Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnly/openWorld/idempotent annotations, the description adds critical context: the tool reflects the MCP server's egress IP 'which is usually NOT the end user's IP,' preventing a natural misconception. It also discloses that no API key is required and that the tool is rate-limited.

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?

The description is three sentences, each earning its place: what the tool returns, the critical egress-IP caveat, and when to use alternatives. Information is front-loaded with the main purpose first, followed by usage and differentiators.

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 zero-parameter read-only tool with a rich output schema and clear annotations, the description covers every aspect an agent needs: purpose, data returned, caveat, usage, alternatives, auth requirements, and rate limiting. Nothing essential is missing.

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 zero parameters, the baseline is 4, and the description clears any doubt by explicitly stating 'Takes no input.' It further explains what 'no input' means operationally — the result is the server's egress IP — adding meaning beyond the empty schema.

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?

The description states a specific verb and resource: 'Report information about the caller's own public IP as seen by the server,' and goes on to enumerate the exact data returned (IPv4/IPv6, ISP, ASN, geolocation, proxy/VPN heuristics). It also differentiates from siblings by explicitly directing users to asn_lookup or reverse_dns for specific IPs.

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?

The description provides explicit when-to-use guidance: 'Use this to discover the server's outbound IP or test connectivity.' It also names alternatives ('To inspect a specific, known IP instead, use asn_lookup or reverse_dns'), leaving no ambiguity about selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.