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

Annotations already establish readOnly, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description still adds genuinely useful operational context beyond the annotations: the fixed count of 29 entries, zero credit cost, and a deprecation notice naming retired keys ('1xbet', 'afropari') and their replacements, which prevents an agent from passing dead values downstream.

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?

Two sentences, both load-bearing: the first defines the result set and its fields, the second delivers the cost figure and the deprecation caveat. Information is front-loaded and there is no filler or restatement of the title.

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 a zero-parameter, fully annotated, read-only tool with an output schema, this is close to complete — the agent knows what it gets and that it is free to call. The remaining gap is workflow placement: it does not say this list should be consulted before mbc_book_code or mbc_bulk_convert, which a user of those siblings would need.

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?

The tool takes no parameters, so the baseline is 4 and there is nothing for the description to disambiguate. The deprecation note about bare '1xbet'/'afropari' versus '1xng'/'1xglobal' is technically about values consumed by sibling tools, but it is a sensible addition given the zero-parameter schema.

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 names a precise verb and resource — 'List all 29 supported bookmakers' — and enumerates what each entry contains (canonical keys, aliases, code format hints, capability flags). This is clearly a catalog/reference tool, but it never names a sibling such as mbc_book_code or mbc_convert_code to sharpen the boundary, so it stops short of a 5.

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?

Usage context is implied rather than stated: it is evidently the lookup used to discover valid bookmaker keys before conversion, and 'Costs 0 credits' signals there is no penalty for calling it. However, there is no explicit 'use this when / do not use this when' guidance or pointer to an alternative tool.

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