diff --git a/src/mcp/mcp.c b/src/mcp/mcp.c
index 6a49c9976..374dc8802 100644
--- a/src/mcp/mcp.c
+++ b/src/mcp/mcp.c
@@ -1513,12 +1513,16 @@ static char *handle_query_graph(cbm_mcp_server_t *srv, const char *args) {
 
     if (!query) {
         free(project);
-        return cbm_mcp_text_result("query is required", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"query is required\","
+            "\"hint\":\"Pass a Cypher query string, e.g. MATCH (n:Function) RETURN n.name LIMIT 10\"}", true);
     }
     if (!store) {
         free(project);
         free(query);
-        return cbm_mcp_text_result("{\"error\":\"no project loaded\"}", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"no project loaded\","
+            "\"hint\":\"Run index_repository with repo_path to index the project first.\"}", true);
     }
 
     cbm_cypher_result_t result = {0};
@@ -1689,7 +1693,9 @@ static char *handle_index_status(cbm_mcp_server_t *srv, const char *args) {
 static char *handle_delete_project(cbm_mcp_server_t *srv, const char *args) {
     char *name = cbm_mcp_get_string_arg(args, "project_name");
     if (!name) {
-        return cbm_mcp_text_result("project_name is required", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"project_name is required\","
+            "\"hint\":\"Pass the project name to delete. Use list_projects to see available projects.\"}", true);
     }
 
     /* Close store if it's the project being deleted */
@@ -1847,13 +1853,17 @@ static char *handle_trace_call_path(cbm_mcp_server_t *srv, const char *args) {
     if (!func_name) {
         free(project);
         free(direction);
-        return cbm_mcp_text_result("function_name is required", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"function_name is required\","
+            "\"hint\":\"Pass the name of a function to trace, e.g. {\\\"function_name\\\":\\\"main\\\"}\"}", true);
     }
     if (!store) {
         free(func_name);
         free(project);
         free(direction);
-        return cbm_mcp_text_result("{\"error\":\"no project loaded\"}", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"no project loaded\","
+            "\"hint\":\"Run index_repository with repo_path to index the project first.\"}", true);
     }
     if (!direction) {
         direction = heap_strdup("both");
@@ -1865,11 +1875,15 @@ static char *handle_trace_call_path(cbm_mcp_server_t *srv, const char *args) {
     cbm_store_find_nodes_by_name(store, project, func_name, &nodes, &node_count);
 
     if (node_count == 0) {
+        char errbuf[512];
+        snprintf(errbuf, sizeof(errbuf),
+            "{\"error\":\"function not found: '%s'\","
+            "\"hint\":\"Use search_code_graph with name_pattern to find similar symbols.\"}", func_name);
         free(func_name);
         free(project);
         free(direction);
         cbm_store_free_nodes(nodes, 0);
-        return cbm_mcp_text_result("{\"error\":\"function not found\"}", true);
+        return cbm_mcp_text_result(errbuf, true);
     }
 
     yyjson_mut_doc *doc = yyjson_mut_doc_new(NULL);
@@ -2109,7 +2123,9 @@ static char *handle_index_repository(cbm_mcp_server_t *srv, const char *args) {
 
     if (!repo_path) {
         free(mode_str);
-        return cbm_mcp_text_result("repo_path is required", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"repo_path is required\","
+            "\"hint\":\"Pass the absolute path to the project root directory.\"}", true);
     }
 
     cbm_index_mode_t mode = CBM_MODE_FULL;
@@ -2121,7 +2137,9 @@ static char *handle_index_repository(cbm_mcp_server_t *srv, const char *args) {
     cbm_pipeline_t *p = cbm_pipeline_new(repo_path, NULL, mode);
     if (!p) {
         free(repo_path);
-        return cbm_mcp_text_result("failed to create pipeline", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"failed to create indexing pipeline\","
+            "\"hint\":\"Check that repo_path exists and is readable. The directory may be empty or inaccessible.\"}", true);
     }
 
     char *project_name = heap_strdup(cbm_pipeline_project_name(p));
@@ -2463,13 +2481,18 @@ static char *handle_get_code_snippet(cbm_mcp_server_t *srv, const char *args) {
     if (!qn) {
         free(project);
         free(snippet_mode);
-        return cbm_mcp_text_result("qualified_name is required", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"qualified_name is required\","
+            "\"hint\":\"Pass a symbol qualified name, e.g. {\\\"qualified_name\\\":\\\"myapp.src.main.handle_request\\\"}. "
+            "Use search_code_graph to find qualified names.\"}", true);
     }
     if (!store) {
         free(qn);
         free(project);
         free(snippet_mode);
-        return cbm_mcp_text_result("{\"error\":\"no project loaded\"}", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"no project loaded\","
+            "\"hint\":\"Run index_repository with repo_path to index the project first.\"}", true);
     }
 
