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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds real behavior beyond that: numbers compare exactly, arrays match by content by default so an inserted item counts as one addition, and position mode compares index by index. That is meaningful semantics an agent could not infer from the 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?

Three tightly packed sentences with zero filler, front-loaded with the core purpose before the comparison semantics and the mode switch. Every clause carries information.

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 does state the return shape (added/removed/changed values with JSONPath), and annotations cover safety. The remaining gaps are the left/right orientation and no mention of the 200,000-character input limit or how large diffs are returned, but for a 3-parameter diff tool this is close to complete.

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 parameter burden. It fully documents the arrays enum (content vs position, and the default), but says nothing about left/right beyond the implicit 'two JSON documents' — notably which side is the baseline for 'added' vs 'removed' — leaving directionality ambiguous.

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 gives a specific verb and resource ('Compare two JSON documents structurally') plus the exact deliverable ('list every added, removed and changed value with its JSONPath'). That is clearly distinct from siblings like usesignal_format_json or usesignal_encode_decode, so an agent can route without opening any schema.

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 context is only implied: the description explains the default array-matching mode and when to switch to arrays:"position", which is parameter-selection guidance rather than tool-selection guidance. It never states when to reach for this tool over usesignal_format_json or any other sibling, nor any exclusions or prerequisites.

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