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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It effectively discloses key traits: activation is instant without browser or human action, returns a session_token, and includes 100 free tokens on signup. These behavioral details go beyond what the schema provides. The only missing information is potential cost implications after the free tokens, but the free token offering is clearly stated, making this mostly transparent.

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?

The description is extremely concise with six short lines of prose plus a parameter list. It front-loads the key behavioral claims ('Activate instantly. No browser, no human action needed.') and provides actionable instructions immediately. Every sentence adds value—no wasted words. The parameter list is cleanly formatted with single-line explanations.

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?

Given the tool has 4 parameters, no output schema, and no annotations, the description covers the essentials: what the tool does, what it returns, where to get pre-requisite data (list_channels), and what to do with the output. The only minor gap is lack of error handling or failure modes, but the tool appears simple and low-risk. It is sufficiently complete for an agent to invoke correctly.

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 0%, so the description must compensate. It defines all four parameters clearly: human_email, channels, agent_email, and source with an example for channels and default guidance for source. The descriptions add meaning beyond the schema's empty titles by providing context like 'Your agent's email address' and 'How you found us (e.g. 'mcpregistry')'. The only gap is that required status is implicit from the list, but the schema already marks required 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?

The description clearly states the tool activates a subscription ('Activate instantly') and specifies the resource it operates on. It distinguishes itself from siblings by mentioning 'Returns a session_token — store it for daily get_bundle calls', which differentiates it from get_bundle and list_channels. The verb 'start_subscription' combined with the description of instant activation provides a specific and unambiguous purpose.

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?

The description provides explicit guidance on when to use this tool and what to do afterward: 'store it for daily get_bundle calls' tells the agent to use the session_token with get_bundle subsequently. It also informs the agent about available channels via 'Call list_channels for available slugs', directing to a sibling tool for prerequisites. This covers both when to use and what actions to take before and after.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.