AgentFixboard
Fixed (verified)Last checked browser-use#schema#tool-calls

MCP browser_click oneOf makes the session return 400

Registering browser-use --mcp fails the whole tool list with 400 tools.N.custom.input_schema: input_schema does not support oneOf, allOf, or anyOf at the top level.

From GitHub

browser-use/browser-use

IssuePull request

Difficulty
Moderate
Time
~15 min
Steps
3
Fixed in
0.12.6
Last checked

Verified fix: PR #4212 merged on . Fixed in 0.12.6 (first published release whose tag contains the merge commit). Last checked .

Symptom

Registering browser-use --mcp fails the whole tool list with 400 tools.N.custom.input_schema: input_schema does not support oneOf, allOf, or anyOf at the top level.

Evidence what you'll see

  • The browser_click input schema in 0.11.13 has a top-level oneOf of {"required": ["index"]} or {"required": ["coordinate_x", "coordinate_y"]}.
  • A comment on 0.12.2 shows the same rejection as API Error: 400 — tools.30.custom.input_schema: input_schema does not support oneOf, allOf, or anyOf at the top level.
  • The report says every MCP tool in the same config fails, not only browser_click, because the tool list is refused and later indexes shift.

Why it happens

Some clients refuse oneOf, allOf, and anyOf at the top of a tool's input schema. browser_click used oneOf to say "pass index, or pass both coordinates." That one schema makes the client reject the whole list, so tools from other servers in the same config disappear with it. The click handler already checked the arguments itself, so the schema keyword was not what enforced the rule at runtime.

Affected versions

browser-use 0.11.13, where the report says the oneOf block was introduced. The report says 0.11.9 does not show it. A comment still sees the 400 on 0.12.2.

Fix steps

0 of 3 done

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How to check it worked

  • Start the same MCP config. The client no longer returns input_schema does not support oneOf, allOf, or anyOf at the top level, and browser_click is listed with the other tools.

If it still fails

  • A click with neither index nor both coordinates still returns Error: Provide either index or both coordinate_x and coordinate_y. That string is the runtime guard, and pull request #4212 does not remove it.
  • The linked issue does not name another tool in this server that still publishes a top-level oneOf.

Sources and credit

Summarized in our own words from these public reports. Credit goes to their authors.

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