>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3569862. --> Reported by: [yautja_cetanu](https://www.drupal.org/user/626050) Related to !45 >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p> McpPluginBase::generateToolId() enforces a 64-character limit on tool names for MCP client compatibility. However, MCP clients add their own prefix to tool names. For example, Claude Code prepends mcp__{server-name}__ (10-19+ characters), causing the final tool name to exceed 64 characters and triggering API errors:</p> <p> messages.2.content.0.tool_result.content.1.tool_reference.tool_name:<br> String should have at most 64 characters</p> <p> The longest names come from the ToolApi plugin, which replaces : with ___ (triple underscore). For example:</p> <p> - Tool API name: ai_agent_agent:add_default_information_tool<br> - After ToolApi.php:108: ai_agent_agent___add_default_information_tool<br> - After generateToolId(): tools_ai_agent_agent___add_default_information_tool (52 chars)<br> - After Claude Code prefix: mcp__drupal-local__tools_ai_agent_agent___add_default_information_tool (69 chars &mdash; over<br> limit)</p> <h4 id="summary-steps-reproduce">Steps to reproduce</h4> <p>- Install MCP<br> - Install Tool API<br> - Set up the binary MCP server<br> - Try and use the default information tool.</p> <p><a href="https://www.drupalforge.org/template/visual-flow-builder-agents-flowdrop-ui-drupal-cms">https://www.drupalforge.org/template/visual-flow-builder-agents-flowdrop-ui-drupal-cms</a> - example.</p> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p> Suggested fixes</p> <p> 1. Reduce the internal character limit in generateToolId() from 64 to ~50, leaving headroom for the client-side prefix.<br> The docblock already notes this is for client compatibility &mdash; a lower limit would account for the prefix clients add.</p> <p> 2. Use single underscore instead of triple for colon replacement in ToolApi.php:108. Changing str_replace(':', '___',<br> $name) to str_replace(':', '_', $name) saves 2 characters per colon and is still unambiguous since tool names don't<br> naturally contain colons.</p> <p> Workaround</p> <p> Shorten the MCP server name in the client configuration (e.g., dl instead of drupal-local in .mcp.json).</p> <h3 id="summary-remaining-tasks">Remaining tasks</h3> <h3 id="summary-ui-changes">User interface changes</h3> <h3 id="summary-api-changes">API changes</h3> <h3 id="summary-data-model-changes">Data model changes</h3>