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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, covering safety traits. The description adds one behavioral detail: 'No key required'—an access/authentication trait not captured in annotations. It does not describe output format, error behavior, or rate limits, but for a simple info tool with annotations, this is acceptable yet not highly informative.

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 a single, well-structured sentence that front-loads the primary purpose ('Service description') before enumerating specifics. It contains no redundant words and effectively communicates the tool's scope and the key usage note about authentication.

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 info tool with no output schema, the description is sufficient. It states what the tool returns (pubkey, chain head, free-tier limits) and the critical access requirement (no key). Nothing an agent needs to correctly invoke and interpret this tool 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?

The tool has zero parameters, so the schema trivially covers 100%. The description is not required to explain parameters but instead clarifies the output contents, which is appropriate. It adds value by enumerating the pieces of service information returned, fulfilling the baseline for a parameterless tool.

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 the resource (service info) and lists the specific contents: Ed25519 pubkey, chain head, free-tier limits. It distinguishes itself from siblings by noting 'No key required,' which implies an unauthenticated info endpoint. However, it lacks an explicit verb like 'returns' and does not directly contrast with related tools such as vigil_chain or vigil_pricing.

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 phrase 'No key required' provides a clear usage condition—this tool can be called without authentication, unlike many siblings that likely require keys. However, it does not explicitly state when to prefer this over alternative tools like vigil_chain or vigil_pricing, nor does it mention exclusions or scenarios where this should not be used.

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