     /* Tier 1: Exact QN match */
@@ -2653,10 +2676,16 @@ static char *handle_get_code_snippet(cbm_mcp_server_t *srv, const char *args) {
     cbm_store_search_free(&search_out);
 
     /* Nothing found */
-    free(qn);
-    free(project);
-    free(snippet_mode);
-    return cbm_mcp_text_result("symbol not found", true);
+    {
+        char errbuf[512];
+        snprintf(errbuf, sizeof(errbuf),
+            "{\"error\":\"symbol not found: '%s'\","
+            "\"hint\":\"Use search_code_graph with name_pattern to find the correct qualified_name.\"}", qn);
+        free(qn);
+        free(project);
+        free(snippet_mode);
+        return cbm_mcp_text_result(errbuf, true);
+    }
 }
 
 /* ── search_code ──────────────────────────────────────────────── */
@@ -2673,7 +2702,9 @@ static char *handle_search_code(cbm_mcp_server_t *srv, const char *args) {
     if (!pattern) {
         free(project);
         free(file_pattern);
-        return cbm_mcp_text_result("pattern is required", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"pattern is required\","
+            "\"hint\":\"Pass a text pattern or regex (with regex:true) to search source code.\"}", true);
     }
 
     char *root_path = get_project_root(srv, project);
@@ -2681,7 +2712,10 @@ static char *handle_search_code(cbm_mcp_server_t *srv, const char *args) {
         free(pattern);
         free(project);
         free(file_pattern);
-        return cbm_mcp_text_result("project not found or not indexed", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"project not found or not indexed\","
+            "\"hint\":\"Run index_repository with repo_path to index the project first, "
+            "or use list_projects to see available projects.\"}", true);
     }
 
     /* Write pattern to temp file to avoid shell injection */
@@ -2697,7 +2731,9 @@ static char *handle_search_code(cbm_mcp_server_t *srv, const char *args) {
         free(pattern);
         free(project);
         free(file_pattern);
-        return cbm_mcp_text_result("search failed: temp file", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"search failed: could not create temp file\","
+            "\"hint\":\"Check that /tmp is writable and has disk space.\"}", true);
     }
     // NOLINTNEXTLINE(clang-analyzer-security.insecureAPI.DeprecatedOrUnsafeBufferHandling)
     (void)fprintf(tf, "%s\n", pattern);
@@ -2734,7 +2770,9 @@ static char *handle_search_code(cbm_mcp_server_t *srv, const char *args) {
         free(pattern);
         free(project);
         free(file_pattern);
-        return cbm_mcp_text_result("search failed", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"search failed: grep command could not execute\","
+            "\"hint\":\"Check that grep is installed and the project root directory exists.\"}", true);
     }
 
     yyjson_mut_doc *doc = yyjson_mut_doc_new(NULL);
@@ -2819,7 +2857,10 @@ static char *handle_detect_changes(cbm_mcp_server_t *srv, const char *args) {
     if (!root_path) {
         free(project);
         free(base_branch);
-        return cbm_mcp_text_result("project not found", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"project not found\","
+            "\"hint\":\"Run index_repository with repo_path to index the project first, "
+            "or use list_projects to see available projects.\"}", true);
     }
 
     /* Get changed files via git */
@@ -2835,7 +2876,9 @@ static char *handle_detect_changes(cbm_mcp_server_t *srv, const char *args) {
         free(root_path);
         free(project);
         free(base_branch);
-        return cbm_mcp_text_result("git diff failed", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"git diff failed\","
+            "\"hint\":\"Check that git is installed and the project is a git repository.\"}", true);
     }
 
     yyjson_mut_doc *doc = yyjson_mut_doc_new(NULL);
@@ -2914,7 +2957,10 @@ static char *handle_manage_adr(cbm_mcp_server_t *srv, const char *args) {
         free(project);
         free(mode_str);
         free(content);
-        return cbm_mcp_text_result("project not found", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"project not found\","
+            "\"hint\":\"Run index_repository with repo_path to index the project first, "
+            "or use list_projects to see available projects.\"}", true);
     }
 
     char adr_dir[4096];
@@ -3172,7 +3218,10 @@ static char *handle_index_dependencies(cbm_mcp_server_t *srv, const char *args)
 // NOLINTNEXTLINE(bugprone-easily-swappable-parameters)
 char *cbm_mcp_handle_tool(cbm_mcp_server_t *srv, const char *tool_name, const char *args_json) {
     if (!tool_name) {
-        return cbm_mcp_text_result("missing tool name", true);
+        return cbm_mcp_text_result(
+            "{\"error\":\"missing tool name\","
+            "\"hint\":\"Available tools: search_code_graph, trace_call_path, get_code. "
+            "Use tools/list to see all available tools.\"}", true);
     }
 
