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lago

by io.usefulapi
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Create usage event

lago_create_event
Destructive

Records a usage/metering event in Lago. This WILL be counted toward the customer's usage and affects billing. Idempotent via transaction_id. Lago API: POST /events with body { "event": { ... } }.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
codeYesThe billable metric code this event targets (required).
timestampNoUnix timestamp in seconds (or ISO); defaults to event reception time.
propertiesNoAdditional event properties used to compute the fee (required for sum/max/unique aggregations).
transaction_idYesUnique identifier for the event — the idempotency key (required).
external_subscription_idYesThe subscription external id to link the event to (required).
precise_total_amount_centsNoPrecise total amount in cents, used by the dynamic pricing model.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4/5.0
Behavior4/5

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

Annotations already mark destructiveHint=true; description adds that events are counted toward usage, affect billing, and are idempotent, plus API details. No contradiction.

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?

Two sentences with no waste; key info front-loaded.

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

Completeness4/5

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

Given no output schema and moderate complexity, description covers primary behavior. Missing return value/error info but sufficient for a creation tool.

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

Parameters3/5

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

Schema coverage is 100%, so baseline is 3. Description adds idempotency context for transaction_id but no further parameter elaboration. Adequate.

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?

The description clearly states the tool records a usage/metering event that affects billing, with idempotency via transaction_id and API endpoint. It distinguishes from sibling analytics/read tools.

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 description implies usage for metering events but does not explicitly guide when to use vs alternatives like lago_create_customer or other creation tools.

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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