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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely new behavior: the data source is an append-only log answered from HISTOR's own observations with no contact with the target server — useful context that qualifies the openWorldHint and tells the agent results may be stale relative to live state.

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 action and the resource, then the behavioral qualifier. No filler, no repetition of the title.

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?

With no output schema, the description usefully enumerates the three things a lookup returns, which is exactly what the agent needs. The one gap: both parameters are optional and the description never says that at least one identifier (name or endpoint) must be supplied to find anything.

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% and both parameters carry their own descriptions (including the registry-name example), so the schema does the heavy lifting. The prose adds no format or selection guidance beyond that, making the baseline 3 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 ('look up') and resource (an MCP server in HISTOR), and even enumerates the payload it returns: first-pinned time, change frequency, and pattern-scan findings. It does not, however, distinguish itself from the siblings (warden_scan in particular sounds like the active-scan counterpart), leaving that differentiation to inference.

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?

Usage is implied by the lookup semantics, and the sentence 'HISTOR answers from its own observations and never contacts the server' hints at when this is preferable to a live scan. But there is no explicit when-to-use, when-not, or named alternative among tool_list_cost, warden_scan, or x402_check.

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