     /* Phase 9: consolidated tool names (streamlined mode) */
@@ -3238,8 +3287,11 @@ char *cbm_mcp_handle_tool(cbm_mcp_server_t *srv, const char *tool_name, const ch
         return handle_index_dependencies(srv, args_json);
     }
 
-    char msg[256];
-    snprintf(msg, sizeof(msg), "unknown tool: %s", tool_name);
+    char msg[512];
+    snprintf(msg, sizeof(msg),
+        "{\"error\":\"unknown tool: '%s'\","
+        "\"hint\":\"Available tools: search_code_graph, trace_call_path, get_code. "
+        "Use tools/list to see all available tools.\"}", tool_name);
     return cbm_mcp_text_result(msg, true);
 }
 
diff --git a/tests/test_tool_consolidation.c b/tests/test_tool_consolidation.c
index 29ebf5c81..985b3284b 100644
--- a/tests/test_tool_consolidation.c
+++ b/tests/test_tool_consolidation.c
@@ -421,6 +421,305 @@ TEST(no_resources_capability_gets_context_injection) {
     PASS();
 }
 
+/* ── 8. MCP spec compliance tests ─────────────────────────── */
+
+TEST(initialize_response_has_protocol_version) {
+    char *resp = cbm_mcp_initialize_response();
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "protocolVersion"));
+    ASSERT_NOT_NULL(strstr(resp, "2024-11-05"));
+    ASSERT_NOT_NULL(strstr(resp, "serverInfo"));
+    ASSERT_NOT_NULL(strstr(resp, "codebase-memory-mcp"));
+    free(resp);
+    PASS();
+}
+
+TEST(initialize_resources_cap_subscribe_false) {
+    /* Server must advertise subscribe:false (we don't support per-resource subscriptions) */
+    char *resp = cbm_mcp_initialize_response();
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "\"subscribe\":false"));
+    ASSERT_NOT_NULL(strstr(resp, "\"listChanged\":true"));
+    free(resp);
+    PASS();
+}
+
+TEST(resources_list_has_mimeType_and_description) {
+    /* MCP spec requires name, uri; recommends description and mimeType */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"resources/list\"}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "mimeType"));
+    ASSERT_NOT_NULL(strstr(resp, "application/json"));
+    ASSERT_NOT_NULL(strstr(resp, "description"));
+    ASSERT_NOT_NULL(strstr(resp, "name"));
+    free(resp);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(resources_read_response_has_contents_array) {
+    /* MCP spec: resources/read returns {contents: [{uri, mimeType, text}]} */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"resources/read\","
+        "\"params\":{\"uri\":\"codebase://status\"}}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "\"contents\""));
+    ASSERT_NOT_NULL(strstr(resp, "\"uri\""));
+    ASSERT_NOT_NULL(strstr(resp, "\"mimeType\""));
+    ASSERT_NOT_NULL(strstr(resp, "\"text\""));
+    free(resp);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(resources_read_missing_uri_param) {
+    /* resources/read with no uri → error -32602 (invalid params) */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"resources/read\","
+        "\"params\":{}}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "error"));
+    ASSERT_NOT_NULL(strstr(resp, "Missing uri"));
+    free(resp);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(resources_read_no_params_at_all) {
+    /* resources/read with no params object */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"resources/read\"}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "error"));
+    free(resp);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+/* ── 9. Client behavioral difference tests ───────────────── */
+
+TEST(resource_client_never_gets_context_across_multiple_calls) {
+    /* Resource-capable client should NEVER see _context, even across many calls */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\","
+        "\"params\":{\"protocolVersion\":\"2024-11-05\","
+        "\"capabilities\":{\"resources\":{}},"
+        "\"clientInfo\":{\"name\":\"modern\",\"version\":\"2.0\"}}}");
+    ASSERT_NOT_NULL(resp);
+    free(resp);
+
+    /* 3 consecutive tool calls — none should have _context */
+    for (int i = 0; i < 3; i++) {
+        char *r = cbm_mcp_handle_tool(srv, "search_graph",
+            "{\"name_pattern\":\"test\"}");
+        ASSERT_NOT_NULL(r);
+        ASSERT_NULL(strstr(r, "_context"));
+        /* But session_project should always be present */
+        ASSERT_NOT_NULL(strstr(r, "session_project"));
+        free(r);
+    }
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(legacy_client_gets_context_only_on_first_call) {
+    /* Legacy client: _context on first call, NOT on subsequent calls */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\","
+        "\"params\":{\"protocolVersion\":\"2024-11-05\","
+        "\"capabilities\":{},"
+        "\"clientInfo\":{\"name\":\"legacy\",\"version\":\"1.0\"}}}");
+    ASSERT_NOT_NULL(resp);
+    free(resp);
+
+    /* First call: MUST have _context */
+    char *r1 = cbm_mcp_handle_tool(srv, "search_graph",
+        "{\"name_pattern\":\"test\"}");
+    ASSERT_NOT_NULL(r1);
+    ASSERT_NOT_NULL(strstr(r1, "_context"));
+    free(r1);
+
+    /* Second call: must NOT have _context (one-shot) */
+    char *r2 = cbm_mcp_handle_tool(srv, "search_graph",
+        "{\"name_pattern\":\"test2\"}");
+    ASSERT_NOT_NULL(r2);
+    ASSERT_NULL(strstr(r2, "_context"));
+    ASSERT_NOT_NULL(strstr(r2, "session_project"));
+    free(r2);
+
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(empty_resources_capability_counts_as_support) {
+    /* MCP spec: capabilities.resources:{} means resources supported
+     * (neither subscribe nor listChanged, but resources protocol works) */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\","
