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

Although annotations already declare readOnlyHint and idempotentHint, the description adds valuable behavioral context: 'COST: free, reads stored data only' and the limitation that no result should be expected with only one audit. This goes beyond the structured annotations and clarifies side-effect-free behavior.

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 and then adds targeted usage and exclusion guidance. Every sentence serves a purpose: what it does, when to call it, when not to call it, and what it costs behaviorally.

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 single-parameter read-only tool with no output schema, the description covers the operation, expected output highlights, prerequisite conditions, and exclusions. An agent has enough information to decide when to call it and what to expect.

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 the single 'url' parameter with 100% coverage, including the requirement of at least two stored audits. The description reinforces 'one URL' and the prerequisite of a fresh audit, but does not add substantial new parameter-level detail beyond what the schema provides.

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 and resource: 'Compares the two most recent stored audits of one URL: grade and score movement, which checks improved, which regressed.' This clearly distinguishes lekta_diff from its siblings and communicates exactly what the tool computes.

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 positive usage: 'USE THIS after a deploy plus a fresh lekta_audit' and 'call it after re-auditing to prove a fix worked.' It also gives explicit negative constraints: 'DO NOT use it to compare two different URLs, and do not expect a result 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.