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

With no annotations, the description carries the full behavioral burden. It discloses the output shape ({ok, next, epochMs}), the UTC basis, supported cron features, and a distinctive side effect: a $0.001 USDC cost on Base per call. It does not mention invalid-expression error behavior, but otherwise gives solid behavioral 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?

Three short sentences, each earning its place: the core computation, the request/response body shape, and the cost. The most 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?

Given the output schema exists and the description already names the response fields, the definition is nearly complete. The main gaps are error behavior and execution details for the paid Base transaction, but the cost disclosure plus input/output summary cover the essentials.

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 already covers both parameters at 100%, including the 'after' default. The description adds little beyond calling expr a '5-field cron expression' and echoing 'after?' in the body format, so it does not meaningfully improve on the 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 uses a specific verb ('Computes') and resource ('next UTC fire time for a 5-field cron expression'), and enumerates supported syntax features. This clearly differentiates it from all sibling tools, which are unrelated utilities like DNS lookup and email validation.

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 purpose is so specific that an agent can infer when to use it: whenever a cron schedule's next fire time is needed. It provides clear context but no explicit exclusion or alternative routing; however, none of the sibling tools compete with this function.

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