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

With no annotations, the description carries the full burden and does disclose real behavioral traits: a snapshot of current Companies House state is taken, downstream alerts cover status changes/overdue accounts/new charges/deterioration, and hard quotas exist (5 Free, 50 Pro). It stops short of stating duplicate-handling, auth requirements, or error behavior when the cap is exceeded.

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?

Three short sentences, front-loaded with the core action, then the downstream effect, then the constraint. Every sentence adds information; no filler.

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 no-annotation mutation tool with no output schema, the description covers purpose, side effect (snapshot), downstream use, and quota limits, which is most of what an agent needs. It leaves minor gaps around duplicate adds, quota-exceeded errors, and removal via watch_remove.

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 single parameter has 100% schema description coverage including an example format, so the schema already does the heavy lifting. The description only restates 'by company number' and adds no batching or limit semantics (maxItems=100 is left to the 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?

States a specific verb and resource ('Add UK companies ... to your monitoring watchlist') and constrains the identifier form ('by company number'). It is clearly separable from siblings like watch_remove, watch_list, and get_alerts without opening any schema.

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?

It sketches the monitoring workflow by naming get_alerts as the downstream consumer, so the intent (set up monitoring) is implied. However, it never explicitly says when to prefer this over watch_remove/watch_list, how to obtain valid company numbers (e.g. via search_companies/lookup_company), or what to do when the watchlist quota is full.

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