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 covered. The description adds context about the nature of the content (primary sources, newspapers, memoirs, etc.), which goes beyond the schema and helps the agent understand what kind of data to expect. There is no contradiction with annotations.

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, no filler. The first sentence states the action and object, the second gives the use case. It is front-loaded with the core purpose and uses space efficiently.

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?

This is a simple, read-only tool with one parameter, a well-documented schema, and an output schema present. The description fully covers when to use it and what it returns, while annotations cover safety. Nothing an agent needs to call it correctly 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?

The input schema has 100% description coverage; the 'book' parameter's description already explains it chooses the guide. The tool description adds minimal new meaning—it mentions the guides are by Spencer Hofman but doesn't elaborate on the parameter beyond what the schema provides. Baseline of 3 is correct since the schema does the heavy lifting.

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 states a specific verb ('Return'), the exact resource (the Sources and Further Reading section from Spencer Hofmans' historical companion guides), and the topic scope (1798 or nineteenth-century Irish history). This clearly differentiates it from siblings like get_guide, get_historical_figure, and search_history, which serve other purposes.

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 gives explicit guidance on when to use the tool: 'Use this for questions about primary sources, contemporary newspapers, memoirs, archival records, historical scholarship and further reading...' This is clear context, though it does not explicitly state when not to use it or mention alternatives. Since it covers the key use case, a 4 is appropriate.

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