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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds value beyond that by disclosing that submissions are pending rather than independently confirmed and that no key is needed, which meaningfully shapes expectations.

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 deliver the resource, the pending/unverified caveat, and the authentication requirement with no wasted words. The most important identifying information is front-loaded in the first sentence.

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, idempotent tool, the description is nearly complete: it states what data is exposed, its reliability caveat, and its auth requirement. It would be slightly stronger if it explicitly said that it returns a list or collection, but the plural name and public-scope phrasing largely cover that.

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 and the schema's description coverage is effectively complete, so there is no parameter burden for the description to carry. A baseline of 4 is appropriate because no additional parameter explanation is needed.

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 identifies the resource ('public timestamp submissions to OpenTimestamps calendars') and one key property ('pending, not an independently verified Bitcoin confirmation'), but it never states the actual action, such as 'list' or 'retrieve'. The plural name vigil_anchors hints at a collection operation, yet that is left to inference rather than stated.

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 useful context: the operation is public and 'no key is required,' and the data is unverified. However, it does not explicitly say when to choose this tool over siblings like vigil_anchor or vigil_verify_receipt, nor does it state when not to use it.

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