YNAB MCP Server

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It correctly identifies this as a mutation operation ('Update'), describes the return format, and mentions default behaviors (month defaults to current month, budget_id uses default if omitted). However, it doesn't disclose important behavioral traits like whether this requires specific permissions, if changes are reversible, rate limits, or error conditions—significant gaps for a mutation tool.

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 well-structured with purpose statement, usage guidance, parameter explanations, and return description—all in appropriate sections. It's front-loaded with the core purpose. While efficient, the 'Args:' and 'Returns:' sections could be slightly more concise, but overall there's minimal waste.

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 this is a mutation tool with no annotations but with an output schema (which handles return values), the description provides good coverage. It explains the tool's purpose, usage, all parameters, and mentions what's returned. The main gap is lack of behavioral context around permissions, side effects, or error handling, which would be valuable for a budget update 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?

With 0% schema description coverage, the description fully compensates by providing clear semantic explanations for all 4 parameters. It explains what each parameter represents (category UUID, budgeted amount in milliunits with example, month format with default, budget ID behavior), adding substantial value beyond the bare schema. The parameter documentation is comprehensive and helpful.

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 ('Update the budgeted amount'), target resource ('for a category in a specific month'), and distinguishes it from sibling tools like 'update_category' (which likely updates category metadata rather than monthly budget allocations). The verb+resource combination is precise and unambiguous.

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 clear context for when to use this tool ('Use this to move money between categories or adjust budget allocations'), which gives practical guidance. However, it doesn't explicitly state when NOT to use it or mention specific alternatives among the sibling tools (like whether 'update_category' serves a different purpose).

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