[Schema] Always emit {} for empty tool schema properties - #407
Merged
chr-hertel merged 2 commits intoAug 14, 2026
Merged
Conversation
BrocksiNet
requested review from
CodeWithKyrian,
Nyholm,
chr-hertel and
soyuka
as code owners
July 28, 2026 11:44
chr-hertel
previously approved these changes
Aug 14, 2026
chr-hertel
left a comment
chr-hertel
left a comment
Member
There was a problem hiding this comment.
Thanks @BrocksiNet - will extend the list of supported keywords and rebase for v0.8.0 while merging. Thanks for the patch!
chr-hertel
added
Schema
Normalize empty properties arrays (including nested object schemas and outputSchema) in Tool::__construct so tools/list never serializes invalid JSON Schema properties: []. Fixes modelcontextprotocol#405
Walking into `items` and `additionalProperties` without normalizing an empty
sub-schema at those positions left the `[]`-instead-of-`{}` bug intact one
level down. Most notably it regressed modelcontextprotocol#151 on a `Tool::fromArray()`
round-trip: `SchemaGenerator` emits `items: {}` for untyped array parameters,
which decodes to `[]` and was re-serialized as `[]` — the exact schema strict
clients reject.
Empty sub-schemas are now replaced with a `\stdClass` at every schema
position, and the keyword list is completed to cover draft-07 through
2020-12: `$defs`, `definitions`, `dependentSchemas`, `patternProperties`,
`propertyNames`, `contains`, `not`, `if`/`then`/`else`, `additionalItems`,
and `unevaluatedItems`/`unevaluatedProperties`. Keywords holding plain JSON
arrays (`allOf: []`, `enum: []`, `dependentRequired`) keep encoding as `[]`.
chr-hertel
force-pushed
the
fix/405-normalize-empty-tool-schema-properties
branch
from
August 14, 2026 19:46
3211fa1 to
05ac007
Compare
chr-hertel
approved these changes
Aug 14, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
propertiesnormalization intoTool::__construct()so every construction path (not onlyfromArray/SchemaGenerator) emits JSON Schema objects as{}instead of[].items,additionalProperties, and combinators, and apply it tooutputSchemaas well.json_decoderound-trips, nested objects, array item schemas, and emptyoutputSchema.properties.Fixes #405
Test plan
make unit-tests(834 tests)make phpstanmake csmake inspector-tests(95 tests, 7 skipped)composer validate --strict"properties":{}intools/listagainst a strict client (e.g. OpenAI-compatible)