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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds important behavioral context beyond that: the dual output mode (chart vs. text), which may affect how the agent should present results. It does not mention pagination or error behavior, but for a read-only trend tool this is solid.

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 front-loaded with the core purpose, then provides metric definition and prerequisite. Every sentence earns its place, though the metric explanation could be considered slightly verbose for an agent already familiar with FCI. Still efficient overall.

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?

Given no output schema, the description fully explains what the tool returns (a chart or text summary of FCI history) and provides interpretation guidance for the metric values. It also covers the prerequisite for the required parameter. Nothing essential is missing.

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% — both site_id and days are fully documented in the schema, including defaults and bounds. The description reinforces that site_id must be resolved via list_sites, which is helpful but not additional semantic information beyond the schema. Baseline 3 is appropriate.

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 (Show) and resource (one site's FCI history), clarifies output format (chart in MCP Apps clients, text elsewhere), and defines the metric with its formula and interpretation bands. An agent can distinguish this from list_site_fci_history or get_site_fci_history_entry 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?

Explicitly directs the agent to resolve site_id with list_sites first, and explains what happens in non-chart-rendering clients. This is exactly the kind of prerequisite and environment-aware guidance an agent needs to invoke correctly.

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