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

Annotations already declare readOnly, idempotent, closed-world and non-destructive behavior, so safety is covered. The description adds genuinely new operational context: the x402 payment requirement, the exact price ($0.003 USDC on eip155:8453), and the 20-path ceiling per call — things an agent cannot learn from the structured fields.

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 compact sentences: capability, syntax, cost. The first sentence largely restates the title/schema capability, which is minor waste, but nothing else is padding and the payment detail is placed where it will be seen.

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?

No output schema exists, so the description should hint at return shape; it says "extracts values" but not whether multiple paths yield an object keyed by path or a positional array. Otherwise a 3-parameter, low-complexity read tool is adequately covered, including cost and limits.

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 only 33% (`path` and `paths` are undocumented in the schema), so the description must compensate. It does: it specifies RFC 6901 pointer syntax `/a/b/0`, the dotted-path variant `a.b[0].c`, and `[*]` wildcards, and it ties the 20-item cap to the `paths` parameter. It does not clarify whether `path` and `paths` can be combined, which leaves one real ambiguity.

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 and resource ("extract values from JSON") and immediately names two supported addressing modes. This clearly distinguishes it from siblings such as json_format, json_validate and json_diff, which the description's extraction framing implicitly rules out.

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?

"Reads one value by RFC 6901 JSON Pointer ... or a dotted path" plus "Up to 20 paths per call" implies the single-path vs. batch-path usage, but never explicitly says when to use `path` versus `paths`, nor does it name an alternative tool. Usage is inferable rather than stated.

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