REA Confirms MCP Schema Compatibility Issue; VS Code May Reject Tools in 6.5.0

On October 17, a community report about reverse engineering agent tool REA revealed an MCP compatibility issue: the server appeared to be running, but its tools could not be used in VS Code Chat. A project collaborator then reproduced the schema issue with the published package and confirmed that a fix is on the main branch but has not yet made it into an official release. Issue report and collaborator verification

REA gives coding agents access to code, references, and runtime observations to investigate application features and reconstruct behavior. The official website demonstrates workflows for native applications, JavaScript, Electron, and browser analysis. As a result, whether a client accepts tool descriptions directly affects whether an agent can begin an investigation. REA official overview

The reported environment was Windows x64, VS Code 1.142.0, and rea-agents 6.5.0. The collaborator listed tools over stdio and found that the nested array in build_call_path used prefixItems to describe elements at fixed positions but did not include items; 22 other tools had the same shape. According to the collaborator's inspection, VS Code's tool schema normalizer rejects this kind of array. The main branch now adds items and includes a check covering the entire tool catalog. Technical verification details

This case shows that MCP integrations need separate validation for process startup, tool discovery, and schema compatibility. Microsoft's documentation explains that VS Code discovers tools provided by a server and then makes them available to chat agents. An engineering implication is to treat “starts successfully” and “available to call” as separate acceptance criteria, and to run client compatibility tests against the release package. VS Code MCP documentation

The available evidence has limits: the collaborator scanned the package and main branch schemas but did not launch VS Code to verify the full workflow; the impact on other clients is also unknown. The next things to watch are when a release with the fix is published and whether tool discovery and actual calls succeed in the original reported environment. For now, this can be treated as a confirmed schema compatibility defect, with the effectiveness of the fix still awaiting end-to-end verification. Current fix status