Central Bank of Brazil series: SGS, Focus and PTAX without the traps

Three API limits measured live, level series vs. rate series, and what the ODbL requires

Published 31 August 2026. Every behaviour and value described here was measured live against the Central Bank APIs on the publication date; nothing is inferred from documentation.

The Central Bank of Brazil publishes three different things, by three different routes, and beginners tend to treat them as one:

• the SGS (time series management system) — thousands of numbered series: the policy rate, inflation, exchange rates, credit, monetary aggregates;
• Focus — the weekly market-expectations survey, which is not a time series but a matrix of indicator × horizon × statistic;
• PTAX — the official closing exchange rates, served by a separate API.

The SGS: everything is a series number

You do not query “inflation”. You query series 433. Not “the dollar”; series 1. The policy rate target is 432. Finding the code is half the work.

Real response on 2026-08-31 — monthly IPCA inflation:

[{"data":"01/05/2026","valor":"0.58"},
 {"data":"01/06/2026","valor":"0.16"},
 {"data":"01/07/2026","valor":"0.07"}]

Three API limits, measured

1. A window longer than 10 years on a daily series is refused with HTTP 406.

.../bcdata.sgs.1/dados?formato=json&dataInicial=01/01/2011&dataFinal=31/12/2025
→ HTTP 406

A 3-year window on the same series returns 755 observations.

2. An open window is refused too, for the same reason: with no end date the API assumes today, and series 1 begins in 1984.

3. ultimos/N is capped at 20, in every periodicity — and above it the request fails with HTTP 400 rather than returning 20.

Put the three together and a 15-year daily series has to be sliced, fetched and merged without duplicating the seams. In practice slice at 3 years, not the permitted 10: a decade-long daily window costs 10–20 seconds upstream and can be cut off around 30.

The trap that raises no error: variation on a series that already is variation

Monthly IPCA already is a percentage change. Summing twelve monthly values to get the annual figure is wrong, because inflation compounds:

compounded = [ Π (1 + vᵢ/100) − 1 ] × 100

With the three real months above, the sum gives 0.8100 and compounding gives 0.8114 — the sum understates. Small over three months; not small over twelve, or in any period with high inflation.

The rule: before computing a variation, ask whether the series is a level or a rate. Levels (the exchange rate, credit stock, GDP) admit endpoint-to-endpoint change. Series that already are period-on-period rates require compounding. The same applies to resampling: turning monthly inflation into annual is geometric composition, not an average.

Focus: the policy rate’s axis is not a horizon

For most indicators the expectation has a horizon — monthly, quarterly, annual, or inflation accumulated over 12 and 24 months. Each response carries mean, median, standard deviation, minimum, maximum and the number of respondents, plus a Top 5 variant for the best recent forecasters.

The policy rate is different: its axis is the monetary policy committee meeting (in the form R1/2026), not a time horizon. Treating it as one more horizon is the most common conceptual error here.

Another asymmetry: the set of indicators changes with the scope — 9 in the monthly scope, 26 in the annual. There is no single “list of Focus indicators”; there is the list of that scope.

PTAX: not every quote is compiled by the Central Bank

The Central Bank compiles the US dollar PTAX. Cross-currency parities are not: they come from an information agency (Refinitiv) and are redistributed by the Central Bank. The difference is legal and methodological, not cosmetic — and the Bank’s own liability disclaimer must be passed through verbatim.

The licence asks for things

Central Bank data is released under the Open Data Commons Open Database License (ODbL) v1.0. That is not CC0, not CC BY and not public domain. The ODbL carries three obligations that survive redistribution: attribution, share-alike on derived databases, and an anti-DRM clause.

Checked against the source on 2026-08-13: 4,259 of the 4,260 datasets in the Bank’s open-data portal declare license_id: "odc-odbl".

Where an AI assistant fits

Asking a model “what is the policy rate today?” returns a number from training: possibly right, possibly three committee meetings out of date, with no source. Plugging in the SGS buys provenance — the series, the period, the canonical URL, the real extraction instant and the licence — and moves the traps above to the server side.

That is what bcb-br-mcp does: 15 tools over SGS, Focus and PTAX, with a curated catalogue of 135 series verified against the source, for clients that speak MCP.

With or without a tool, the two questions that avoid most errors are the same: is this series a level or a rate? and who compiled this number?

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Server: bcb-br-mcp · hosted endpoint at https://bcb.sidneybissoli.com/mcp · code under MIT. Central Bank data under ODbL v1.0 — https://opendatacommons.org/licenses/odbl/1-0/.