Meridian

Update Plan

plan_update

Edits a Plan Builder plan. plan_id is the uuid or handle from plans_list. Send only what changes: name, description, price_monthly, price_yearly (null removes it), trial_days, features, events. features and events each replace the plan's whole list, so send every entry the plan should keep. Refused when the plan has live subscribers and the change would cost them more (PLAN_LOCKED; make a new version in the Meridian dashboard), and when it would price an active plan while the app cannot charge through Shopify yet (SHOPIFY_BILLING_NOT_READY). An active plan's changes reach new merchants at once. To put a draft live, use plan_activate. Takes the app_id returned by apps_list. Returns the same shape as one plans_list entry.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "app_id": "<app_id>",
      "plan_id": "<plan_id>"
    },
    "name": "plan_update"
  }
}

Input Schema

Name	Required	Description
`name`	No	New plan name, unique among the app's plans.
`app_id`	Yes	The app uuid returned by `apps_list`.
`events`	No	The plan's per-event usage terms. Replaces the plan's whole list. At most one event may have an overage rate above 0, and a plan that charges for usage cannot have a yearly price.
`plan_id`	Yes	Plan uuid or handle from `plans_list`.
`features`	No	The features this plan grants. Replaces the plan's whole list: send every feature the plan should keep. An empty list removes them all.
`trial_days`	No	Free trial length in days (min 0), or null for none.
`description`	No	Description shown with the plan, or null to clear it.
`price_yearly`	No	Yearly price in USD (min 0.01), or null to remove it.
`price_monthly`	No	Monthly price in USD (min 0).
`organization_id`	No	An organisation uuid or slug. When supplied, `app_id` is resolved within that organisation and may be a slug instead of a uuid, mirroring the Meridian web app.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 9, 2026

TDQS

A4.8/5.0

Behavior5/5

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

Goes well past the annotations: it discloses that `features` and `events` replace the entire existing list (and that an empty list removes everything), that `price_yearly` null removes the price, that an active plan's changes reach new merchants immediately, and it names two specific refusal error codes. The only nuance the annotations could mislead on – destructiveHint=false while list replacement can drop entries – is defused because the replacement semantics are stated explicitly.

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

Conciseness4/5

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

Front-loaded with purpose, then update semantics, then failure modes – a sensible order with no filler sentences. Minor waste in 'Takes the `app_id` returned by `apps_list`', which repeats the app_id property description verbatim.

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

Completeness5/5

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

For a 10-parameter mutation with no output schema, it supplies the missing pieces: substitution semantics for the list fields, the lock/billing preconditions, the immediate effect on active plans, and an explicit statement of the return shape ('same shape as one `plans_list` entry'). Nothing an agent needs to call this safely is absent.

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

Parameters4/5

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

Schema coverage is 100%, so baseline is 3; the description earns an extra point by conveying a partial-update contract (send only changed fields) and the null-removal semantics for price_yearly/trial_days/description, which the schema does not state as a general rule. It offers little on the two id-resolution details beyond restating the schema-linked sources.

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

Purpose5/5

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

States a specific verb and resource ('Edits a Plan Builder plan') and immediately routes the adjacent intent elsewhere ('To put a draft live, use plan_activate'), so an agent can separate it from plans_list, plan_create, and plan_activate without opening a schema.

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

Usage Guidelines5/5

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

Gives an explicit partial-update rule ('Send only what changes'), a named alternative for the activation case ('use `plan_activate`'), and the exact conditions under which the call is refused (PLAN_LOCKED with live subscribers, SHOPIFY_BILLING_NOT_READY). The when-to-use and when-it-fails guidance is complete.

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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