Fabits MCP Server

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

With no annotations provided, the description carries full burden and does well by disclosing key behaviors: it 'Stores authentication token for subsequent requests' (critical side effect), identifies it as part of a two-step login process, and implies it completes authentication. However, it doesn't mention error conditions, token expiration, or security implications, leaving some behavioral aspects uncovered.

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 perfectly concise with three sentences that each earn their place: establishes context ('Step 2 of login'), states core action ('Verify OTP and complete login'), discloses critical behavior ('Stores authentication token'), and provides essential guidance ('Must call fabits_request_otp first'). No wasted words, front-loaded with purpose.

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?

For an authentication tool with no annotations and no output schema, the description does well by covering purpose, prerequisites, and key side effects. However, it lacks information about return values (what happens on success/failure) and doesn't mention potential error conditions or token management details, leaving some gaps for a security-critical operation.

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 100%, so the schema already fully documents all three parameters. The description adds no additional parameter semantics beyond what's in the schema descriptions (e.g., 'user_id' as session identifier, 'phone_number' matching request_otp, 'otp' as one-time password). This meets the baseline 3 when schema does the heavy lifting.

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 specific action ('Verify OTP and complete login') and resource (authentication process), distinguishing it from sibling tools like 'fabits_request_otp' (step 1) and 'fabits_refresh_token' (token renewal). It explicitly identifies this as 'Step 2 of login' with a distinct role in the authentication flow.

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 usage guidance: 'Must call fabits_request_otp first' establishes a prerequisite, and positioning it as 'Step 2 of login' clearly defines when to use it versus alternatives like 'fabits_refresh_token' for token renewal or other non-login tools. This creates clear boundaries within the authentication workflow.

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