messente_add_to_blacklistWRITE: add one phone number to the account's blacklist, so Messente will no longer send messages to it. Adding a number already listed is harmless. Messente: POST /phonebook/blacklist.
| Name | Required | Description | Default |
|---|---|---|---|
| phone_number | Yes | Phone number to blacklist, E.164 format, e.g. +37251000000. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is already covered. The description adds the useful nuance that re-adding an existing number is harmless and names the underlying endpoint, but says nothing about auth requirements, rate limits, or error behavior.
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 a 'WRITE:' signal and tightly written, with no filler. The trailing 'Messente: POST /phonebook/blacklist' endpoint reference is low-value for an agent but short enough not to hurt readability.
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 single-parameter write tool with full schema coverage and annotations carrying the safety profile, the description covers what the tool does and its effect adequately. No output schema is needed for a simple blacklist operation, though a note on confirming success would round it out.
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 description coverage is 100% and the phone_number parameter already documents E.164 format with an example and a regex pattern. The description adds only the cardinality note ('one phone number', i.e. not a batch call), which is marginal beyond 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?
The description states a specific verb+resource ('add one phone number to the account's blacklist') plus the downstream effect ('Messente will no longer send messages to it'), which lets an agent distinguish it from messente_check_blacklist and messente_list_blacklist without opening a 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?
The description conveys the purpose and effect of the write, so usage is implied, but it never states when to prefer this over the sibling tools (check_blacklist, list_blacklist) or any prerequisites/preconditions for blacklisting.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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