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

Beyond the annotations (which indicate non-read-only and non-destructive), the description adds useful behavioral context: 'Nothing is written back' clarifies that source stores are untouched, and 'Free: 3 periods a month' reveals a usage constraint. It does not contradict annotations, and while it doesn't detail idempotency or error semantics, it provides meaningful extra information.

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?

The description is exceptionally concise—three short sentences that front-load the core action, then add the no-write-back clarification and the free-tier limit. Every sentence earns its place with no redundancy.

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 build-oriented tool with no output schema, the description covers the essential context: input sources, scope, registration, and a usage limit. It could mention what happens on re-runs or the output format, but given the complexity and existing schema documentation, it is adequately complete.

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 schema descriptions already fully document the parameters (100% coverage), so the baseline is 3. The description reinforces the currency constraint with 'ONE currency' and aligns with the schema's note that currencies are never added together, but it adds no new semantic detail beyond that.

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 clearly states the tool's purpose: deriving the double-entry ledger for a single period in ONE currency from specific source stores and registering it. It distinguishes itself from siblings by emphasizing that it registers the ledger (not merely reports or exports) and that it's singular currency, which is a unique trait.

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 description provides context about the tool's scope (one period, one currency) and a free-tier limit, but it does not explicitly state when to use this tool versus sibling tools like ledger_report or ledger_export_csv. The phrase 'register it' implies a build action, but no direct comparison is given.

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