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Add an expense group member

well_create_expense_group_member
Idempotent

Add one person of this workspace as a member of a shared-expense group. Only a member can pay a line, hold a share or take part in a repayment. It writes only inside Well and sends nothing.

person_id is a person record of this workspace, such as one well_create_person returned. A person already in the group is refused with already_a_member, and nothing changes.

Call it only after the person said yes to adding this member, in this conversation.

Read outcome: written with member, or refused means nothing was written. reason names why: group_not_found (no such group in this workspace), person_not_found (a person id names no person of this workspace), not_a_member, payer_not_a_member, from_not_a_member or to_not_a_member (that person is not a member of the group: add them first), currency_mismatch (the group holds one other currency), invalid_amount, invalid_weight, no_shares, duplicate_share, same_person, already_a_member, caller_not_a_member or caller_not_a_person_here (the call names no person of this workspace).

When the token authorizes one workspace, call this directly — no workspace call is needed first. When it authorizes several, this read will not guess which one you mean: pass workspace_id on the call.

Input Schema

NameRequiredDescriptionDefault
person_idYesA person record of this workspace.
workspace_idNoTarget workspace. Omit when the token authorizes one workspace. Required when it authorizes several — a write lands in exactly one workspace and this call would not say which.
conversation_idNoThe conversation id returned by the previous Well result, in its meta under well/conversation_id, in its structuredContent, or in its JSON text block. Pass it back on every call in the same conversation, including a call a card makes, so the chosen workspace and the earlier answers still apply. It decides the conversation on its own: nothing the host states about the session replaces it. Omit it only on the first call of a conversation.
idempotency_keyNoOptional client-supplied key. A retried write with the same key returns the original result instead of re-applying the operation.
workspace_scopeNoRestrict this call to the family: the token's primary workspace plus the company workspaces under it that you are a member of. Unrelated authorized workspaces drop out of the read; row reads merge across the family, while a per-workspace figure still reports exactly one workspace.
expense_group_idYesThe group, a row of `well_list_expense_groups`.

Output Schema

NameRequiredDescriptionDefault
errorNo
memberNo
reasonNo
outcomeNo
successYes
conversation_idNoThe conversation this result belongs to. Pass it back as the conversation_id argument on every later Well call in the same conversation.
newly_connectedNoTools that connected to this workspace since the last result and that no session was told about yet, oldest first. Present only when at least one tool is new. The connected-line rule says when to tell an entry; when it does, one line per entry, in the person's language: "<name> is connected.". Never fold several entries into one sentence. Each entry comes back once, on one result only: never repeat its line later.
expense_group_idNo
conversation_id_noteNoPresent only when the server opened a fresh lane, stating that no choice recorded earlier was read.
conversation_id_sourceNoWhere the conversation id came from: the host's own request meta, the caller's argument, or a fresh lane the server opened.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4/5.0
Behavior4/5

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

With readOnlyHint=false, idempotentHint=true and destructiveHint=false already declared, the description still adds meaningful behavior: writes 'only inside Well and sends nothing', a repeat member is refused with already_a_member and nothing changes, and outcome/refused semantics. It loses a point for loose/incorrect wording ('this read will not guess' for a write tool) and for refusal codes (currency_mismatch, invalid_amount, no_shares, duplicate_share, same_person) that belong to expense-line creation rather than membership, which can mislead an agent diagnosing failures.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Purpose is front-loaded and the operational guidance is well organized, but the enumeration of refusal reasons is bloated and includes codes irrelevant to this operation, forcing the agent to filter noise. Several sentences recapitulate schema descriptions (workspace_id, conversation_id) rather than adding information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given an output schema exists, the description need not explain return shape, yet it usefully explains outcome/reason values, the workspace-routing rule, idempotency and a consent precondition — enough for an agent to invoke correctly. The irrelevant refusal codes are the one completeness blemish: they suggest error paths this call cannot produce.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all six parameters are already documented in the schema, including the workspace_id conditional. The description mostly restates that (workspace_id one-vs-many rule) and adds only a marginal link to well_create_person as a source of person_id; baseline 3 applies when the schema carries the semantics.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Add one person ... as a member of a shared-expense group') and immediately clarifies what membership enables (pay a line, hold a share, take part in a repayment). That scope cleanly separates it from siblings such as well_create_expense_group, well_create_expense_line and well_create_expense_settlement.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a real precondition ('Call it only after the person said yes ... in this conversation') and explicit workspace-routing guidance (call directly when the token authorizes one workspace, pass workspace_id when it authorizes several). It stops short of naming an alternative tool when this one is wrong (e.g. well_list_member_candidates to find a person), so it is clear context without explicit exclusions.

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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