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

Goes well beyond the annotations: it discloses that entries are immutable ('never edited'), that reversal is the only correction path, that tax lines propagate to the tax report, and that the call costs $0.01 with no charge on failure. These are exactly the operational facts a write-tool caller needs and none are in the annotation block.

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?

Front-loaded definition first, then use cases, then lifecycle and cost. Five short sentences, each carrying distinct information with no repetition of schema 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?

For an eight-parameter mutation tool with no output schema, it covers the crucial invariants (balance, minimum lines, immutability, cost). It does not indicate what a successful call returns (e.g., whether an entry id comes back), which matters for follow-up calls to reverse or retrieve it.

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?

Adds real semantics the schema cannot express: the line count minimum, the debit/credit exclusivity, the balancing constraint, and the purpose of the tax field. It leaves some schema-covered-but-undescribed params (memo, reference, party) unaddressed, so it improves on the 63% coverage without fully compensating.

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 ('Book an entry') and immediately pins down the shape of a valid entry: two or more lines, each a debit or credit on an account, and balanced. It also carves out its niche against siblings ('anything the other tools don't cover') and names the reversal tool, so an agent can distinguish it without opening schemas.

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?

Explicit when-to-use via a concrete list of scenarios (opening balances, loan, depreciation, owner's drawings, transfers, corrections) plus a fallback rule for cases other tools don't cover. It also names the alternative for undoing an entry (books_reverse_entry), leaving little to inference.

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