fix(tools): normalize truly empty MCP tool schemas for OpenAI by Bartok9 · Pull Request #60176 · openclaw/openclaw

Bartok9 · 2026-04-03T08:43:46Z

Summary

MCP tools with parameter-free schemas may return truly empty objects {} without a type field. The existing normalization handled { type: "object" } → { type: "object", properties: {} } but missed the truly empty case.

Problem

OpenAI gpt-5.4 rejects tool schemas without type: "object" and properties, causing HTTP 400 errors:

Invalid schema for function 'flux-mcp__get_flux_instance':
In context=(), object schema missing properties.

This was happening for MCP tools like flux-operator-mcp that expose parameter-free tool schemas.

Root Cause

The normalizeToolParameterSchema function in pi-tools.schema.ts handled three cases:

Schemas with both type and properties → pass through
Schemas with no type but with properties or required → add type: "object"
Schemas with type but no properties → add properties: {}

But it did not handle truly empty schemas {} that have neither type nor properties. These fell through to the final return schema without normalization.

Fix

Added a condition before the final pass-through to catch empty schemas (no type, no properties, no unions) and normalize them to { type: "object", properties: {} }.

Testing

Added test case: "normalizes truly empty schemas to type:object with properties:{} (MCP parameter-free tools)"
All existing tests pass

greptile-apps · 2026-04-03T08:45:08Z

Greptile Summary

Adds a missing normalization branch in normalizeToolParameterSchema for MCP tool schemas that are truly empty {} — having neither a type field nor properties. These schemas now get normalized to { type: "object", properties: {} } before being sent to OpenAI, matching the existing treatment of { type: "object" } schemas and resolving the HTTP 400 errors. A focused test case is added alongside the existing ones.

Confidence Score: 5/5

Safe to merge — the fix is minimal, correctly guarded, and covered by a new test.

The new condition fires only after confirming neither type nor properties is present (and after all existing early-return branches have already been checked), so it cannot interfere with schemas already handled. The spread order { type: "object", properties: {}, ...schemaRecord } is safe because the guard ensures those keys are absent in schemaRecord. No P0/P1 findings.

No files require special attention.

_{Reviews (1): Last reviewed commit: "fix(tools): normalize truly empty MCP to..." | Re-trigger Greptile}

Fixes openclaw#60158 MCP tools with parameter-free schemas may return truly empty objects `{}` without a `type` field. The existing normalization handled `{ type: "object" }` → `{ type: "object", properties: {} }` but missed the truly empty case. OpenAI gpt-5.4 rejects tool schemas without `type: "object"` and `properties`, causing HTTP 400 errors: ``` Invalid schema for function 'flux-mcp__get_flux_instance': In context=(), object schema missing properties. ``` This change catches empty schemas (no type, no properties, no unions) before the final pass-through and converts them to the required format. Added test case for parameter-free MCP tool schemas.

@Bartok9

…nks @Bartok9)

steipete · 2026-04-03T11:45:49Z

Landed via temp rebase onto main.

Gate: pnpm check && pnpm test && pnpm build
Land commit: 90633d8
Merge commit: 57999f9

Thanks @Bartok9!

@Bartok9

…nks @Bartok9)

prtags · 2026-04-23T18:49:35Z

Related work from PRtags group unique-heron-2zsc

Title: Open PR duplicate: MCP schema properties + auto-reset override self-heal composite

Number	Title
#58299	fix: normalize MCP tool schemas missing properties field for OpenAI Responses API
#60176*	fix(tools): normalize truly empty MCP tool schemas for OpenAI
#69419	session: clear auto-sourced model/auth overrides on /new and /reset
#69956	fix(mcp-http): ensure MCP tool schemas always include properties field

* This PR

Bartok9 · 2026-04-23T21:39:12Z

Thank you @steipete for landing it! Glad the fix was clean — the truly-empty {} case is one of those easy-to-miss edge cases that only shows up with certain MCP tool definitions. 🎻

@Bartok9

…nks @Bartok9)

…o OpenAI (openclaw#75362) MCP servers may return inputSchema as { type: "object" } without a properties field, or with properties set to undefined/null. The hasTopLevelObjectSchema guard only checked 'properties' in schemaRecord (key existence) without verifying the value is a real object. This caused such schemas to pass through unnormalized, resulting in OpenAI rejecting them with 'object schema missing properties'. Fix: tighten hasTopLevelObjectSchema to require properties to be a non-null object, and broaden isTypedSchemaMissingProperties to catch properties keys with undefined/null values. Regression of openclaw#60158 (originally fixed by openclaw#60176).

…o OpenAI (#75362) MCP servers may return inputSchema as { type: "object" } without a properties field, or with properties set to undefined/null. The hasTopLevelObjectSchema guard only checked 'properties' in schemaRecord (key existence) without verifying the value is a real object. This caused such schemas to pass through unnormalized, resulting in OpenAI rejecting them with 'object schema missing properties'. Fix: tighten hasTopLevelObjectSchema to require properties to be a non-null object, and broaden isTypedSchemaMissingProperties to catch properties keys with undefined/null values. Regression of #60158 (originally fixed by #60176).

