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

Annotations already declare readOnlyHint=true and destructiveHint=false; the description adds that the tool is 'free' and 'reads stored data only,' and discloses a hard precondition: no result when only one audit exists. This is useful context beyond the annotations, though the core safety profile is already covered by them.

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 what the tool does, then gives usage and exclusion guidance. It is slightly redundant—'call it after re-auditing' and 'USE THIS after a deploy plus a fresh lekta_audit' overlap—but still economical and well structured.

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 one documented parameter, no output schema, and clear annotations, the description covers what the tool returns, when to use it, when not to use it, preconditions, and cost. Nothing essential for an agent to select and invoke 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?

Schema coverage is 100% for the single 'url' parameter, so the baseline is 3. The description adds meaningful semantic clarification that only one URL may be passed and that the tool compares audits within that URL's own history, not two separate URLs. This prevents a natural misunderstanding for a diff-like tool.

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 uses a specific verb and resource: 'Compares the two most recent stored audits of one URL' and names the concrete outputs: 'grade and score movement, which checks improved, which regressed.' This clearly distinguishes lekta_diff from siblings like lekta_audit or lekta_report.

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 when-to-use guidance: 'call it after re-auditing to prove a fix worked' and 'USE THIS after a deploy plus a fresh lekta_audit.' It also gives exclusions: 'DO NOT use it to compare two different URLs' and warns that a result should not be expected when only one audit exists.

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