Corr (Correspondence Chess) – Definition & Overview

Corr

Definition

Corr is shorthand for “correspondence chess,” often written as “CC.” It refers to chess played at long time controls (typically days per move) where players can consult resources between moves. In modern practice, Corr usually means server-based correspondence chess (e.g., ICCF events), but historically it included postal, telegraph, and email chess.

In Corr events governed by the International Correspondence Chess Federation (ICCF), the use of analysis tools such as Engines and Endgame tablebases is allowed. In contrast, many casual or platform-based “daily” games explicitly ban engine help; always check the event’s rules.

How “Corr” is used in chess

• As a label: Players and databases tag games as “corr,” “CC,” or “ICCF,” distinguishing them from OTB (over-the-board) games.
• In discussion: “This was found in corr,” or “a corr novelty,” meaning the idea arose or was tested in correspondence play.
• In PGN headers: Events may be marked with ICCF tournament names; time controls appear as days-per-move (e.g., “10 moves/30 days” or increments like “3 days/move”).
• As a study source: Because moves are deeply researched, corr games are prized for reliable Opening Theory and high-quality Endgame technique.

Time controls and rules (what to expect)

• Days per move: Typical controls are 3 days/move, 5 days/move, or 10 moves in 30 days, often with a “vacation” allowance.
• Draw claims: Standard rules apply—Threefold, Fifty-move, and customary draw offers (unless the event uses “no draw offers”).
• Assistance policy:
  • ICCF: Human+engine analysis is permitted; Tablebase use is standard in relevant endgames.
  • Other platforms/leagues: Some forbid any engine or outside assistance. Violating assistance rules is Cheating—verify event regulations.
• Adjudication: In postal-era corr, unclear endings could be adjudicated by experts. Today, server-based results are typically played to conclusion.

Strategic significance and practical approach

Corr emphasizes accuracy, preparation, and project-style analysis. Because you can think for hours or days per move, mistakes are rare at the top level, and many games demonstrate near-perfect technique.

• Opening preparation:
  • Deep dives into main lines and Prepared variations; hunting for reliable Novelty/TN ideas.
  • “Colors reversed” ideas and offbeat systems can be effective if they yield lasting Practical chances.
• Middlegame planning:
  • Long forcing calculations, extensive candidate-move trees, and positional squeezes with sustained Prophylaxis.
  • Meticulous exploitation of structural themes: Hanging pawns, Isolated pawn, Minority attack, Outpost.
• Endgame mastery:
  • Frequent transitions to theoretically critical endings: Opposition, Lucena position, and Fortress motifs.
  • Tablebase-perfect play shapes both technique and opening choices (aiming for winning tablebase outcomes or known Theoretical draws).
• Time management:
  • Use your “clock bank” strategically; maintain consistent analysis logs and version control for lines you’re exploring.
  • Plan during the opponent’s time; draft multiple replies to preserve flexibility.

Historical notes and modern trends

• Postal era: Moves traveled on postcards with algebraic or descriptive notation. Famous postal events date back to the 19th century.
• World champions: Cecil Purdy won the first ICCF World Correspondence Championship (1950–53). Later luminaries include Hans Berliner (1965–68), Tõnu Õim, and Grigory Sanakoev.
• The engine era: ICCF’s allowance of engines transformed Corr into “centaur”-style chess. Top corr games often feature near-errorless play and cutting-edge opening ideas.
• Impact on OTB: Many robust novelties debut in corr before appearing in elite tournaments; corr analysis frequently refines evaluations of sharp openings (e.g., Najdorf, Grünfeld, and King’s Indian structures).

Example 1: A “corr-style” main line you might prepare

This Slav Defense line is a typical starting point for corr preparation—solid, deeply analyzed, with many sub-branches where a small novelty can matter. A corr player would examine dozens of candidate move-orders from move 10 onward, checking transpositions and endgame trends.

Line: 1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 dxc4 5. a4 Bf5 6. e3 e6 7. Bxc4 Bb4 8. O-O Nbd7 9. Qe2 O-O 10. Rd1

Corr focus from here:

• Testing move-orders like 10...Qe7, 10...Bg4, or 10...Qa5 to steer into favorable pawn structures or minor-piece endings.
• Preparing a safe endgame with a durable Space advantage or aiming for a specific Pawn break (e.g., ...c5 or e4-e5).

Example 2: Corr-level endgame awareness

Endgames are decisive in corr. Positions like the Lucena or Philidor setups are memorized and verified with Syzygy tablebases. A typical Lucena-style position (rook and pawn versus rook) requires Building a bridge to shield the king from checks; corr specialists will know the exact winning technique and the traps that lead to a Dead draw.

Famous correspondence highlight

Hans Berliner vs. Yakov Estrin, World Correspondence Championship Final, 1965–68, is a landmark game in the Two Knights Defense—celebrated for deep home analysis and its lasting theoretical impact. It remains a touchstone for how corr research can reshape opening evaluations.

Notation, databases, and record-keeping

• Game logs: Maintain structured trees of “main line,” “Drawing line,” and “speculative branch” analysis with clear timestamps and sources.
• PGN discipline: Store candidate lines and evaluations; tag positions with strategic labels (e.g., “play for Opposite bishops grind,” “Pawn majority endgame favorable,” “Fortress risk”).
• Database hygiene: Separate OTB results from corr results when searching for novelties; corr databases often contain stronger defensive resources.

Tips and best practices for Corr

• Pick openings that fit a long-form workflow—balanced risk, clear plans, and endgames you like.
• Cross-check every forcing line: engine lines, human sanity checks, and motif-based verification (pins, Deflection, Interference, Zugzwang ideas).
• Target small, stable advantages over flashy tactics unless you’ve confirmed the entire sequence.
• Respect event rules about assistance; when engines are prohibited, rely on your calculation and trusted literature only.
• Time discipline: Avoid time scrambles; set a review cadence (e.g., morning/evening) and log decisions.

Interesting facts and anecdotes

• Postal codes: In the postcard era, players often used compact move-coding systems to save space and avoid misreads.
• Draw rates: At the elite ICCF level, draw rates can be very high—yet decisive games often hinge on a single, deeply prepared Quiet move or an endgame nuance spotted weeks in advance.
• From corr to OTB: Entire opening reputations have shifted after corr players unveiled reliable improvements that OTB grandmasters later adopted.

Related terms

See also: Correspondence, Daily chess, Engine, Prepared variation, Opening theory, Endgame tablebase, Theoretical draw, Building a bridge.

Summary

Corr (correspondence chess) is the long-form, research-driven side of the game, where precision preparation, engine-aware verification (when permitted), and endgame literacy reign. Whether you’re mining a main line for a durable novelty or steering into a tablebase-favorable ending, Corr rewards patience, structure, and depth of understanding.