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

Beyond the annotations (readOnly/openWorld/non-destructive), the description discloses rate limits (60/hour, 300/day per IP and session), that no API key or signup is needed, that keys raise limits with anonymous fallback after quota, that source licence warnings apply, and that results carry provenance with SI normalisation. This is substantial operational context the structured fields do not carry.

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?

Front-loaded with purpose and the calling rule, then operational details; most sentences earn their place. The brand line ("TerraMCP is a Wrench AI service") is filler that dilutes an otherwise tight paragraph.

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?

With no output schema, the description does cover the return shape at a high level (source data, provenance, SI normalisation) plus licensing and rate limits. It could be slightly more specific about what a result record contains, but it is adequate for a 5-parameter read-only search tool with full schema coverage.

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 coverage is 100%, so the baseline is 3, but the description adds a real constraint the schema does not encode: although no parameter is marked required, the agent must supply either a name or both coordinates. It restates the 50 km radius cap, which is already in the schema, so it does not rise to a 5.

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 (Find), resource (SEPA monitoring stations), geography (Scotland), and the two lookup modes (name or WGS84 lat/lon). This cleanly separates it from siblings like sepa_series and sepa_values, which deal in readings rather than station discovery.

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?

"Supply a name or both coordinates; radius maximum 50 km" is an explicit calling rule that tells the agent the two valid invocation shapes. It does not, however, tell the agent when to prefer this over other station tools such as rainfall_stations or ea_groundwater_stations, so tool-selection guidance is absent.

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