How we source and review numbering guidance

Editorial principles

Source hierarchy

Current national regulator or numbering administrator first; ITU-T recommendations and administration-submitted national numbering plans second; provider documentation only for that provider’s own result semantics.

Safe examples

Use officially reserved or fictional ranges where confirmed. Otherwise use X placeholders and label the value as a pattern, never as a callable E.164 number.

Review dates

Time-sensitive country guidance carries a last-verified date. A page without reviewed example data remains a lookup page and does not fabricate a walkthrough.

Conflict resolution

Prefer the newer primary source with direct responsibility for the national plan. Record the conflict, effective date, and transition period instead of silently merging incompatible rules.

Machine-readable parity

Country HTML, API, OpenAPI, MCP, and LLM documentation use the same enriched accessor. Optional example payloads include their source and verification metadata.

Corrections

Reported errors are checked against primary sources, covered by a regression test where possible, and corrected across every affected delivery surface.

Update and review cadence

We review source notifications and high-use country pages when a regulator or the ITU publishes a numbering change. The guide index, sitemap, API documentation, and LLM discovery files are updated in the same release as new reviewed content. Automated tests enforce country-code consistency, leading-zero behavior, safe examples, primary-source metadata, and parity between the two llms.txt build sources.

A verification date means the cited source was checked on that date. It is not a promise that a national administration will not announce a later change. For a production routing or compliance decision, re-check the linked primary source and the relevant service provider.

Core standards

• ITU-T E.164: The international public telecommunication numbering plan

  International Telecommunication Union; verified 2026-07-19.

• ITU-T E.123: Notation for national and international telephone numbers

  International Telecommunication Union; verified 2026-07-19.