Extract a value from a JSON string using dot-notation path (e.g., "user.address.city", "items.0.name", "meta.tags"). Supports array index access via numeric path segments.
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | Dot-notation path, e.g. "user.address.city" or "items.0.name" | |
| input | Yes | The JSON to traverse — a JSON string, or the object/array itself. |
| Name | Required | Description | Default |
|---|---|---|---|
| path | No | ||
| type | No | ||
| value | No |
Changes observed during successful MCP inspections.
Input schema / examplesAdded value: +[
+ {
+ "input": {
+ "a": {
+ "b": [
+ {
+ "c": 1
+ },
+ {
+ "c": 2
+ }
+ ]
+ }
+ },
+ "path": "a.b.0.c"
+ }
+]Input schema / properties / input / descriptionPrevious value: -"A valid JSON string to traverse"New value: +"The JSON to traverse — a JSON string, or the object/array itself."Input schema / properties / input / typePrevious value: -"string"New value: +[
+ "string",
+ "object",
+ "array"
+]Output schema / propertiesAdded value: +{
+ "path": {},
+ "type": {},
+ "value": {}
+}Output schema / (root)Previous value: -nullNew value: +{
+ "additionalProperties": true,
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds useful path-syntax context (array index via numeric segments) but omits the most behaviorally relevant fact: behavior on missing paths, type coercion, or how a JSON string input is parsed versus an object input. With annotations carrying the safety burden, this lands at a moderate 3.
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?
Two tight sentences, front-loaded with the core action and followed by the two syntax variants that matter most. Nothing is wasted.
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 simple two-parameter read tool with a full schema and an output schema, the description covers what an agent needs to invoke it correctly. The only real omission is missing-path/edge-case behavior, which keeps it short of a 5.
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 100%, so both parameters are already documented, and the description's path examples duplicate the schema's own example. No additional semantics (escaping, edge cases, root path) are provided beyond the structured fields.
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+resource ('Extract a value from a JSON string') and immediately distinguishes itself from JSON-reshaping siblings like flatten_json or format_json by scoping to path-based traversal. The example paths make the operation unambiguous.
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 is implied by the examples rather than stated. It never says when to prefer this over flatten_json or json_to_csv, nor what happens if the path doesn't resolve (error vs null). Adequate but with a clear gap.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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