tools_cname_lookupFree public API. Resolve a hostname's CNAME chain. Useful for debugging custom-domain CNAME setups.
| Name | Required | Description | Default |
|---|---|---|---|
| host | Yes | Hostname to resolve, e.g. www.example.com. |
| Name | Required | Description | Default |
|---|---|---|---|
| ok | Yes | Always true here; failures return an isError result instead. | |
| data | Yes |
Changes observed during successful MCP inspections.
Output schema / (root)Previous value: -nullNew value: +{
+ "$schema": "http://json-schema.org/draft-07/schema#",
+ "additionalProperties": true,
+ "description": "The hostname's CNAME target and what it resolves to.",
+ "properties": {
+ "data": {
+ "additionalProperties": true,
+ "properties": {
+ "aRecords": {
+ "description": "A records of the target.",
+ "items": {
+ "type": "string"
+ },
+ "type": "array"
+ },
+ "cnames": {
+ "description": "CNAME answers; empty if the host has no CNAME.",
+ "items": {
+ "type": "string"
+ },
+ "type": "array"
+ },
+ "host": {
+ "type": "string"
+ },
+ "isApex": {
+ "type": "boolean"
+ },
+ "target": {
+ "description": "First CNAME target, or null.",
+ "type": [
+ "string",
+ "null"
+ ]
+ }
+ },
+ "required": [
+ "host",
+ "isApex",
+ "cnames",
+ "aRecords"
+ ],
+ "type": "object"
+ },
+ "ok": {
+ "description": "Always true here; failures return an isError result instead.",
+ "type": "boolean"
+ }
+ },
+ "required": [
+ "ok",
+ "data"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds context the annotations cannot: it is a "Free public API," implying no credentials and potentially rate-limited public access. It says nothing about response shape, but the output schema handles that.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Three short sentences, no wasted clauses, with the operation stated first and the access/nature context up front. The final debugging sentence borders on filler but does carry routing value.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a one-parameter read-only lookup with an output schema available, the description covers what the tool does, its access model, and its typical use case. Only the absence of sibling routing keeps it from being fully complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With a single parameter at 100% schema description coverage, the schema already documents the hostname input and its format. The description only echoes "hostname" without adding syntax, chain-depth semantics, or failure behavior, so the baseline 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
"Resolve a hostname's CNAME chain" gives a specific verb plus a precise resource, and the CNAME focus does separate it from generic siblings like tools_dns_record_lookup or tools_txt_record_lookup. It stops short of naming any sibling explicitly, so an agent must still infer which DNS tool to pick.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
"Useful for debugging custom-domain CNAME setups" implies a usage context but offers no when-not guidance and never mentions the overlapping alternatives (dns_record_lookup, dns_propagation_checker) that an agent would weigh against it. Usage is suggested rather than stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.