get_nav_history

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely non-obvious context: data is read from historical blocks on chain, and 'History starts at the deployment of the vault in service' — a real temporal boundary that the annotations do not express.

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 sentences, front-loaded with the core resource and data source before the comparative detail and the temporal caveat. Dense but each clause carries information; only slightly heavy for two optional integer/enum parameters.

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?

An output schema exists, so return-shape explanation is not needed. The description covers contents (change values, max drawdown), provenance (on-chain historical blocks, vault's own oracles), and the start boundary, which is sufficient for a low-complexity two-param read 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 description coverage is 100% (points, interval, defaults, enum all documented in the schema), so the baseline is 3. The description references 'the window' and 'the change of each over the window' but adds no syntax, format, or constraint detail beyond what the schema already states.

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 first sentence names the specific resource (NAV per GBLIN share over time), the data source (read from the chain at past blocks), and the comparative payload (ETH/USD and BTC/USD oracle prices, change over window, largest drawdown). This is far more specific than a sibling like get_treasury_state and lets an agent distinguish it immediately.

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 closing sentence gives a clear use case: 'judge how the index behaved against holding ETH or BTC over the same span.' It conveys when the tool is valuable but does not name alternatives or state when not to use it, so it falls short of the explicit when/when-not/alternative routing that a 5 would require.

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