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

Annotations already state readOnlyHint=true; the description adds value by disclosing cost ('pure CPU, no network'), reinforcing read-only behavior, and detailing the exact scope of parsing (including T.38 fax attributes). It does not cover error handling or edge cases, but for a read-only parser with annotations covering safety, this is solid context.

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 structured with a cost/read-only line, a concise first sentence, a 'Useful for' paragraph, and a 'Pair with' list. Every sentence earns its place, front-loading the purpose before usage context. No fluff or redundancy.

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 single-parameter tool with no output schema, the description thoroughly enumerates return fields, includes practical use cases, and names sibling tools for further analysis. It even covers niche fax (T.38) negotiation details, making it complete for the tool's complexity.

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?

The input schema has 100% description coverage for the single 'sdp' parameter, already explaining it is the body after the empty line. The tool description does not add param-specific details beyond that, so the baseline 3 applies since the schema carries the semantic weight.

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 ('Parse') and resource ('Session Description Protocol body') and enumerates the structured output fields (origin, session, timing, codecs, DTLS, ICE, fax-relay, crypto). It clearly distinguishes itself from siblings like compare_sdp_offer_answer and parse_sip_message by focusing on SDP payload parsing.

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 explicitly says when to use it: 'debugging WebRTC ↔ SIP interop' and 'inspecting fax negotiation' without re-deriving SDP grammar. It names sibling tools for related scenarios: compare_sdp_offer_answer for both halves, webrtc_sip_checklist for bridge-config. This provides clear when/when-not guidance.

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