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

Annotations already declare readOnlyHint=false, destructiveHint=false, openWorldHint=false and idempotentHint=false, so the safety profile is partly given. The description adds two things the annotations cannot: that nothing is written back to the source stores (resolving the tension between 'register it' and readOnly=false), and a concrete quota of 3 periods per month. It still does not say what a second identical call does, despite non-idempotent being hinted.

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?

Two tightly packed sentences, front-loaded with the verb and resource, then the source stores, then the write-scope and quota caveats. No filler or repetition of the title.

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?

Covers inputs and write scope well, and there is no output schema to restate. But with no output schema the description should indicate what a successful run yields (ledger id, line count, status), and it says only 'register it'; non-idempotent re-run behavior is also left for the agent to infer.

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 description coverage is 100%, with both 'from'/'to' formats and the conditional currency rule already documented in the schema. The description reinforces 'ONE currency' and the no-conversion rule, but adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 ('Derive') and resource ('the double-entry ledger for one period in ONE currency'), names every source store it aggregates, and adds that it 'registers' the result. This clearly separates it from siblings such as ledger_lines, ledger_report, trial_balance and month_close.

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?

Implies usage through the period/currency scoping and the quota note ('Free: 3 periods a month'), which signals a per-period batch operation. However, it never says when to prefer ledger_build over ledger_report, trial_balance or month_close, and gives no prerequisites or exclusions despite a rich sibling set.

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