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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds value beyond annotations by disclosing the data source ('Sourced from IMF IFS (keyless)'), which signals no authentication is needed, and by describing the return payload components. No mention of caching or data latency, but with strong annotation coverage the bar is lower and this clears it.

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 tightly written sentences with zero waste: identification and target context first, then return payload, then usage queries, then data source. Each sentence earns its place and the most decision-relevant information (what metric, what 2% target) is front-loaded.

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 simple read-only tool with one optional parameter, the description covers the metric definition, return values, usage scenarios, and data provenance. Minor gaps: the exact shape of the 'recent monthly history' array isn't specified, but with no output schema expected for such a tool and annotations covering safety, this is nearly complete. The keyless note anticipates the auth question agents commonly have.

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 100% — the schema already documents 'months' as 'How many recent months of history to return (default 12).' The description's phrase 'recent monthly history' corroborates the parameter's meaning but adds no new semantic detail beyond what the schema provides. The baseline 3 is appropriate since the schema carries the full burden.

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 uses a specific verb and resource: 'Returns the latest year-on-year inflation rate (%), the latest CPI index level, their month, and recent monthly history.' It precisely defines the metric as Japan's CPI all-items index targeting 2%, which clearly separates it from the adjacent sibling boj_policy_rate. An agent can immediately understand what this tool delivers.

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 explicit when-to-use guidance with concrete query examples: 'Use for "Japan inflation rate" / "Japan CPI" / "is Japan hitting the BOJ 2% target" questions.' This is actionable for an agent selecting the tool. It doesn't explicitly exclude alternatives or name boj_policy_rate as the sibling to use for rate questions, which would make it a 5, but the targeting context implicitly steers the agent correctly.

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