HINT-CHANGED — openWorldHint changed. It describes the domain a tool reaches into and constrains no caller.
• BRK-MCP-READONLY-HINT-SET — A tool now claims readOnlyHint; hosts may stop asking for confirmation on a claim nobody verified.
• BRK-MCP-TOOL-RENAME-SUSPECTED — Exactly one tool disappeared and one appeared with an identical schema. Context for the removal, which is still reported: a manifest carries no identity but the name, so a rename cannot be distinguished from remove-plus-add.
• BRK-ONEOF-NARROWED — A protobuf field moved into a oneof; it is now exclusive with the others.
• BRK-ONEOF-WIDENED — A protobuf field moved out of a oneof; no existing sender can notice.
• BRK-PATTERN-PROPERTIES-CHANGED — The schema applied to properties matching a name pattern was added, removed or changed; a whole family of fields changed shape at once.
• BRK-PROPERTY-NAMES-CHANGED — The constraint on what property names are allowed changed; keys that used to be accepted may not be.
• BRK-REQ-BODY-ADDED-REQUIRED — A required request body was added.
• BRK-REQ-NULLABLE-ADDED — A request field now accepts null as well (additive).
• BRK-REQ-NULLABLE-REMOVED — A request field that accepted null no longer does; payloads that were valid are now rejected.
• BRK-RESP-CONSTRAINT-LOOSENED — A bound on a response field was relaxed or removed; the service may now return values a consumer written against the old bound rejects.
• BRK-RESP-NULLABLE-ADDED — A response value that was never null may now be null; every reader that did not check breaks on the first one, and in a generated client the field changes type at every use site.
• BRK-RESP-NULLABLE-REMOVED — A response value can no longer be null (narrowing a response is safe for readers).
• BRK-STREAM-ENCODING-CHANGED — The encoding of a streamed item changed; the part still arrives and the parser reading it fails.
• BRK-STREAM-ITEM-SCHEMA-ADDED — A sequential media type now declares itemSchema.
• BRK-STREAM-ITEM-SCHEMA-REMOVED — A sequential media type stopped declaring itemSchema, so nothing describes one item any more.
• BRK-STREAM-PREFIX-COUNT-CHANGED — The number of leading parts in a multipart stream changed; prefixEncoding is positional, so a reader counting parts reads the wrong one from there on.
• BRK-STREAM-SEQUENTIAL-CHANGED — A payload moved between a single document and a sequence of items; every client has to be rewritten even when the item shape is identical.

49 of 79 rules observed firing across 7 protocol(s) and 55 mutations.