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

Annotations already declare read-only, idempotent, and non-destructive. The description adds valuable behavioral context: it performs a live UDP probe to port 443 and notes the expected timing (~2-5s due to UDP handshake timeout). It also implicitly states it is a network operation without stating side effects, which aligns with annotations. It doesn't contradict annotations.

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 concise, front-loaded with the tool's purpose, and every sentence adds value: it lists the three signals, explains the return values, gives use cases, notes exclusions, and mentions auth/timing. No wasted words.

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?

Given the tool's moderate complexity (multiple signals, live probe, timing), the description is reasonably complete. It covers inputs (domain), process (signals), outputs (per-signal verdict plus aggregate boolean), and constraints (no auth, timing). Minor gaps: doesn't detail how failures are reported or whether partial results are returned, but given good annotations and schema, this is acceptable.

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 schema already provides 100% coverage for the single 'domain' parameter, including an example and validation rules (no URL, path, or port). The description echoes the domain-only requirement implicitly by mentioning 'for a domain' but adds no additional semantics beyond the schema. Baseline 3 is appropriate because the schema does the heavy lifting.

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 clearly states it is a read-only HTTP/3 + QUIC support check for a domain, combining three specific signals (Alt-Svc header, HTTPS/SVCB DNS records, live QUIC probe). It distinguishes itself from sibling tools by explicitly naming its unique features and use cases, making it easy to select.

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 clear context on when to use the tool: for validating CDN/Cloudflare HTTP/3 rollouts or auditing modern transport posture, and explicitly states it is not relevant for mail-only domains. However, it does not mention alternatives or when not to use it beyond mail-only domains, which would be stronger guidance.

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