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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds real value beyond that by disclosing the auth requirement (router key) and the tenancy scoping (organisation of the key). It says nothing about behaviour on an unknown id or whether a missing/inaccessible mandate errors versus returns empty, leaving a modest gap for a lookup 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?

Two short sentences with the lookup semantics front-loaded and the auth requirement trailing, which is the right priority order. The final sentence partly duplicates the access_key schema note about Bearer headers, so a small amount of text is not earning its place.

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 simple read-only lookup with no output schema and full schema coverage, the description covers the essentials: what is fetched, keyed by what, and under what auth/tenancy. It does not indicate what a mandate record contains or resolve the id/mandate_id duplication, which an agent would still have to guess at.

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. The description restates the id format (man_...) already present in the schema and adds the tenancy implication of the router key, but it does not clarify the documented "Same as id" alias on mandate_id or how that interacts with passing only one of them.

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?

Uses a specific verb+resource ("Read a mandate by id") and gives the id format (man_...) plus the scope (organisation of the router key), which separates it from create_mandate and check_payment_against_mandate. It stops short of naming a sibling explicitly, so it is clear but not maximally differentiated.

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?

"A router key is required" states a prerequisite, which is genuine usage context. However, there is no guidance on when to use this read versus related tools like check_payment_against_mandate or approval_status, so the when-to-use signal is only implied.

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