Hook Detector

read_retention_graph

Read a YouTube Studio audience retention screenshot (base64 PNG or JPEG) into 100 points and the 21 marks it was read from (1 credit). Not the chart is 422 not_a_retention_chart, free. Same as POST /v1/review/graph.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "read_retention_graph"
  }
}

Input Schema

Name	Required	Description
`image`	No	the screenshot as base64
`api_key`	No
`idempotency_key`	No	1 to 255 visible ASCII characters; the same key and request within 24 hours answer the saved remix and charge nothing; the same key with another request is 422 idempotency_key_reused

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 27, 2026

TDQS

B3.3/5.0

Behavior4/5

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

With no annotations, the description steps up: it discloses the 1-credit cost, that a non-chart image is a free 422, and the specific error code. It omits auth requirements and whether a failed read still consumes credits beyond the stated case.

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

Conciseness3/5

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

Front-loaded and short, but the telegraphic style costs clarity: "Not the chart is 422 not_a_retention_chart, free" is grammatically broken and needs a re-read. Also an output schema exists, yet the description restates the return shape.

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

Completeness3/5

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

Return values are covered by the output schema and the cost/error model is present, but for a credit-charging tool with no annotations the description never says whether an API key is required or what image framing is expected, leaving gaps an agent must guess at.

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 67%, and the description adds real value by constraining the image to base64 PNG or JPEG where the schema only says "base64". However, api_key goes unexplained in both places, so the marginal gain is modest.

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?

Specific verb and resource: reads a YouTube Studio audience retention screenshot and states the output shape (100 points plus the 21 marks). It fails to differentiate itself from nearby review_* siblings, but the resource is distinctive enough that confusion is unlikely.

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

Usage Guidelines2/5

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

No when-to-use or when-not-to-use guidance against alternatives. The closest thing is an error condition ("Not the chart is 422 not_a_retention_chart"), which describes a failure mode, not selection criteria.

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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