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

Beyond the annotations (mutation, idempotent, non-destructive) it adds genuinely valuable behavior: the lock blocks all tools and invoices on or before the date, null un-locks, every change is preserved in history, and it costs $0.001 per call with no charge on failure. These are the exact concerns (reversibility, cost, side effects) an agent needs and that the annotations alone do not convey.

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 dense sentences with the locking effect front-loaded, followed by reversal, history, and pricing. No filler; every clause adds operational meaning.

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 two-parameter mutation with no output schema, the description covers effect, reversibility, audit history, and cost—more than adequate to call it correctly. The only gap is the undocumented 'reason' parameter.

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?

With 0% schema description coverage the description must carry the parameters. It explains 'through' well—including the important null-unlocks semantic not captured in the pattern-only schema—but says nothing about the 'reason' parameter, leaving one of two params undocumented.

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?

It states a specific verb and resource (lock the books through a date) and describes the concrete effect: nothing new can be booked on or before it by any tool or invoice. The scope is unambiguous, though it never names the closely related sibling books_close_year, which is the main alternative an agent might confuse it with.

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 parenthetical (a closed month, a filed tax return) implies when locking is appropriate, and 'null unlocks' signals the reversal case. But there is no explicit when-not guidance and no routing to alternatives like books_close_year or books_get, leaving the agent to infer usage from context.

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