This MCP server has 20 well-named tools with consistent verb_noun patterns (get_, list_, create_, update_, delete_, send_, reply_) that clearly convey intent. However, significant gaps exist in schema completeness and parameter descriptions. All tools have descriptions (70-450 chars, within the 10-1024 range), but many parameter descriptions are minimal or missing validation details. Input schemas use Zod validation internally but are not fully documented in the tool registration for most tools. Error handling uses custom MessageBirdApiError with helpful HTTP status codes, but recovery guidance is sparse. Tool annotations (readOnlyHint, destructiveHint) are present on most tools, which is excellent. The server clearly follows the chat-data-model principle (accepting phone numbers in E.164 format, natural identifiers) and composition patterns (tools chain well via conversation_id, contact_id, template_name). Output schemas are inferred but not explicitly documented. The main limitation: parameter constraints (enums, ranges, format requirements) are declared in code but not fully surfaced to the LLM in descriptions.

• Add documented JSON Schema output schemas for all tools. Example: get_balance should declare { balance: { type: 'object', properties: { amount: { type: 'number' }, currency: { type: 'string' }, type: { type: 'string', enum: ['prepaid', 'postpaid'] } } } }.
• Refactor list_conversations 'proxy' parameter: split into a clearer description or add an optional 'assignee_status' enum (none, waiting_reply, assigned, assigned_and_waiting). Document limitations upfront.
• For get_contact, explicitly state: 'Provide ONE of: contact_id, msisdn, or name. If multiple provided, contact_id takes precedence.' Add same guidance to parameter descriptions.
• Add min/max constraints to all numeric/array parameters. Example: send_interactive_buttons buttons field should document 'Array of 1-3 button objects' with each button object schema outlined.
• Replace generic error responses with error classification. Catch 429 (rate limit), 404 (not found), 400 (validation), 500 (server) and return actionable messages like 'Rate limited. Retry after 60 seconds.' or 'Contact not found. Try search_contacts to find matching number.'
• For destructive tools (delete_contact, delete_template, delete_template_variant), implement confirmation pattern: return { input_required: 'confirm_delete', confirm_key: 'contact_id_123' } and require the agent to call confirm with the token. This leverages MCP Multi-Round-Trip Requests.
• Add parameter type suffixes for clarity. Rename generic 'offset' and 'limit' to clarify they are numeric strings. Better: accept number type and convert, or document as 'string-encoded integer (e.g., "10")'.