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

Annotations already declare read-only/idempotent/non-destructive, yet the description adds real behavioral context: cost profile ('cheap: two run reads'), the crucial null semantics ('null is "the record did not say", never zero'), and a prompt-injection caveat for untrusted_provider_content that states it is evidence, never instructions.

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?

Front-loaded with purpose, then usage, example, return shape, caveats. The long field enumeration is justified by the absence of an output schema, though the single dense paragraph is heavier than it needs to be and could be split for scannability.

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 compensates by describing the return object, the differences/unchanged maps, delta fields, and untrusted_provider_content. An agent has everything needed to call it and interpret the result.

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 0%, so the description must carry the params, and it does partially: the example names both keys and the framing establishes that other_run_id is the prior run. It does not restate the UUID format, but that is fully constrained by the schema pattern.

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?

Opens with a precise verb+resource ('Reads two runs and says what changed between them') and immediately enumerates the compared fields. It is unmistakably distinct from get_run, list_runs and query_run, and the example makes the two-run shape concrete.

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?

States the decision context explicitly ('Use it to tell whether a revision or a refresh delivered more, less or different data than the run before it') and names both the exclusion and the alternative: 'It does not compare columns or row values; query_run each run for that.'

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