Developers and agents
UK rules and planning maths, callable
The same engine as the Plenence app: a maintained UK rules dataset with a change feed, and deterministic retirement, inheritance tax, pension relief, salary sacrifice and annual allowance calculations. Every response carries its assumptions, citations and rules version.
Access and pricing
- Without a key: 60 calls a day per IP address.
- With a key (get one): 500 free calls a month, then £0.02 a call, billed monthly. Send
Authorization: Bearer wv_live_…. - Plenence Pro members can connect their own assistant to their own plan through the MCP tools marked “my”, at no extra cost.
REST API
Base URL https://www.plenence.com/api/v1 · OpenAPI 3.1 · API catalog
| Endpoint | What it does |
|---|---|
GET /rules?tax_year=&key= | The validated rules dataset with citations. |
GET /rules/changes?since= | Published rule changes. |
POST /calc/retirement-projection | Retirement projection |
POST /calc/inheritance-tax | Inheritance tax estimate |
POST /calc/pension-tax-relief | Pension tax relief |
POST /calc/salary-sacrifice | Salary sacrifice comparison |
POST /calc/annual-allowance | Pension annual allowance |
curl -X POST https://www.plenence.com/api/v1/calc/inheritance-tax \
-H 'content-type: application/json' \
-d '{"date_of_death":"2027-06-01","home_value":600000,"home_to_direct_descendants":true,"other_assets":250000,"pensions":300000}'Every response: { result, assumptions, citations[{authority,url,rule_key,version,retrieved_at}], rules_version, disclaimer }.
Errors and limits
Errors are JSON, { error: { code, message } }, with a stable code to branch on. Calculations are pure functions of their input, so a retry returns the same answer.
| Status | Code | What to do |
|---|---|---|
| 400 | invalid_input, invalid_json | Fix the fields the message names. Unknown fields are rejected, never ignored. |
| 401 | invalid_key | The key is unknown or revoked; send a valid key or none. |
| 402 | billing_required | Past the free monthly allowance with no API billing: set it up at /account/api. |
| 422 | rule_not_in_force | No validated rule covers that date. |
| 429 | rate_limited | Keyless daily limit reached; wait Retry-After seconds (resets 00:00 UTC) or use a key. |
| 503 | rules_unavailable | Temporary; retry with backoff. |
Every metered response carries X-Free-Calls-Remaining; keyless responses also carry RateLimit-Limit, RateLimit-Remaining and RateLimit-Reset. GET /rules/changes includes the watcher's last run (watcher.last_checked_at), so an empty feed can be told apart from a stalled one.
MCP server
Streamable HTTP at https://www.plenence.com/api/mcp · server card
claude mcp add --transport http plenence https://www.plenence.com/api/mcp
- Public:
get_uk_rule,list_rule_changes,project_retirement,estimate_inheritance_tax,calculate_pension_tax_relief,compare_salary_sacrifice,calculate_annual_allowance. - Your own plan (Pro, with your key):
get_my_financial_picture,get_my_ranked_decisions,run_my_scenario.
Outputs are facts, explanations and analysis. The tools never recommend a product, fund or provider.