Stop checking MCP tool schemas for type definitions by geoffdowns · Pull Request #9574 · google-gemini/gemini-cli

geoffdowns · 2025-09-25T06:39:16Z

TLDR

This change removes the hasValidTypes method added in #5694 as the check is overly restrictive and prevents the use of valid MCP tools.

Dive Deeper

The hasValidTypes method attempted to enforce that MCP tools provide a JSON schema that would be accepted by the Gemini/Vertex AI APIs (after first being converted into a FunctionDeclaration by the GenAI SDK). The restriction was added in response to #4594 and (related): awslabs/mcp#661

However, the JSON schema generated by the MCP server referenced in those issues is a valid JSON schema and has types defined for all the schema elements. The MCP inputSchema is:

"inputSchema":{
  "$defs":{
    "DiagramType":{
      "description":"Enum for supported diagram types.",
      "enum":["aws","sequence","flow","class","k8s","onprem","custom","all"],
      "title":"DiagramType",
      "type":"string"
    }
  },
  "properties":{
    "diagram_type":{
      "$ref":"#/$defs/DiagramType",
      "default":"all",
      "description":"Type of diagram example to return. Options: aws, sequence, flow, class, k8s, onprem, custom, all"
    }
  },
  "title":"mcp_get_diagram_examplesArguments",
  "type":"object"
}}

This JSON schema uses JSON pointer references. The hasValidTypes method incorrectly rejects MCP tools that use this JSON schema feature.

The original error was caused by lossy conversion of the MCP input schema in the GenAI SDK. The information loss was remediated by setting the functionDeclaration.parametersJsonSchema instead of converting to the genai-js types.Schema object and setting the functionDeclaration.parameters field. This change was made in: googleapis/js-genai@36f6350#diff-fdde9372aec859322b7c5a5efe467e0ad25a57210c7229724586ee90ea4f5a30

The original intent of #5694 was to prevent one bad MCP tool schema from causing all Gemini API calls to fail. The underlying issue was never with the MCP tool schemas, however, and the Gemini API accepts JSON schemas that use $ref/$def or even omit type information altogether.

Reviewer Test Plan

Use GCLI with any MCP tool that uses the $refs JSON schema feature. The tool should no longer be filtered out during initialization. Gemini API calls should succeed and the tool should work as expected.

Testing Matrix

	🍏	🪟	🐧
npm run	x	❓	❓
npx	❓	❓	❓
Docker	❓	❓	❓
Podman	❓	-	-
Seatbelt	❓	-	-

Linked issues / bugs

Fixes #6219

gemini-code-assist · 2025-09-25T06:39:32Z

Summary of Changes

Hello @geoffdowns, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refines the handling of Model Context Protocol (MCP) tools by eliminating an overly stringent schema validation check. The hasValidTypes method, originally implemented to ensure compatibility with Gemini/Vertex AI APIs, was inadvertently rejecting valid MCP tool schemas that employed JSON pointer references. Its removal ensures that all correctly defined MCP tools can be seamlessly integrated and utilized, thereby resolving a prior issue where such tools were being filtered out.

Highlights

Removal of hasValidTypes function: The hasValidTypes method, which was previously added to validate MCP tool schemas, has been entirely removed. This function was found to be overly restrictive and incorrectly rejected valid tool schemas.
Improved MCP Tool Compatibility: MCP tools that utilize advanced JSON schema features, such as JSON pointer references ($ref and $defs), are now correctly processed and no longer filtered out. This resolves issues where valid tools were being prevented from use.
Resolution of Issue version >= 0.1.18 rejects MCP functions with ambiguous type info #6219: This change directly addresses and fixes issue version >= 0.1.18 rejects MCP functions with ambiguous type info #6219, which reported problems with MCP tools being incorrectly rejected due to the restrictive schema validation.

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Code Review

This pull request correctly removes the hasValidTypes validation for MCP tool schemas, which was overly restrictive. The function and its direct tests have been removed. However, a related test case that verifies the skipping of tools with invalid schemas was missed and will now fail. This needs to be removed to complete the change.

geoffdowns · 2025-09-25T06:55:49Z

Code Review

This pull request correctly removes the hasValidTypes validation for MCP tool schemas, which was overly restrictive. The function and its direct tests have been removed. However, a related test case that verifies the skipping of tools with invalid schemas was missed and will now fail. This needs to be removed to complete the change.

fixed

…options (google-gemini#9540) Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com>

…ni#9517) Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

…splaying to user (google-gemini#8636)

…e-gemini#9769)