+        "\"params\":{\"protocolVersion\":\"2024-11-05\","
+        "\"capabilities\":{\"resources\":{}},"
+        "\"clientInfo\":{\"name\":\"minimal\",\"version\":\"1.0\"}}}");
+    ASSERT_NOT_NULL(resp);
+    free(resp);
+
+    /* Empty resources:{} still means client supports resources → no _context */
+    char *r = cbm_mcp_handle_tool(srv, "search_graph",
+        "{\"name_pattern\":\"x\"}");
+    ASSERT_NOT_NULL(r);
+    ASSERT_NULL(strstr(r, "_context"));
+    free(r);
+
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(no_initialize_defaults_to_legacy_behavior) {
+    /* Server with no initialize call → defaults to legacy (no resources) */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    /* Call tool directly without initialize → should get _context (legacy) */
+    char *r = cbm_mcp_handle_tool(srv, "search_graph",
+        "{\"name_pattern\":\"x\"}");
+    ASSERT_NOT_NULL(r);
+    ASSERT_NOT_NULL(strstr(r, "_context"));
+    free(r);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+/* ── 10. Error message quality tests ─────────────────────── */
+
+TEST(error_no_project_loaded_has_hint) {
+    /* search_graph with a nonexistent project name → resolve_store returns NULL
+     * but cbm_mcp_server_new creates a default store. Use a project name that
+     * won't match any DB file to trigger the error. The REQUIRE_STORE macro
+     * in search_graph handles auto-index, but for a fake project path it will
+     * still fail and return the hint. Test via the error structure in trace. */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    /* trace_call_path goes through REQUIRE_STORE → no project loaded if store NULL.
+     * With cbm_mcp_server_new(NULL), resolve_store(NULL) returns the default store.
+     * The function_not_found error (which also has hint) tests the pattern. */
+    char *r = cbm_mcp_handle_tool(srv, "trace_call_path",
+        "{\"function_name\":\"nonexistent_fn\"}");
+    ASSERT_NOT_NULL(r);
+    /* The response should have a hint field (either "no project loaded" or "not found") */
+    ASSERT_NOT_NULL(strstr(r, "hint"));
+    free(r);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(error_function_not_found_includes_name) {
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *r = cbm_mcp_handle_tool(srv, "trace_call_path",
+        "{\"function_name\":\"nonexistent_xyz_func\"}");
+    ASSERT_NOT_NULL(r);
+    /* Error should include the function name that was searched for */
+    ASSERT_NOT_NULL(strstr(r, "nonexistent_xyz_func"));
+    ASSERT_NOT_NULL(strstr(r, "hint"));
+    free(r);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(error_symbol_not_found_includes_qn) {
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *r = cbm_mcp_handle_tool(srv, "get_code_snippet",
+        "{\"qualified_name\":\"nonexistent.module.func_xyz\"}");
+    ASSERT_NOT_NULL(r);
+    /* Error should include the qualified name that was searched for */
+    ASSERT_NOT_NULL(strstr(r, "nonexistent.module.func_xyz"));
+    ASSERT_NOT_NULL(strstr(r, "hint"));
+    free(r);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(error_missing_required_param_has_hint) {
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+
+    /* query_graph missing query param */
+    char *r1 = cbm_mcp_handle_tool(srv, "query_graph", "{}");
+    ASSERT_NOT_NULL(r1);
+    ASSERT_NOT_NULL(strstr(r1, "query is required"));
+    ASSERT_NOT_NULL(strstr(r1, "hint"));
+    free(r1);
+
+    /* trace_call_path missing function_name */
+    char *r2 = cbm_mcp_handle_tool(srv, "trace_call_path", "{}");
+    ASSERT_NOT_NULL(r2);
+    ASSERT_NOT_NULL(strstr(r2, "function_name is required"));
+    ASSERT_NOT_NULL(strstr(r2, "hint"));
+    free(r2);
+
+    /* get_code_snippet missing qualified_name */
+    char *r3 = cbm_mcp_handle_tool(srv, "get_code_snippet", "{}");
+    ASSERT_NOT_NULL(r3);
+    ASSERT_NOT_NULL(strstr(r3, "qualified_name is required"));
+    ASSERT_NOT_NULL(strstr(r3, "hint"));
+    free(r3);
+
+    /* search_code missing pattern */
+    char *r4 = cbm_mcp_handle_tool(srv, "search_code", "{}");
+    ASSERT_NOT_NULL(r4);
+    ASSERT_NOT_NULL(strstr(r4, "pattern is required"));
+    ASSERT_NOT_NULL(strstr(r4, "hint"));
+    free(r4);
+
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(error_unknown_tool_lists_valid_tools) {
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *r = cbm_mcp_handle_tool(srv, "nonexistent_tool_xyz", "{}");
+    ASSERT_NOT_NULL(r);
+    ASSERT_NOT_NULL(strstr(r, "nonexistent_tool_xyz"));
+    ASSERT_NOT_NULL(strstr(r, "hint"));
+    ASSERT_NOT_NULL(strstr(r, "search_code_graph"));
+    ASSERT_NOT_NULL(strstr(r, "tools/list"));
+    free(r);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
+TEST(error_resource_not_found_has_spec_code) {
+    /* MCP spec: resource not found = -32002 with actionable message */
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    ASSERT_NOT_NULL(srv);
+    char *resp = cbm_mcp_server_handle(srv,
+        "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"resources/read\","
+        "\"params\":{\"uri\":\"codebase://bad_uri_xyz\"}}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_NOT_NULL(strstr(resp, "-32002"));
+    ASSERT_NOT_NULL(strstr(resp, "bad_uri_xyz"));
+    ASSERT_NOT_NULL(strstr(resp, "codebase://schema"));
+    ASSERT_NOT_NULL(strstr(resp, "resources/list"));
+    free(resp);
+    cbm_mcp_server_free(srv);
+    PASS();
+}
+
 /* ── Suite registration ──────────────────────────────────── */
 
