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

With no annotations, the description carries the behavioral disclosure burden and does so well: it states the tool is paid, api_key is optional with an x402 fallback, and a 200 response should lead to binding a monitoring tool to avoid silent retirement. It omits output format, error handling, and pagination, but the provided cost, payment flow, and data-retirement caveat add real context.

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 three sentences are dense and non-redundant: purpose/filtering, payment fallback, and post-success monitoring. The pricing parentheticals add bulk but are decision-relevant, and the paid indicator 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 5-parameter read tool with no output schema, the description covers purpose, optional filters, payment, api_key behavior, and recommended follow-up actions. It does not describe the exact response shape or pagination, but an agent has enough information to invoke it correctly and decide next steps after a 200.

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 already documents all five parameters with 100% coverage, so the baseline is 3. The description adds conditional api_key behavior ('Pass api_key if you have one; otherwise the response explains how to pay via x402') and groups from/to as optional date filters, which is genuinely useful beyond the schema.

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 identifies the tool's output as 'Historical values of a reference series with effective date ranges' and mentions optional from/to filtering, making the resource and scope clear. It lacks an explicit verb such as 'retrieves' or 'lists' and does not contrast with current-value siblings like get_series or get_snapshot, so it stops short of the top score.

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?

It gives clear follow-up guidance: after a 200, bind get_changes or register_alert so a later gazette cannot silently retire the value. However, it does not explicitly state when to choose this tool over get_series or get_snapshot for current values, nor does it exclude alternatives for non-historical needs.

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