Co-authored-by: Shreya Keshive <skeshive@gmail.com>

…gemini#9253)

…9785)

google-gemini#9786)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Co-authored-by: Gal Zahavi <38544478+galz10@users.noreply.github.com> Co-authored-by: anthony bushong <agmsb@users.noreply.github.com> Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com> Co-authored-by: Sandy Tao <sandytao520@icloud.com> Co-authored-by: Jacob MacDonald <jakemac@google.com> Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com> Co-authored-by: christine betts <chrstn@uw.edu> Co-authored-by: Adam Weidman <65992621+adamfweidman@users.noreply.github.com> Co-authored-by: matt korwel <matt.korwel@gmail.com> Co-authored-by: Shreya Keshive <skeshive@gmail.com> Co-authored-by: HugoMurillo <mhugorodrigo@google.com> Co-authored-by: Shreya Keshive <shreyakeshive@google.com> Co-authored-by: Miguel Solorio <miguelsolorio@google.com> Co-authored-by: Christie Warwick (Wilson) <bobcatfish@gmail.com> Co-authored-by: shrutip90 <shruti.p90@gmail.com>

…itions (google-gemini#9574)

…-proprietary#4774) In the past, Gemini CLI doesn't work with the Semgrep MCP server when we use our custom types. [Other MCP servers are also running into this error.](google-gemini/gemini-cli#6219) Gemini recently [released a fix ](google-gemini/gemini-cli#9574 this, so we should add the types back so models like GPT-5 can call our tools properly. Fixes SAF-2262 ## Test plan: ``` ███ █████████ ██████████ ██████ ██████ █████ ██████ █████ █████ ░░░███ ███░░░░░███░░███░░░░░█░░██████ ██████ ░░███ ░░██████ ░░███ ░░███ ░░░███ ███ ░░░ ░███ █ ░ ░███░█████░███ ░███ ░███░███ ░███ ░███ ░░░███ ░███ ░██████ ░███░░███ ░███ ░███ ░███░░███░███ ░███ ███░ ░███ █████ ░███░░█ ░███ ░░░ ░███ ░███ ░███ ░░██████ ░███ ███░ ░░███ ░░███ ░███ ░ █ ░███ ░███ ░███ ░███ ░░█████ ░███ ███░ ░░█████████ ██████████ █████ █████ █████ █████ ░░█████ █████ ░░░ ░░░░░░░░░ ░░░░░░░░░░ ░░░░░ ░░░░░ ░░░░░ ░░░░░ ░░░░░ ░░░░░ v0.9.0-nightly.20251001.163dba7e Tips for getting started: 1. Ask questions, edit files, or run commands. 2. Be specific for the best results. 3. Create GEMINI.md files to customize your interactions with Gemini. 4. /help for more information. > /mcp Configured MCP servers: 🟢 serverName - Ready (7 tools, 2 prompts) Tools: - get_abstract_syntax_tree - get_supported_languages - semgrep_findings - semgrep_rule_schema - semgrep_scan - semgrep_scan_supply_chain - semgrep_scan_with_custom_rule Prompts: - setup_semgrep_mcp - write_custom_semgrep_rule 💡 Tips: - Use /mcp desc to show server and tool descriptions - Use /mcp schema to show tool parameter schemas - Use /mcp nodesc to hide descriptions - Use /mcp auth <server-name> to authenticate with OAuth-enabled servers - Press Ctrl+T to toggle tool descriptions on/off Using: 1 MCP server (ctrl+t to view) ╭──────────────────────────────────────────────────────────────────────────────────╮ │ > Type your message or @path/to/file │ ╰──────────────────────────────────────────────────────────────────────────────────╯ ~/Desktop/semgrep-proprietary no sandbox (see gemini-2.5-pro (100% (katrina/mcp-types*) /docs) context left) ``` Also tested that Cursor was able to call `semgrep_scan` after the change with the GPT-5 model (and that it was not able to call the tool nicely before the change) ![image.png](https://app.graphite.dev/user-attachments/assets/dd7a3921-5c61-4f48-b262-12b893a037e7.png) synced from Pro 6ee3493829fff70665a892703aef809bf8899094

