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json_merge

Merge a JSON object into existing JSON at a specified dotted path. Use an empty path to merge at the root level.

Instructions

Merge a JSON object at a dotted path (empty path merges at the root).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
dataYes
pathYes
valueYes

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. First observed

TDQS

B3/5.0
Behavior2/5

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

With no annotations, the description carries the full behavioral disclosure burden. It does state dotted-path traversal and empty-path root behavior, but it does not say whether the operation mutates the input, how merge conflicts are resolved, or what is returned. This leaves a significant transparency gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single efficient sentence with no filler. The parenthetical about empty path adds a valuable edge case without bloating the text.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a tool with three required string parameters and no annotations, the description is too sparse. It does not define the data and value parameters, describe merge behavior, or clarify return semantics, so an agent cannot confidently construct a correct invocation without additional assumptions.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate for all three parameters. It adds meaning for path via 'dotted path' and 'empty path', but data and value remain ambiguous — it is unclear whether they should be JSON strings, parsed objects, or something else. This is insufficient for a 3-parameter required tool.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific operation (merge) and resource (JSON object at a dotted path), and the parenthetical clarifies root merging. It is clear enough to distinguish from json_get and json_set, but it does not explicitly reference those siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The empty-path special case gives useful contextual guidance for when to merge at the root. However, there is no explicit comparison to alternatives like json_get, json_set, or write_file, so the decision of when to choose json_merge is only implied.

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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