@Bartok9

…nks @Bartok9)

…o OpenAI (openclaw#75362) MCP servers may return inputSchema as { type: "object" } without a properties field, or with properties set to undefined/null. The hasTopLevelObjectSchema guard only checked 'properties' in schemaRecord (key existence) without verifying the value is a real object. This caused such schemas to pass through unnormalized, resulting in OpenAI rejecting them with 'object schema missing properties'. Fix: tighten hasTopLevelObjectSchema to require properties to be a non-null object, and broaden isTypedSchemaMissingProperties to catch properties keys with undefined/null values. Regression of openclaw#60158 (originally fixed by openclaw#60176).

@Bartok9

…nks @Bartok9)

…o OpenAI (openclaw#75362) MCP servers may return inputSchema as { type: "object" } without a properties field, or with properties set to undefined/null. The hasTopLevelObjectSchema guard only checked 'properties' in schemaRecord (key existence) without verifying the value is a real object. This caused such schemas to pass through unnormalized, resulting in OpenAI rejecting them with 'object schema missing properties'. Fix: tighten hasTopLevelObjectSchema to require properties to be a non-null object, and broaden isTypedSchemaMissingProperties to catch properties keys with undefined/null values. Regression of openclaw#60158 (originally fixed by openclaw#60176).

@Bartok9

…nks @Bartok9)

…o OpenAI (openclaw#75362) MCP servers may return inputSchema as { type: "object" } without a properties field, or with properties set to undefined/null. The hasTopLevelObjectSchema guard only checked 'properties' in schemaRecord (key existence) without verifying the value is a real object. This caused such schemas to pass through unnormalized, resulting in OpenAI rejecting them with 'object schema missing properties'. Fix: tighten hasTopLevelObjectSchema to require properties to be a non-null object, and broaden isTypedSchemaMissingProperties to catch properties keys with undefined/null values. Regression of openclaw#60158 (originally fixed by openclaw#60176).

@Bartok9

…nks @Bartok9)

openclaw-barnacle Bot added agents Agent runtime and tooling size: XS labels Apr 3, 2026

Bartok Moltbot and others added 2 commits April 3, 2026 20:17

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

90633d8

…nks @Bartok9)

steipete force-pushed the fix/60158-empty-mcp-tool-schema branch from 751773a to 90633d8 Compare April 3, 2026 11:45

steipete merged commit 57999f9 into openclaw:main Apr 3, 2026
9 checks passed

steipete added a commit to duncanita/openclaw that referenced this pull request Apr 4, 2026

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

b62fc0f

…nks @Bartok9)

prtags Bot mentioned this pull request Apr 23, 2026

fix: normalize MCP tool schemas missing properties field for OpenAI Responses API #58299

Merged

This was referenced Apr 23, 2026

session: clear auto-sourced model/auth overrides on /new and /reset #69419

Merged

fix(mcp-http): ensure MCP tool schemas always include properties field #69956

Closed

lovewanwan pushed a commit to lovewanwan/openclaw that referenced this pull request Apr 28, 2026

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

bfde49e

…nks @Bartok9)

tolkonepiu mentioned this pull request May 1, 2026

[Bug]: Regression: openai/gpt-5.4 rejects parameter-free MCP tool schemas again in v2026.4.27 #75362

Closed

SymbolStar mentioned this pull request May 1, 2026

fix(mcp): normalize empty parameter-free tool schema before sending to OpenAI (#75362) #75401

Merged

clawsweeper Bot mentioned this pull request May 1, 2026

fix: normalize null params to {} for empty object schemas (prevents infinite loops) #72634

Closed

clawsweeper Bot mentioned this pull request May 2, 2026

fix(mcp): normalize empty parameter-free tool schema before sending to OpenAI (#75362) #75941

Closed

ogt-redknie pushed a commit to ogt-redknie/OPENX that referenced this pull request May 2, 2026

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

3632441

…nks @Bartok9)

tolkonepiu mentioned this pull request May 4, 2026

[Bug]: Parameter-free MCP tool schema regression still reproducible in v2026.5.2 #77043

Closed

SymbolStar mentioned this pull request May 4, 2026

fix(mcp): normalize parameter-free tool inputSchema for OpenAI (#77043) #77230

Closed

github-actions Bot pushed a commit to Desicool/openclaw that referenced this pull request May 9, 2026

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

5578c4e

…nks @Bartok9)

github-actions Bot pushed a commit to Desicool/openclaw that referenced this pull request May 24, 2026

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

a3c7833

…nks @Bartok9)

Nachx639 pushed a commit to Nachx639/clawdbot that referenced this pull request Jun 17, 2026

fix: narrow empty MCP tool schema normalization (openclaw#60176) (tha…

7f4bb2d

…nks @Bartok9)

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fix(tools): normalize truly empty MCP tool schemas for OpenAI#60176

fix(tools): normalize truly empty MCP tool schemas for OpenAI#60176
steipete merged 2 commits into
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Bartok9:fix/60158-empty-mcp-tool-schema

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Bartok9 commented Apr 3, 2026

Summary

Problem

Root Cause

Fix

Testing

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greptile-apps Bot commented Apr 3, 2026

Greptile Summary

Confidence Score: 5/5

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