Co-authored-by: Gal Zahavi <38544478+galz10@users.noreply.github.com> Co-authored-by: anthony bushong <agmsb@users.noreply.github.com> Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com> Co-authored-by: Sandy Tao <sandytao520@icloud.com> Co-authored-by: Jacob MacDonald <jakemac@google.com> Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com> Co-authored-by: christine betts <chrstn@uw.edu> Co-authored-by: Adam Weidman <65992621+adamfweidman@users.noreply.github.com> Co-authored-by: matt korwel <matt.korwel@gmail.com> Co-authored-by: Shreya Keshive <skeshive@gmail.com> Co-authored-by: HugoMurillo <mhugorodrigo@google.com> Co-authored-by: Shreya Keshive <shreyakeshive@google.com> Co-authored-by: Miguel Solorio <miguelsolorio@google.com> Co-authored-by: Christie Warwick (Wilson) <bobcatfish@gmail.com> Co-authored-by: shrutip90 <shruti.p90@gmail.com>

remove hasValidTypes method

7258bc7

geoffdowns requested a review from a team as a code owner September 25, 2025 06:39

gemini-code-assist Bot reviewed Sep 25, 2025

View reviewed changes

fix additional unit test

bb892ec

galz10 approved these changes Sep 25, 2025

View reviewed changes

Merge branch 'main' into remove-type-checks

21fe45d

bbiggs added this pull request to the merge queue Sep 25, 2025

github-merge-queue Bot removed this pull request from the merge queue due to failed status checks Sep 25, 2025

bbiggs added this pull request to the merge queue Sep 25, 2025

github-merge-queue Bot removed this pull request from the merge queue due to failed status checks Sep 25, 2025

galz10 added the maintainer:e2e:ok label Sep 25, 2025

geoffdowns and others added 17 commits September 25, 2025 17:24

fix integration test

bb1356e

fix(core): ensure retry sets defaults for nullish values passed into …

37a09de

…options (google-gemini#9540) Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com>

fix(core): Improve API error retry logic (google-gemini#9763)

103f6e5

Re-request consent if necessary when updating extensions (google-gemi…

33b5760

…ni#9517) Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Fix duplicate info messages for extension updates (google-gemini#9760)

2ac75b6

Throw error for invalid extension names (google-gemini#9538)

94f95b7

feat(escape ansi): escape ansi ctrl codes from model output before di…

4430b72

…splaying to user (google-gemini#8636)

fix(ci): e2e workflow aligned with release (google-gemini#9296)

53914e0

fix(ui): Truncate long loading text (google-gemini#9768)

81b1cc9

fix(zed): Fix broken 'auto' model selection in Zed integration (googl…

ab6f21d

…e-gemini#9769)

test: disable all IDE integration tests (google-gemini#9524)

c97f9b6

Co-authored-by: Shreya Keshive <skeshive@gmail.com>

fix(prompt): Prevent model from reverting successful changes (google-…

7c42b48

…gemini#9253)

Update extension > plugin to avoid confusion (google-gemini#9780)

48102b2

Unset foreground in default themes (google-gemini#9765)

58c68ae

fix(temporary): Don't run ctrl+c exit test on windows (google-gemini#…

b7e938e

…9785)

Create issues on manual release failures similar to other release pro… (

6a358d9

google-gemini#9786)

Add integration test for extensions (google-gemini#9177)

52c486f

Add 'getting started' extensions documentation (google-gemini#9536)

714d029

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

geoffdowns requested a review from a team as a code owner September 26, 2025 00:25

geoffdowns added 3 commits September 25, 2025 17:27

Merge branch 'main' into remove-type-checks

e259db4

Merge branch 'main' into remove-type-checks

8533222

update integration test comment/documentation

238b114

bbiggs approved these changes Sep 26, 2025

View reviewed changes

bbiggs added this pull request to the merge queue Sep 26, 2025

Merged via the queue into google-gemini:main with commit 11c995e Sep 26, 2025
16 of 17 checks passed

geoffdowns mentioned this pull request Sep 26, 2025

Strict JSON schema validation rule in MCP tools #6632

Closed

muhammetakkurtt mentioned this pull request Oct 2, 2025

Fix gemini CLI MCP error with wrong keyword 'schemaVersion' apify/apify-mcp-server#295

Closed

thacio added a commit to thacio/auditaria that referenced this pull request Oct 4, 2025

Merge Commit '11c995e': Stop checking MCP tool schemas for type defin…

6064d0f

…itions (google-gemini#9574)

krasmussen37 mentioned this pull request Nov 18, 2025

Gemini API rejects MCP tool schemas with $defs references #13326

Closed

sripasg added the size/l A large sized PR label Jun 2, 2026

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Stop checking MCP tool schemas for type definitions#9574

Stop checking MCP tool schemas for type definitions#9574
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geoffdowns commented Sep 25, 2025

TLDR

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gemini-code-assist Bot commented Sep 25, 2025

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geoffdowns commented Sep 25, 2025

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