 SUITE(tool_consolidation) {
@@ -455,4 +754,23 @@ SUITE(tool_consolidation) {
     RUN_TEST(initialize_advertises_resources_capability);
     RUN_TEST(initialize_parses_client_resources_capability);
     RUN_TEST(no_resources_capability_gets_context_injection);
+    /* MCP spec compliance */
+    RUN_TEST(initialize_response_has_protocol_version);
+    RUN_TEST(initialize_resources_cap_subscribe_false);
+    RUN_TEST(resources_list_has_mimeType_and_description);
+    RUN_TEST(resources_read_response_has_contents_array);
+    RUN_TEST(resources_read_missing_uri_param);
+    RUN_TEST(resources_read_no_params_at_all);
+    /* Client behavioral differences */
+    RUN_TEST(resource_client_never_gets_context_across_multiple_calls);
+    RUN_TEST(legacy_client_gets_context_only_on_first_call);
+    RUN_TEST(empty_resources_capability_counts_as_support);
+    RUN_TEST(no_initialize_defaults_to_legacy_behavior);
+    /* Error message quality */
+    RUN_TEST(error_no_project_loaded_has_hint);
+    RUN_TEST(error_function_not_found_includes_name);
+    RUN_TEST(error_symbol_not_found_includes_qn);
+    RUN_TEST(error_missing_required_param_has_hint);
+    RUN_TEST(error_unknown_tool_lists_valid_tools);
+    RUN_TEST(error_resource_not_found_has_spec_code);
 }