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

Adds substantial context beyond the annotations: that entries are never mutated or deleted, how the reversal is dated including the locked-period fallback, that matched bank lines are unmated pending re-match, and that the call costs $0.01 with no charge on failure. This is exactly the side-effect and cost disclosure an agent needs for a non-idempotent write.

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?

Five short sentences, each carrying distinct information, with the core purpose and its rationale front-loaded before the edge cases. No filler and no repetition of schema or annotation content.

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?

With no output schema and only hint annotations, the description covers dating, side effects, invoice interaction, and pricing well. It does not state what the call returns (e.g., the mirror entry's number) or what memo does, which are the remaining gaps for a write tool.

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?

Schema coverage is 67% (entry and date documented, memo not). The description adds real meaning beyond the schema for date by explaining the default resolution order rather than just the YYYY-MM-DD pattern. The memo parameter is never explained in either place.

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?

States a specific verb and resource ("Undo an entry by booking its mirror image") and immediately clarifies the mechanism, so an agent distinguishes it from a delete or edit operation. The parenthetical "entries are never edited or deleted" explicitly separates it from a hypothetical deletion sibling like books_delete_asset.

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?

Gives conditional guidance on dating (entry's date, today if the period is locked, unless date is supplied) and routes invoice-originated entries to the correct alternative behavior (void the invoice or record a refund). It stops short of naming the sibling tools to call for those invoice paths, leaving the agent to infer them.

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